2010-2011 Seminars and Previous Seminars (Past months or Previous years)

Note that if the talk's pdf or ppt is available after the talk, you can get it by clicking on the talk title.

Physics/Astronomy C290C Cosmology Seminar
The Physics/Astronomy C290C series consists of the LBNL-Physics-Astronomy Cosmology seminars held Tuesdays 1:10-2:00 pm in room B5 Hearst Field Annex (also videoconferenced to LBL 50A-5131). Feel free bring your lunch.
Please contact Joanne Cohn to add to this list or to suggest speakers.

Speaker/Visitor Info is here.

Note that there are also other talks which generally might be of interest, including Cosmology Workshops and:

May 2011:
May 3 , Tuesday 1:10 pm
Mark Vogelsberger, Harvard-CfA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"New trends in computational cosmology"
Numerical simulations play now a fundamental role for the understanding of structure formation. Especially, on large scales these simulations turned out to be very successful when compared to observations. I will focus in my talk on two new methods in the field of computational cosmology: the study of dark matter on the scales relevant for direct detection experiments and a new scheme to model the hydrodynamic equations. Both methods allow significantly better numerical resolution for the study of dark matter and baryons. I will briefly introduce these new schemes and discuss their application to cosmological simulations with important consequences for dark matter detection and the modeling of galaxy formation.
May 6 , Friday 12:00 pm (INPA Journal Club)
Jake VanderPlas, Washington
LBL 50-5026 (INPA Room)
"Gappy Weak Lensing: KL Interpolation of Shear Fields"
Surveys of gravitational shear due to large-scale structure are becoming an important tool for precise measurements of cosmological parameters, including the possible evolution of dark energy. Many of the new statistical tools being developed in this field rely on obtaining unbiased lensing mass maps over large fields: fields which will, in general, have complicated geometries and masking due to inhomogeneous sky coverage, foreground sources, etc. We have developed an interpolation procedure for gappy shear fields based on Karhunen-Loeve (KL) decomposition. Along with interpolation, the KL analysis results in a suppression of noise on scales relevant to cosmological studies using shear peaks. In this talk, I will review recent studies of the cosmological information encoded in high-convergence regions of shear fields, and show how our new KL framework addresses some potential problems with this approach.
May 10, Tuesday 1:10 pm
Masahiro Takada, IPMU
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Subaru weak lensing study of X-ray luminous clusterss"
We have used Subaru data to conduct a detailed weak-lensing study of the dark matter distribution in a sample of 50 X-ray luminous galaxy clusters in the redshift range 0.15 < z <0.3. We have in detail explored the best-available accuracy of estimating cluster masses from weak lensing information, for each cluster basis and for stacked cluster signals and also using several methods (the model profile fitting and the model-independent aperture mass estimate). We have also developed the new 2D shear fitting method where the two-dimensional weak lensing signals are fully used. Some highlights of our findings are (1) cluster mass enclosed by the spherical over-density 500 can be constrained at 10-20% accuracy for individual clusters and (2) the mass-halo concentration scaling relation is found at a 6-sigma level, and (3) a significant detection of the elliptical shape of dark matter halos at 7-sigma level. If time allows, I will also talk about prospects of future surveys such as Subaru Hyper SuprimeCam survey for conducting cluster-based cosmology aimed at exploring the nature of dark energy as well as testing gravity theory on cosmological scales.
May 13, Friday 12:00 pm (INPA Journal Club)
Daryl Haggard, Northwestern
LBL 50-5026
"The Impace of Galaxy Environment on the X-ray AGN Fraction"
Galaxy formation models must reproduce the AGN fraction as a function of host color and environment. To date, AGN surveys based on optical spectroscopic classification are inconclusive, e.g. some find no environmental dependence while others find a trend similar to starformation rate when selecting by luminosity, and optical emission line classification can falter for AGN at z > 0.4. X-ray selection, with no such limitation, yields greater completeness for AGN than even deep optical spectroscopy, and is much less biased against intrinsic absorption. Here we use a unique sample from the SDSS and the Chandra Multiwavelength Project (ChaMP) to determine the X-ray AGN fraction (log Lx > 42) as a function of local galaxy environment (Bayesian 10th nearest neighbor density). For each X-ray-detected galaxy in the Haggard et al. (2010) ChaMP/SDSS sample we define a control sample of SDSS galaxies with statistically equivalent stellar mass and redshift in order to quantify the relative over- or under-density of AGN environments and to quantify the relationships between star formation, accretion, and environment. Our sample includes ~1600 X-ray detections and over 10^5 SDSS galaxies with Chandra X-ray luminosity limits and thus represents the widest (~20 sq.deg), most uniform study of AGN activity as a function of galaxy environment to-date.
May 17 , Tuesday 12:10 pm--please note special time
Tsz Yan Lam, IPMU
544 Campbell Hall (also videoconferenced to LBL 50A-5131 if possible)
"Velocity Probe in Cosmology"
In this talk I will describe some of my recent work on using large-scale velocity probes to constrain cosmology. I will explain how models with primordial non-Gaussianity leave signatures on the velocity PDF of both dark matter field and biased tracers. I will then present an analytical model to describe the velocity profile around massive clusters and its potential to probe modified gravity.
May 17, Tuesday 4:00 pm (RPM)
Pat McDonald, LBNL
LBL 50A-5132
"The Latest on the Lyman-alpha Forest"
I will discuss recent BOSS results on measuring large-scale correlation in the Lyman-alpha forest absorption. I will also discuss the expected future measurements, from BOSS and hopefully BigBOSS. I will also discuss the theory needed to understand these measurements.
May 20, Friday 12:00 pm (INPA Journal Club)
Reiko Nakajima, Berkeley/LBL
LBL 50-5026 (INPA Room)
"Photometric redshift requirements for lens galaxies in galaxy-galaxy lensing analysis"
Weak gravitational lensing is a valuable probe of galaxy formation and cosmology. However, quantifying its signal to mass requires redshift information of lens and source. In this talk, I will discuss the use of photometric redshifts (photo-z) in weak gravitational lensing, in particular for applications with galaxy-galaxy lensing. We have used the ZEBRA template-based method to estimate the redshifts from SDSS DR8 photometry, for both lens and source catalogs. A heterogeneous set of spectroscopic surveys (zCOSMOS, EGS, VVDS, PRIMUS+DEEP2) were used to calibrate the photo-zs, which were modified to accurately represent the SDSS photometric sample. We find the photo-z errors to be large (sigma_{\Delta z / (1+z)} ~ 0.1, averaged over all sample). The photo-z errors affect the estimates of lens galaxy absolute luminosity and stellar mass, which determine the galaxy-galaxy lensing stacking bin width. While the photo-z bias in the lensing signal can be large, its uncertainty can be small---after correcting for the bias, the uncertainty in the lensing signal can be as small as 3 per cent, for the case when lens redshifts are known.
May 26, Thursday 4:00 pm (RPM)
Eric Gawiser, Rutgers
LBL 50A-5132
"Probing Dark Energy and Dark Matter using Distant galaxies from HETDEX and LSST"
The spatial clustering of distant galaxies is a powerful probe of both the nature of those galaxies and of fundamental physics. The MUSYC collaboration used the connection between galaxies and their dark matter halos to identify distant Lyman Alpha Emitting galaxies as the progenitors of typical present-day galaxies like the Milky Way. The HETDEX experiment will discover nearly one million of these Lyman Alpha Emitting galaxies during the next three years and will use them to determine the expansion history of the universe revealed by Baryon Acoustic Oscillations. These measurements will determine the dark energy equation-of-state and will measure the curvature of the Universe to 0.1% precision. The forthcoming Large Synoptic Survey Telescope (LSST) will greatly expand upon these results, using billions of distant galaxies to measure the evolution of the dark energy equation of state, to seek evidence for modifications to General Relativity, and to constrain the masses of cosmological neutrinos. I will provide an overview of the cosmological structure formation theory and experimental techniques that enable these measurements.
May 27, Friday 12:00 pm (INPA Journal Club)
Nic Ross, LBL
LBL 50-5026 (INPA Room)
"BOSS and The Height of the Quasar Empire"
The SDSS-3 Baryon Oscillation Spectroscopic Survey (BOSS) is assembling an unprecedented dataset of high, z>2, quasars. With nearly two years of observations already complete, 50,000 z>2.2 objects have been spectroscopically identified, a third of the final sample. In this talk, I plan to: (i) Introduce and gave the latest news on the BOSS Quasar Survey; (ii) describe the techniques that went into the target selection necessary to detect these objects; (iii) report on some of the initial science results from the BOSS project, including the quasar luminosity function and the variable nature of luminous AGN; and (iv) give some very early results on new investigations into the MIR (WISE) and FIR (Herschel) properties of BOSS quasars, and how these could tie-in to the next generation of large (ground-based) spectroscopic surveys.

June 2011:
June 10, Friday 12:00 pm (INPA Journal Club)
Josh Meyers, LBL
LBL 50-5026 (INPA Room)
Type Ia supernovae and their host galaxies.
Several recent studies have reported unexpected correlations between the properties of Type Ia supernovae and their host galaxies. For example, the slope of the empirical brightness-color relation used to standardize SNe Ia appears to be smaller for SNe hosted by passive galaxies than for those hosted by star-forming galaxies. More massive galaxies and those with less star formation also appear to host brighter SNe Ia, after standard light curve shape and color corrections are applied. In this talk, I will discuss how the correlated properties of SNe Ia and their hosts offer opportunities to improve the efficiency and accuracy of SN surveys, particularly at high redshift. At the end of the talk, I will describe an ongoing program to use high signal-to-noise ratio Keck spectroscopy of nearby SN Ia hosts to pinpoint the underlying physics of host-galaxy -- SN correlations.

July 2011:
July 1, Friday 12:00 pm (INPA Journal Club)
Eric Huff, Berkeley
LBL 50-5026 (INPA Room)
Seeing in the Dark: Cosmic Shear in SDSS
I discuss preliminary results from a first cosmic shear measurement in SDSS. We have coadded 250 square degrees of multi-epoch SDSS imaging along the celestial equator, optimizing for weak lensing measurement. We employ standard techniques for shape measurement, shear calibration, and inference of the redshift distribution, and perform a wide array of tests that show that the systematic errors for this measurement are probably negligible compared to the statistical errors. We analyze the shear autocorrelation with and without WMAP7 priors, and produce competitive constraints on the matter density and the amplitude of the matter power spectrum at redshift z=0.6.
I will also discuss some new results on lensing magnification. Motivated by the need for greater signal-to-noise in weak lensing measurements, we have used tight photometric galaxy scaling relations to measure a galaxy-galaxy magnification signal with many times the signal-to-noise of previous magnification results. I describe how minor improvements on this work may permit magnification measurements with signal comparable or possibly even superior to shear.

Past Months

(Previous years)
April 2011:
Apr. 1, Friday 12:00 pm (INPA Journal Club)
Ashley Ross, Portsmouth
LBL 50-5026
"Measuring and Analysing Galaxy Clustering with Photometric Surveys"
Wide-field, multi-band photometric surveys provide a wealth of data. The Sloan Digital Sky Survey (SDSS) has produced photometric redshift catalogs containing over 20 million galaxies, The Dark Energy Survey (DES) expects to obtain photometric redshifts for over 200 million galaxies, and The Large Synoptic Survey Telescope (LSST) expects over 1 billion photometric redshifts. This extreme amount of data provides great opportunities for both the study of galaxies and of cosmology. I will introduce the measurement and analysis techniques required to measure and interpret galaxy clustering. I will present measurements I have made using data from the SDSS photometric redshift catalog, split by galaxy type and redshift. I will describe how these measurements yield insight into the halo-occupation-distributions of red and blue galaxies, galaxy evolution/formation, and the bias/luminosity relationship of red galaxies. I will finish with a discussion of the prospects of future surveys, such as DES, including projections for the detection and measurement of redshift-space-distortions.
Apr. 5, Tuesday 1:10 pm
Olivier Dore , JPL
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Planck Early Measurements of the Cosmic Infrared Background Anisotropies"
Since it reached the Lagrange point L2 in august 2009, Planck has been observing the sky at frequencies ranging from 30 to 857 GHz, measuring not only the cosmic microwave background, but also everything else in the universe that radiates at these frequencies. The first scientific results from Planck cover a wide range of galactic and extragalactic astrophysics, including clusters, extragalactic radio sources, Cosmic Infrared Background (CIB), and spinning and thermal dust in the Milky Way.
In this talk, after briefly introducing the Planck instrument, I will focus on Planck early measurements of the CIB. The CIB is the far-infrared relic emission from galaxies formed throughout cosmic history. It appears as a a cosmological, diffuse, background light. Being produced by the star heated dust within high redshift galaxies, it carries a wealth of information about the processes of star formation therein. Besides, the #uctuations detected in this background light trace the large-scale distribution of star-forming galaxies and, to some extent, the underlying distribution of the dark matter halos in which galaxies reside. The CIB is a thus direct probe of the interplay between baryon and dark matter throughout cosmic times and its unmatched redshift depth complements current and foreseeable optical or near infrared measurements.
Using six regions of the low galactic dust emission with a total area of about 140 deg^2, Planck measured the angular power spectra of CIB anisotropies on angular scales ranging from half a degree to a few arcminutes at 217, 353, 545 and 857 GHz. At all these frequencies, we detect with high significance the clustering of high redshift dusty star-forming galaxies. Combining a new dusty galaxy parametric evolution model with a galaxy clustering model, we obtain a good fit to our data. I will discuss various aspects of these measurements and highlight the unique insights we expect to obtain from them in the coming years, combining Planck and other far-infrared measurements.
Apr. 8, Friday 12:00 pm (INPA Journal Club)
Matt McQuinn, UCB
LBL 50-5026
"Lyman-alpha Forest: 3D"
I will discuss aspects relevant to upcoming Lyman-alpha forest surveys with a dense sample of background sources such as BOSS. In particular, I will discuss the sensitivity of these surveys to large-scale 3D flux correlations, design optimizations for these surveys (relevant for BigBOSS), and some of the physics that these surveys will constrain. My talk will cover some of the results discussed in arXiv:1010.5250 and arXiv:1102.1752.
Apr. 12, Tuesday 1:10 pm
Ludovic Van Waerbeke, UBC
544 Campbell Hall (also videoconferenced to LBL 50F-1647)
"Weak lensing: entering the precision era"
I will present a summary the weak lensing studies performed by the CFHTLenS team on the Canada France Hawaii Telescope Legacy Survey over the past 3 years. CFHTLenS reanalysed the whole CFHTLS survey from scratch and came up with a much better control and understanding of the residual systematics. I will present preliminary results on galaxy-galaxy lensing, cluster lensing, cosmic lensing, and early modified gravity work. Our work on systematics demonstrates that future wide field surveys designed to do lensing will be capable of constraining the matter distribution with unprecedented precision.
Apr. 19 , Tuesday 1:10 pm
Neal Dalal, CITA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"The handwaver's guide to dark matter halos"
Dark matter halos are the endpoints of cosmological structure formation. They play a crucial role in many areas of astrophysics and cosmology. Our understanding of halos is based almost entirely on numerical experiments in N-body simulations, with relatively poor theoretical understanding of what determines halo properties. In my talk, I will try to give a simple way to understand many properties of halos, including their density profiles, their abundance, and their clustering.
Using an extremely simple model, it is possible to match the results of N-body simulations across a wide range of cosmologies, even better than commonly used empirical fitting formulae. Using this approach, we can also predict how halos and their resident galaxies behave in cosmologies that depart from the standard LCDM model, which I will illustrate with some examples.
Apr. 21-23 , Thursday-Saturday Berkeley CMB Lensing Workshop
Apr. 22 , Friday 12:00 pm (INPA Journal Club)
Sudeep Das, UC Berkeley/LBNL
LBL 50-5026 (INPA Room)
"A New VIew of the Cosmic Microwave Background with ACTT"
Over the coming decade, tiny fluctuations in temperature and polarization of the Cosmic Microwave Background (CMB) will be mapped with unprecedented resolution. The Planck Surveyor, the Atacama Cosmology Telescope (ACT), and the South Pole Telescope (SPT) are already making great advances. In a few years, high resolution polarization experiments, such as PolarBear, ACTPol, and SPTPol will be in full swing. While these new arc-minute resolution observations will continue to help constrain the physics of the early universe, they will also be unique in a new way - they will allow us to measure the gravitational lensing of the CMB, i.e., the deflection of CMB photons by intervening large scale structure. CMB lensing will probe the growth of structure over cosmic time, helping constrain the total mass of neutrinos and the behavior of dark energy. In the first part of the talk, I will review the recent progress made with ACT, a powerful tool with new capabilities. In the second part, I will discuss the scientific potential of the CMB lensing signal, its first detection, and its various applications in cross-correlation with other datasets. Finally, I will discuss the upcoming polarized counterpart of ACT --- the ACTPol project, which will have sixteen times better mapping speed than ACT, and will be a premier CMB lensing experiment. I will describe our plans to extract different flavors of science from the ACTPol data, including the cross-correlations with optical lensing and galaxy surveys, such as SDSS, BOSS, DES and LSST.
Apr. 26 , Tuesday 1:10 pm
Kendrick Smith, Princeton
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Large-Scale Structure with non-Gaussian initial conditions"
The observational search for non-Gaussian statistics in the initial conditions of the universe has emerged as a powerful, multifaceted probe of the physics of the early universe. Non-Gaussianity of local type (f_{NL}) has been shown to produce distinctive effects in large-scale structure, resulting in observational constraints which are competitive with the CMB. In this talk we will generalize this picture to the most general local model, which has three parameters f_{NL}, g_{NL}, tau_{NL}. We propose a theoretical framework for predicting the non-Gaussian halo mass function and large-scale clustering of halos, and compare with N-body simulations in this model.

References: Smith & LoVerde, 1010.0055, LoVerde & Smith, 1102.1439, Smith, Ferraro & LoVerde, to appear

March 2011:
Mar. 1 , Tuesday 1:10 pm
Alexie Leauthaud, LBL
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"New constraints on the evolution of the stellar-to-dark matter connection: a combined analysis of galaxy-galaxy lensing, clustering, and stellar mass functions from z=0.2 to z=1"
I will present a joint analysis of galaxy-galaxy weak lensing, galaxy clustering, and the galaxy stellar mass function to constrain the shape and redshift evolution of the stellar-to-halo mass relation from z=0.2 to z=1 using data from the COSMOS survey. Carefully accounting for sample variance and for scatter between stellar and halo mass, we model all three observables simultaneously using a novel and self- consistent theoretical framework. We show that the dark-to-stellar ratio varies from low to high masses, reaching a minimum of Mh/M*=27 at M*=1.6x10^10 Msun. This minimum is noteworthy for galaxy formation because it marks the mass at which the accumulated stellar growth of the central galaxy has been most efficient. We refer to the stellar mass, halo mass, and ratio at which this minimum occurs as the ``pivot stellar mass'', M*_piv, the ``pivot halo mass'', Mh_piv, and the ``pivot ratio'', (Mh/M*)piv. For the first time using homogeneously analyzed data from high to low redshift, we report the detection of downsizing trends for both Mh_piv and M*_piv. However, the co- evolution of these two parameters leaves the pivot ratio roughly constant with redshift at (Mh/M*)piv=27. We discuss this result in terms of galaxy formation models and we show how this coincidence raises the intriguing possibility that the quenching of star formation may have a physical dependance on Mh/M* and not simply on Mh as is commonly assumed.
Mar. 1 , Tuesday 2:30 pm (Galform meeting)
Daniel Stark, Cambridge 544 Campbell Hall
"Unveiling the Nature of Feeble Galaxies in the Early Universe"
Low luminosity galaxies play a fundamental role at high-redshift, dominating the UV luminosity density at z~2-3 and likely producing the majority of energetic photos responsible for reionization. Knowledge of how these galaxies cycle gas into stars, pollute the IGM with metals, and contribute to the ionizing background is crucial to our understanding of the early universe, yet in spite of this, little is known about distant low luminosity systems. In this talk, I will review new efforts to characterize the nature of feeble high redshift galaxies. Through detailed optical and infrared spectroscopy, insight is now being provided into the kinematics, metallicities, and large-scale outflows, and ionizing photon escape fractions of low luminosity galaxies at high redshift. I will discuss preliminary results and prospects for extending this program with new instruments and surveys in the near future.
Mar. 3, Thursday 4:10 pm (Astronomy Colloquium)
Mariska Kriek, Harvard-Smithsonian CfA
1 LeConte Hall
"The Diverse yet Orderly Lives of Galaxies"
At first glance the galaxy population today, and even more so at earlier times, exhibits a huge diversity. However, the well-known correlations between different galaxy properties, such as spatial structure, stellar population, stellar mass, stellar dynamics, and environment suggest that galaxy formation is actually an orderly process. With the recent large photometric and spectroscopic surveys ad new instrumentation on the Hubble Space Telescope, it is now finally possible to study galaxies in a systematic way at earlier times, so that we can see directly how these relations changed over cosmic time and what the physical processes are that drive them. Until very recently, these studies were hampered by the small sizes of spectroscopic galaxy samples, whereas much larger photometric samples lack the required spectroscopic information. I will discuss a novel approach, that makes use of medium-band photometry to perform detailed spectroscopic studies of ~3500 galaxies at 0.5 less than z less than 2.0. By identifying analogous galaxies we construct composite spectral energy distributions, which are of spectroscopic quality. This composite spectrum collection opens up the possibility to efficiently study Halpha and other spectroscopic features for large distant galaxies samples, which would otherwise require extensive near-infrared spectroscopic campaigns. I will show how we have used the composite spectra to study the dimensionality and star formation histories of galaxies. Furthermore, I will discuss many other applications, among which the relation to structural properties, AGN demographics, and dust properties. I will close with an outlook on future spectroscopic capabilities (e.g., MOSFIRE, NIRSPEC on the JWST, WFIRST) for large surveys of distant galaxies, in order to understand their origin.
Mar. 7, Monday 12:10 pm (TAC talk)
Adam Lidz, UPenn
544 Campbell Hall
"Reionization and the Redshifted 21 cm Signal"
One of the primary goals of observational cosmology at present is to detect, and elucidate the nature of, the Epoch of Reionization (EoR). The EoR is a key stage in the history of our Universe when early galaxies and quasars turn on and photo-ionize `bubbles' of neutral hydrogen gas in their surroundings. The ionized bubbles grow and merge, eventually filling essentially the entire volume of the intergalactic medium (IGM) with ionized gas. The most direct way to study the EoR is to use the redshifted 21 cm line, which may ultimately provide full three-dimensional maps of the reionization process. I will describe theoretical work aimed at modeling, and at understanding how to best interpret, future measurements of the 21 cm signal from the EoR. In addition, I will discuss the possibility of using rotational emission lines from the CO molecule to perform an `intensity mapping' experiment during the EoR. The aim of CO intensity mapping is to measure spatial fluctuations in the combined CO emission from many individually unresolved galaxies and use this as a tracer of large scale structure at early cosmic times. I will discuss the feasibility of such measurements, and explain how they might complement future 21 cm measurements.
Mar. 8, Tuesday 1:10 pm
Adam Mantz , Goddard
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Cosmological Results from the Population of X-ray Luminous Galaxy Clusters"
In the past few years, constraints on the growth of cosmic structure have become available from observations of the galaxy cluster population and its evolution. This advance is largely due to the painstaking identification of clusters at redshifts z>0.3 in the X-ray flux-limited ROSAT All-Sky Survey (with ongoing Sunyaev-Zel'dovich and optical surveys not far behind). I will present cosmological constraints obtained from a sample of 238 X-ray flux-selected clusters, which, including the recently released MACS sample, extend to redshift 0.5. The cluster data provide robust constraints on the amplitude of the matter power spectrum as well as the dark energy equation of state (+-0.2 for a constant w model). The ability to trace the growth of structure as a function of time also allows us to test the observed growth rate against that predicted by General Relativity, independent of the background expansion history. Ultimately, this provides a tool for testing alternative theories of gravity and potentially distinguishing them from dark energy models. Finally, I will present constraints on cluster mass-observable scaling relations, a necessary and parallel aspect of the cosmological tests. With new surveys, and with multi-wavelength data becoming available for a growing number of clusters, these kind of analyses are poised to deliver powerful cosmological and astrophysics results.
Mar. 10, Thursday 12:00 pm (RPM)
Marc Kamionkowski, Caltech
LBL 50A-5132
"Beyond Gaussian Fluctuations in the CMB and Galaxies"
The simplest single-field slow-roll (SFSR) models for inflation do a great job of explaining an increasing wealth of data on the distribution of mass in the early Universe and in the Universe today. One of the predictions of SFSR inflation is that primordial perturbations should have a distribution that is precisely Gaussian. However, no theorist believes SFSR models to be any more than toy models, and sooner or later there should be violations, at some level, from the predictions of these simple models. Departures from Gaussianity are one of the possibilities for beyond-SFSR models, and an active effort is now afoot to seek these non-Gaussianities. In this talk, I will discuss (a) some models for non-Gaussianity, (b) ways to detect non-Gaussianity in galaxy surveys, and (c) issues for measurement of non-Gaussianities in the CMB.
Mar. 11, Friday 12:00 pm (INPA Journal Club)
Melissa Graham, UCSB/LCOGT
LBL 50-5026
Type Ia Supernovae with CFHT
I will talk about my work on two surveys for Type Ia supernovae (SNe Ia) with the Canada-France-Hawaii Telescope, the Multi-Epoch NEArby Cluster Survey (MENeaCS) and the Supernova Legacy Survey (SNLS). MENeaCS monitored 60 low redshift, x-ray luminous galaxy clusters with a monthly cadence for two years. We discovered 23 cluster SNe Ia, 4 of which are apparently hostless and likely belong to the population of intracluster stars. I will discuss how we used these SNe Ia to constrain the fraction of light in the intracluster medium, as presented in our first MENeaCS publication (Sand et al. 2011). I will also discuss our recent attempts to characterize star formation and metallicity in our sample of cluster hosts, our preliminary rates measurements, and highlight some additional MENeaCS science. The SNLS, also now completed, discovered ~500 SNe Ia between 0.2
Mar. 15, Tuesday 1:10 pm
Andrei Mesinger , Princeton
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Theoretical and observational insights into reionization and the dark ages "
The dawn of the first generations of luminous baryons signaled the beginning of an important epoch in cosmic history. I will sketch-out three likely stages of this extended process. I will interpret some of the current observational evidence at z~6, focusing on high-redshift quasar spectra. Finally, I will discuss the potential of the redshifted 21cm line in probing not only reionization, but also the dark ages which preceded it. However, to interpret such a bounty of information, we need efficient modeling tools capable of exploring the dauntingly large parameter space, such as our newly developed 21cmFAST.
Mar. 22, Tuesday
spring break, no talk ,
544 Campbell Hall (also videoconferenced to LBL 50A-5131)

Mar. 28, Monday 12:10 pm (CDI Seminar)
Chad Schafer , CMU
1011 Evans Hall
"The Challenge and Potential of Likelihood-Free Inference in Cosmology"
Statistical inference of cosmological quantities of interest is complicated by significant observational limitations, including heteroscedastic measurement error and irregular selection effects. These observational difficulties exacerbate challenges posed by the often-complex relationship between estimands and the distribution of observables; indeed, in some situations it is only possible to simulate realizations of observations under various assumed cosmological theories. When faced with these challenges, one is naturally led to consider utilizing repeated simulations of the full data generation process, and then comparing observed and simulated data sets to constrain the parameters. This talk will discuss the issues faced in implementing such a likelihood-free procedure, with emphasis on how to best make use of the rich data sources available. I will discuss Approximate Bayesian Computation, a procedure originally motivated by similar inference problems in population genetics, and propose frequentist alternatives in the context of a bivariate luminosity function estimation problem.
Mar. 29, Tuesday 1:10 pm
Graca Rocha, JPL/Caltech **postponed**
544 Campbell Hall (also videoconferenced to LBL 50A-5131)

Mar. 30, Wednesday 12:30 pm
Mariangela Lisanti, Princeton
INPA Conference Room, LBL 50-5026
"A Dark Matter Cloud in the Milky Way Sky: Exploring New Possibilities for Substructure "

February 2011:
Feb. 1, Tuesday 1:10 pm
Chris Blake , Swinburne
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"The cosmic distance scale and growth rate at z=0.6 from the WiggleZ Dark Energy Survey"
We present cosmological results from the recently-completed WiggleZ Dark Energy Survey at the Anglo-Australian Telescope. We have obtained spectroscopic redshifts for over 200,000 star-forming galaxies over 1000 sq deg up to redshift z=1. We measure the imprint of baryon acoustic oscillations in the galaxy distribution at the highest redshift to date, and use our detection as a standard ruler mapping the cosmic expansion history. We also exploit redshift-space distortions in the pattern of galaxy clustering to measure the growth rate of cosmic structure across the redshift range z < 1, recovering the first precise measurements in the intermediate-redshift Universe. This combination of cosmic distance and growth measurements allows us to make a powerful self-consistency test of the physical nature of dark energy, spanning the whole epoch for which it is thought to dominate cosmic dynamics.
Feb. 2, Wednesday 11:00 am (INPA Journal Club)
Arman Shafieloo, IEU Korea
LBL 50-5026
Probing Isotropy with SNe Ia Data
The question of the transition to global isotropy from our anisotropic local Universe is studied using the Union 2 catalogue of Type Ia supernovae. We construct a "residual" statistic sensitive to systematic shifts in their brightness in different directions and use this to search in different redshift bins for a preferred direction on the sky in which the SNe Ia are brighter or fainter relative to the 'standard' LCDM cosmology. At low redshift (z<0.05) we find that an isotropic model such as LCDM is barely consistent with the SNe Ia data at 2-3 sigma. A complementary maximum likelihood analysis of peculiar velocities confirms this finding -- there is a bulk flow of around 260 km/sec at z \sim 0.06, which disagrees with LCDM at 1-2 sigma. Since the Shapley concentration is believed to be largely responsible for this bulk flow, we make a detailed study of the infall region: the SNe Ia falling away from the Local Group towards Shapley are indeed significantly dimmer than those falling towards us and on to Shapley. Convergence to the CMB rest frame must occur well beyond Shapley (z>0.06) so the low redshift bulk flow can systematically bias any reconstruction of the expansion history of the Universe. At high redshifts z>0.15 the agreement between the SNe Ia data and the isotropic LCDM model does improve, however, the sparseness and low quality of the data means that we cannot single out any particular model as the preferred cosmological model.
Feb. 3, Thursday 11:00 am (INPA Journal Club)
Zarija Lukic, LANL
LBL 50-5026
"Cluster Cosmology: Opportunities & Challenges"
As the most massive objects in the Universe, and likely the end point in the hierarchical structure formation, galaxy clusters offer unique insight into cosmological growth of structure. Several observational campaigns, including X-ray, optical and microwave telescopes have either just started to collect data on clusters, or will start in the near future. From the theory side, there are two major road blocks for doing cluster cosmology: predicting abundance of clusters for different cosmological models, and finding precise way to measure cluster masses from a given observable. In this talk, I will present our latest results on the mass function from numerical simulations, outlying some future challenges. I will also present a method for classifying clusters as "relaxed" or "merging" in observationally applicable way, and how their fraction can be used for cluster cosmology. I will also show how this classification improves the quality of mass-observable relations. Finally, throughout this talk, I will showcase application of cluster cosmology on two kinds of cluster surveys (X-ray and SZ) and putting constrains on early dark energy models.
Feb. 3, Thursday 12:30 pm (RPM)
Jeremiah Ostriker, Princeton
"Formation of Massive Galaxies"
Looking backwards we have been able to reconstruct from the detailed structure of our own Galaxy and from the fossil evidence derived from the study of nearby galaxies a plausible history of how galaxies formed over the last several billion years. In addition, now that we have a quite definite cosmological model, providing us with a quantitative picture of how perturbations grew from very low amplitude Gaussian fluctuations, we can perform the forward modeling of representative pieces of the universe using standard physical processes to see how well we match our local knowledge and the time-reversed modeling based on the fossil evidence. Finally, we can employ large ground and space based telescopes to use the universe as a time-machine - directly observing the past history of our light-cone. While none of these approaches can give us at the present time results accurate to more than roughly the 5% -> 10% level, a coherent and plausible picture is emerging. Massive galaxies from in two phases. In the first phase, which peaks at redshift z = 6 and ends by redshift z = 2, cold gas streams in making stars in a small (<1kpc) region, but as the stellar mass approaches 1011 Msolar, a hot bubble forms which suppresses further inflow of cold gas. But from redshift z = 3 to the present time, small stellar satellite systems are accreted at typically 10kpc from the center and the size of the total system grows by about a factor of three as the mass doubles. This added, accreted component is mainly comprised of old and low metallicity stars. Energy release from gravitational infall in various forms will terminate star-formation even in the absence of feedback from SN or MBHs. This physical picture seems naturally to lead to the mass, size scale and epoch of galaxy formation and, increasingly, to a first understanding of the detailed internal structure of these systems.
Feb. 3, Thursday 4:10 pm (Astronomy Colloquium)
Dominik Riechers, Caltech
1 LeConte Hall
"Fueling Cosmic Star Formation: High Redshift Star-Forming Galaxies and the Molecular Gas Mass Density of the Universe"
Virtually all major advances in extragalactic astronomy and our understanding of galaxy formation and evolution over the past decade are based on the constraints we obtained on the star formation history and stellar mass density of the universe. These investigations are greatly successful in explaining a range of galaxy properties throughout cosmic times, yet are lacking on fundamental link: a systematic study of the fuel for star formation, the cause for the buildup of stellar mass - i.e., constraints on the molecular gas mass density. I will review the current status of observations of molecular gas in galaxies back to within a few hundred million years after the Big Bang. Based on pathfinder studies with the (Expanded) Very Large Array and the CARMA millimeter array, I will outline the prospects for the upcoming new generation of large observatories (in particular the Atacama Large sub/Millimeter Array) to provide the first solid constraints on the gas mass density of the universe. In synergy with large optical/infrared facilities such as Keck (and in the future, the Thirty Meter Telescope, and the James Webb Space Telescope), this will enable simultaneous studies of the past, present, and future star formation in galaxies throughout cosmic times.
Feb. 4, Friday 12:00 pm (INPA Journal Club)
Rebecca Stanek, Michigan
LBL 50-5026
"Massive Halos in Millennium Gas Simulations: Assembly Bias and Merger Histories"
The distribution of the most massive galaxy clusters is particularly sensitive to cosmological parameters, making them ideal probes of cosmology. I will briefly discuss the success of the Millennium Gas Simulations in matching the X-ray properties of core-excised galaxy clusters. I will then present the merger histories of the total population of massive halos in the MGS. We find that halo properties are correlated over long timescales, and that assembly bias, in the form of halo formation time, imprints itself on the X-ray properties at redshift zero. This may introduce a bias towards clusters with earlier formation times in flux-limited X-ray or SZ surveys.
Feb. 7, Monday 1:10 pm (TAC talk--note time change!)
Phil Hopkins, UCB
544 Campbell Hall
"Gas, Mergers, and Feedback: Driving an Evolving Hubble Sequence"
I'll review how the combination of models that include realistic gas supplies in galaxies, and feedback from massive stars and AGN to maintain those gas reservoirs, have led to huge shifts in our understanding of galaxy formation. In particular, gas-richness may represent the most important determining factor in galaxy evolution through hierarchical mergers, and may resolve a number of decades-old outstanding mysteries. The degree of gas-richness in mergers has dramatic effects on bulge structural properties, stellar populations, mass profiles, and kinematics; models with the appropriate gas content have finally begun to produce realistic galaxies that resolve a number of discrepancies with observations. Evolution in the gas properties of the Universe naturally predicts evolution in the Hubble sequence, giving rise to many of the unique properties of high-redshift galaxies and starbursts. In very gas-rich mergers, expected to occur more and more frequently at high redshifts, gas can qualitatively change the character of mergers, making disks robust to destruction in mergers and explaining the abundance of disks in a Lambda-CDM Universe. Gas-rich mergers also link the brightest starburst and quasar populations with massive galaxies today. I'll close by discussing the next generation of models at the interface between the fields of star formation, AGN, and galaxy formation.
Feb. 8, Tuesday 1:10 pm
Rachel Mandelbaum ,Princeton
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Uncovering the dark side of galaxies"
Attempts to study galaxy formation and evolution suffer from a major difficulty: the fact that galaxies reside in massive dark matter halos that cannot be directly visualized. In this talk, I will present the results of several recent weak lensing studies that have led to a greater understanding of the connection between the components of galaxies that we see (the baryons) and the underlying dark matter field. These results have had direct, and at times surprising or controversial, implications for theories of how galaxies form and evolve. I will also point out some remaining open questions that could (and should!) be addressed with weak lensing in the next generation of wide-field imaging surveys, DES and HSC.
Feb. 9, Wednesday 11:00 am (special RPM)
Rachel Mandelbaum ,Princeton
"Current and future weak lensing cosmology results with wide-field imaging surveys"
Gravitational lensing is a highly useful way to observe the total matter content of the universe, including dark matter. Given the strong observational support for the claim that most of the matter in the universe is dark, weak lensing is therefore a critical part of current and future observational cosmology efforts. In this talk, I will discuss several ways that lensing and other probes of large-scale structure may be used to robustly constrain cosmology. Some very new results from the Sloan Digital Sky Survey (SDSS) will serve as a proof of concept of these methods, which should be a very promising way forward with near-future surveys such as DES and HSC, and eventually LSST, WFIRST, and Euclid.
Feb. 9, Wednesday 12:10 pm (CDI Seminar)
Andy Connolly , University of Washington
1011 Evans Hall
"Reconstructing the Truth"
With the dramatic growth in survey astronomy, mapping the sky over a broad range of wavelengths is becoming a common place activity. Imaging and spectroscopic surveys will soon map large volumes of the universe in unprecedented detail. One of the challenges we now face is how can we reconstruct an underlying model for the universe or find unusual or anomalous sources from inherently noisy and incomplete data streams. In this talk I will discuss how we can approach these questions in the context of reconstructing the mass density field from gravitational lensing and, through comparisons to non-parameteric models, searching for unusual sources within spectral surveys.
Feb. 10, Thursday 8:30 am and following
BigBOSS meeting LBL building 66 Auditorium, by Strawberry Canyon Gate
Feb. 10, Thursday 12:00 pm (INPA talk)
Christel Smith , ASU
LBL 50-5026
"New Nuclear and Weak Physics in Big Bang Nucleosynthesis"
I will discuss the current status of our understanding of primordial nucleosythesis in light of cosmic microwave background observations. I will also discuss the comparison of the predicted primordial light element abundance yields to the observationally determined values. In order to probe possible discrepancies between prediction and observation, I will present big bang nucleosynthesis (BBN) calculations which included new nuclear and weak physics. I will also present some preliminary results using BBN calculations to constrain physics beyond the standard model.
Feb. 10, Thursday 4:10 pm (Astronomy Colloquium)
Doug Finkbeiner , Harvard
1 LeConte
"Galactic Structure: from Fermi to SDSS and Pan-STARRs"
The Milky Way is full of surprises. Our discovery last year of the "Fermi bubbles" is one of the most intriguing results the Fermi Gamma-ray Space Telescope. This bilobular structure shines in 1-50 GeV gamma=rays and spans 100 degrees on the sky We are following up with X-ray observations and refining our models, and expect to learn more about energetic events in the inner Galaxy.
Meanwhile, my group is studying the distribution of dust and stars in the Milky Way using millions of stars from the SDSS and Pan-STARRs surveys. I will present a careful measurement of the dust reddening law in the diffuse ISM using SDSS data, which has led us to recalibrate the SFD dust map. I will also describe future work with Pan-STARRs to explore Galactic structure, including dwarf galaxies and tidal streams.
Feb. 11, Friday 12:00 pm (INPA talk)
Masao Sako , Penn
LBL 50-5026
"Cosmology with Photometric Supernovae"
Future wide-field, deep supernova surveys will discover thousands to tens of thousands of supernova each year, making spectroscopic follow-up observations of all SN candidates a challenging task with existing resources. Studies of supernova properties and cosmology will, therefore, necessitate a photometric determination of the supernova type, cosmological redshift, and the luminosity distance from light curve data alone. I will discuss the feasibility of measuring cosmological parameters with photometric supernovae using data from current large surveys as well as detailed simulations from DES and LSST.
Feb. 14, Monday 11:00 am (RPM)
Doug Finkbeiner, Harvard
LBL 50A-5132
"Dark Matter and Dark Forces: New Approaches to Exploring the Dark Sector"
One of the great challenges of modern physics and cosmology is to identify and characterize dark matter. Direct detection experiments, astrophysical searches, and collider experiments all provide valuable constraints on weak-scale (WIMP) dark matter, but no convincing results (yet). In evaluating these diverse datasets, we must bear in mind that the dark sector could be more complicated than we think, and valuable clues could be hiding in plain sight. My research group has found it fruitful to entertain the possibility that various signals come from WIMPs, and ask what it would take to produce such signals. We have focused especially on a class of models involving a new force of nature that interacts strongly with the dark sector, but only weakly with everything else. I will review the evidence that led us in this direction, and present some generic tests of the idea, accessible to experiment in the near term. These include CMB constraints on energy injection at high redshift, dark boson searches, and delayed-coincidence events in direct detection experiments.
Feb. 15, Tuesday
No talk

Feb. 18, Friday 12:00 pm (INPA Journal Club)
Dragan Huterer, Michigan
LBL 50-5026
"Falsifying Paradigms for Cosmic Acceleration"
How can we rule out whole classes of dark energy models? And what quantities, at what redshift, and with what accuracy, should be measured in order to rule out these classes of models? I present answers to these questions by discussing an approach that utilizes the principal component parametrization of dark energy. I show results based on current data, and future forecasted data from a space-based dark energy mission and Planck. Finally, using the same basic framework I present a quantitative analysis motivated by recent claims that the number of high-redshift, high-mass galaxy clusters (the 'pink elephant' clusters) is in disagreement with the standard cosmological model predictions.
Feb. 22, Tuesday 1:10 pm
Shelley Wright, Berkeley
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Observing Galaxy Evolution: The Exciting Promise of Adaptive Optics Instrumentation"
Adaptive optics (AO) with integral field spectroscopy on 8-10m telescopes has recently become a powerful observational tool for studying galaxies in the early universe (z > 1) at sub-kiloparsec scales. These innovative spectrographs have led to significant scientific achievements and are stimulating the design of future near-infrared instrumentation. I will discuss the development and use of both the latest instruments behind Keck Observatory's AO system and future AO instrumentation on the Thirty Meter Telescope (TMT). In particular, I will present the latest results from Keck OSIRIS observations of spatially resolved optical emission lines (e.g., H, and [N II]) from high-redshift (1 < z < 3) star forming galaxies. These results are part of an ongoing survey to study the dynamics, chemical abundances, and active galactic nuclei (AGN) in early galaxies. The high spatial resolution afforded by AO and the 2D capability of an integral field spectrograph have allowed the discovery of some of the lowest luminosity AGN known at this epoch, and I will discuss their potential impact on high-redshift metallicity studies and galaxy formation. Lastly, I will discuss future AO instrumentation for Keck and the TMT project. I will present sensitivities achievable for AO science with TMT, and highlight TMT's extraordinary potential to probe the dynamics, assembly, and abundances of galaxies in the early universe.
Feb. 24, Thursday 4:00 pm (Astronomy Colloquium)
Aaron Parsons, UCB
1 LeConte Hall
"21 cm Cosmology: Probing the Epoch of Reionization"
The Epoch of Reionization (EoR) --the rapid ionization of the majority of the hydrogen in the universe by the light of the first stars and supermassive black holes--is perhaps the last major phase transition of our universe that remains unexplored. First-generation experiments aiming to measure the 3-dimensional spectrum of reionization fluctuations via redshifted 21cm emission are currently underway. While calibration, foreground removal, and obtaining the requisite sensitivity are all challenging aspects of these efforts, early results suggest that there may imminently be a detection that significantly impacts our understanding of the dominant processes at work during this era.
I will discuss current prospects for detecting the 21cm EoR signal in the context of our recent progress with 16- and 32-antenna deployments of the Precision Array for Probing the Epoch of Reionization (PAPER) in Green Bank, West Virginia, and the Karoo Desert of South Africa. I will also discuss a novel technique for accessing the 3-dimensional power spectrum of reionization, and the impacts of systematics and foregrounds on recent measurements. Finally, I will present our current plans for the Hydrogen Epoch of Reionization Array (HERA) that will supersede all current efforts and enable the direct imaging of reionization structures.
Feb. 25, Friday 12:00 pm (INPA Journal Club)
Bruce Grossan, LBNL
LBL 50-5026
"UFFO & XIGI: Faster Telescopes, Gamma-Ray Burst Astrophysics, Shock Physics, and Maybe Cosmology"
Gamma-Ray Bursts (GRB) are the most energetic explosions in the universe. In the last 20 years, our view of GRBs has changed from poorly understood jumps in count rate to an identified, supernova-related phenomenon that is part of the normal course of stellar evolution. We have barely scratched the surface of what we can learn from GRBs, and they may teach us about topics as diverse as cosmic ray physics, relativistic jet physics, gravity, and cosmology.
Much of the recent progress in understanding GRBs came from new optical observing techniques to augment those in gamma-ray bands. Working with colleagues at the Ewha Womans University in Seoul, we are applying fast-mirror technology to observing the rise phase of GRB optical light curves, previously observed only occasionally. With our micro-electromechanical mirror arrays, we can respond as fast as 1 millisecond after gamma emission. I describe the Ultra-Fast Flash Observatory program, a series of missions to use these rapid mirror technologies to fully explore this new parameter space of GRB observations and science.
Feb. 28, Monday 1:10 pm (TAC talk--note time change!)
Daniel Stark, Cambridge
544 Campbell Hall
"Early Star Forming Galaxies and the Reionization of the Universe"
The events of the first billion years of cosmic history are one of the final frontiers in the quest to trace the history of the Universe from its origins to the present day. Exploration of this uncharted era is driven by the desire to locate and understand the nature of the first stars and galaxies and to characterize their contribution to the reionization of hydrogen. With the installation of the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope, the cosmic frontier has been pushed back to just 500 Myr after the Big Bang, delivering the first census of star formation activity in the reionization ear. Deep Keck spectroscopy of these early systems is now providing insight into the properties of primitive galaxies while simultaneously constraining the progress of reionization. I will summarize the results from these studies, providing possible evidence that reionization is coming to an end in the ~200 Myr between z=6 and z=7, while revealing some tension in the ability of star-forming galaxies to achieve reionization in the required time frame. I will emphasize that in order to properly address the nature of the sources which were responsible for reionization, we must obtain an improved understanding of the physics of the low mass galaxies which dominate the reionization era. To this end, efforts are now underway to characterize the mechanical and radiative feedback of high redshift dwarf galaxies which have been identified via gravitational lensing. I will describe the first results from this program and discuss implications for reionization. I will conclude with a look to the future, discussing how deep surveys with JWST and TMT will transform our understanding of the first galaxies.

January 2011:
Jan. 4, Tuesday 1:10 pm
Cameron McBride, Vanderbilt
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Using LasDamas: What more can we learn from the galaxy distribution?"
Probing the relationship between galaxies and the underlying mass field enables constraints on both models of galaxy formation and cosmology. Results from modern galaxy surveys, such as the Sloan Digital Sky Survey (SDSS), have shown tremendous success, and have helped to usher in the current era of "precision cosmology". However, we are limited in making full use of the observational data. We still have a poor understanding of many complicated non-linear processes which are difficult to model analytically, such as redshift distortions and the messy physics of galaxy formation. In this talk, I will discuss our approach of using a LArge Suite of DArk MAtter Simulations (LasDamas) to mine the scientific content of galaxy data, and better understand the properties of dark matter halos. I will present some early results that could impact cosmological constraints derived using galaxy clusters (e.g. from SZ surveys and Planck) and briefly review some ongoing investigations as well as future directions.
Jan. 18, Tuesday 1:10 pm
Nikolaos Fanidakis, Durham
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Unravelling the properties of active galaxies in hierarchical cosmologies"
I will present a new theoretical model of the formation and evolution of active galactic nuclei (AGN). The calculation is embedded in the GALFORM semi-analytical model which simulates the formation and evolution of galaxies in a Lambda cold dark matter universe. Using this code I calculate the fundamental parameters (mass, spin and accretion rate) that describe the evolution of massive black holes (BHs) hosted at the galactic centres and make predictions for their disc luminosities. The model reproduces the observed optical, X-ray and bolometric luminosity functions of AGN up to z~6. Downsizing in the AGN populations arises naturally from the interplay between two independent accretion channels (the starburst and hot-halo mode). These channels shape the evolution of faint AGN with cosmic time, indicating that the faint end of the AGN LF is dominated by massive BHs experiencing quiescent accretion. The model also reproduces remarkably well the radio loudness of AGN, suggesting that the jet properties of an active galaxy is a natural consequence of the accretion rate and spin characterising its central BH. Based on this model, I make predictions for the clustering of quasars and radio galaxies and explore the statistical properties of dark matter haloes that host active galaxies.

Jan. 19, Wednesday 11:00 am (INPA Journal Club) --note special date and time.
Hendrik Hildebrandt, UBC
LBL 50-5026 (INPA Room)
"Studying Galaxies, Clusters, and Cosmology with Weak Lensing Magnification"
Weak gravitational lensing is one of the major methods to study the dark sector of the Universe on a large variety of mass- and length-scales. So far most observations employed the shear effect of weak lensing. Recently, it has been shown that also the magnification effect can be turned into a powerful, complimentary tool. In this talk I will review the theory behind magnification measurements and highlight advantages and weaknesses of this approach in comparison to shear-based measurements. Furthermore, I will present observations of weak lensing magnification induced by galaxies and galaxy clusters and explain how those will help us to answer open questions in the fields of galaxy-evolution and cluster-astrophysics as well as in cosmology.
Jan. 20, Thursday 4:10 pm (Astronomy Colloquium)
Charlie Conroy , Harvard-Smithsonian, CfA
1 LeConte
"Globular Clusters are Not Simple Systems"
All globular clusters (GCs) studied to date show evidence for multiple stellar populations, in stark contrast to the conventional view that GCs are comprised of stars with a common age and metallicity. In this talk I will summarize the observations and present a plausible scenario to explain them. This scenario requires many dramatic changes to our understanding of GC formation and evolution, including the requirements that 1) at least two epochs of star formation have occurred within all GCs, with the second generation forming from the ejecta of AGB stars associated with the first generation, and 2) GCs contained >10-20 times more stars at birth than they currently possess. The interplay and importance of a variety of physical processes during the first several 10^8 yrs in the life of a GC will be highlighted. I will conclude by discussing the broader implications of these results and selected future observations that promise to shed new light on this exciting problem.

Jan. 21, Friday 12:10 pm (Astronomy Journal Club)
Charlie Conroy , Harvard-Smithsonian, CfA
Campbell 544
"The Stellar Initial Mass Function Is Not Universal"
The stellar initial mass function (IMF) is an essential ingredient in many areas of astrophysics. It is often believed to be 'universal', meaning that it does not vary with environment or epoch, though there is scant evidence for this assumption. In this short talk I will present compelling evidence that the IMF the contains substantially more low mass stars in massive Ellipticals than in our own Galaxy, and therefore is not universal.
Jan. 21, Friday 12 noon (INPA Journal Club)
Alex Vikman , CERN
LBNL 50-5026
"Imperfect Dark Energy of Kinetic Gravity Braiding"
In this talk I will discuss a new class of cosmological scalar fields. Similarly to gravity, these theories are described by actions linearly depending on second derivatives. The latter can not be excluded without breaking the generally covariant formulation of the action principle. Despite the presence of these second derivatives the equations of motion are of the second order. Hence there are no new pathological degrees of freedom. Because of this structure of the theory the scalar field kinetically mixes with the metric- the phenomenon we have called Kinetic Gravity Braiding. These theories have rather unusual cosmological dynamics which may be useful to model Dark Energy and Inflation. I will discuss an equivalent hydrodynamical formulation of these theories, stability and causality for the fluid like configurations and cosmological applications.

Jan. 25, Tuesday 1:10 pm
Andrew Benson , Caltech
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Constraining dark matter phenomenology from Local Group observations"
Recent observational advances in the study of Local Group dwarf galaxies have made these objects invaluable as tests of both galaxy formation and dark matter physics. I will describe new constraints derived from these observations which limit broad classes of dark matter particle candidates (those which decay into another particle that is almost degenerate in mass). I will spend some time discussing the computational techniques needed to address galaxy formation questions such as this and will highlight the new, freely available galaxy formation code, Galacticus, which I have constructed over the past year.
Jan. 26, Wednesday 11:00 am (INPA Journal Club)
Elise Jennings, Durham
LBL 50-5026
"Measuring dark energy using the large scale structure of the Universe"
Forthcoming galaxy redshift surveys will make high precision measurements of the clustering of galaxies on scales in excess of 100/h Mpc. In particular, the distortion of clustering due to the peculiar motions of galaxies and the apparent scale of characteristic features in the galaxy distribution have been proposed as tests of the cosmic acceleration. To obtain meaningful and robust constraints on dark energy, we need to understand any systematics in these measurements. I will present the predictions for redshift space distortions and the growth rate using the first consistent simulation of quintessence dark energy. These calculations demonstrate that despite the large scales considered, the widely used linear theory is not up to the job of modelling clustering in future surveys and, furthermore, its application can lead to catastrophic errors. I will describe a new procedure for analysing redshift-space distortions which is a major improvement over linear theory and will allow us to make better use of the next generation of surveys. The talk will cover the material in the papers: Jennings et al (arXiv:0908.1394, arXiv:1003.4282 & arXiv:1011.2842 )
Jan. 27, Thursday 4:10 pm (Astronomy Colloquium)
Tomasso Treu , UCSB
1 LeConte
"Dark Matter and Black Holes over Cosmic Time"
The standard cosmological model successfully reproduces the properties of the universe on supergalactic scales. However, it is unclear whether it can match the detailed properties of galaxies themselves. In particular, the origin of spheroidal galaxies is currently a point of discord between observation and the standard hierarchical model. For example, the stellar populations, properties, and sizes of massive galaxies are difficult to reproduce by models. Surprisingly, in the past decade it has become clear that supermassive black holes might be an essential ingredient to solve this puzzle: they are found ubiquitously at the centers of spheroidal galaxies and their mass correlates with global properties of the host. Furthermore my work, and that of others, has shown that global properties of spheroidal galaxies also correlate very tightly with those of their dark matter halos. A unified description of dark matter, baryons and black holes seems thus necessary to explain the observed correlations, and could perhaps reconcile the standard model with the conflicting observations. I will present highlights of my observational research program aimed at measuring the evolution over cosmic time of black holes, stars, and dark matter in spheroidal galaxies.
Jan. 28, Friday 10 am (special INPA talk)
Tomasso Treu, UCSB
LBL 50B-4205 (note special room)
"New observational tests of the LCDM (with pesky baryons) paradigm"
Astronomers and cosmologists live in interesting times. According to the standard cosmological model, cold dark matter appears to dominate the dynamics of structure, and yet it is unclear whether it can reproduce the properties of galaxies and clusters at smaller scales. The geometry and dynamics of the universe have been measured to unprecendented precision, and yet most of the energy of the universe is in the form of an unexplained dark energy. I present new observational tests of the standard cosmological model. In particular, I focus on the following questions: are there universal dark matter profiles? Is there dark matter substructure? What is the equation of state of dark energy? I discuss the results, and underscore the crucial need to uderstand the interplay between baryons and dark matter as part of the paradigm. I conclude by discussing future prospects.
Jan. 28, Friday 12 pm (special INPA talk)
Richard Panek,
Building 50 auditorium
"The Real Story of the Search for Dark Energy"
Author Richard Panek will be on hand in person to discuss "The 4% Universe," his new book on the discovery of dark matter and dark energy, at noon this Friday, Jan. 28, in the Building 50 Auditorium. In Panek's words, it's a tale of a "Wild West of the mind, where resources were scarce, competition was fierce, and survival depended on small alliances of convenience#." Publishers' Weekly describes "The 4% Universe" as a "lively story of big personalities, intellectual competitiveness, and ravenous curiosity # as entertaining as it is illuminating." Many of those big personalities are right here at Berkeley Lab.

Jan. 31, Monday 12:10 pm (TAC talk)
Reinabelle Reyes, Princeton
544 Campbell Hall
"Dark energy or modified gravity? Proof of concept of a robust observational test using weak lensing and redshift distortions"
Massive datasets from on-going and upcoming galaxy surveys bring the exciting prospect of distinguishing between dark energy and modified gravity as the origin of the acceleration of the cosmic expansion. In this talk, I will present a proof of concept of a robust and model-independent observational test using imaging and spectroscopy of ~70,000 luminous red galaxies from the Sloan Digital Sky Survey (SDSS). This test combines three different probes of large-scale structure-- weak gravitational lensing, redshift distortions, and galaxy clustering-- to yield E_G, a ratio of galaxy-shear and galaxy-velocity cross-correlations that is sensitive to modifications to general relativity (GR), and moreover, is essentially independent of galaxy bias and the amplitude of matter perturbations. I show that interesting constraints can be obtained even with current data, and highlight the power of future datasets to improve on our 15% level measurement of E_G and enable further tests of modified gravity theories.

Jan. 31, Monday 4:30 pm (physics colloquium)
Matias Zaldarriaga, IAS
1 LeConte Hall
"In The Beginning: Determining The Initial Conditions Of The Big Bang"
We now know that the seeds necessary to form structure in our Universe were in place at the start of the hot big bang phase of our Universe. Thus detailed measurements of the statistical properties of these seeds might shed light on what came before the hot big bang. I will discuss the current state of the subject and recent theoretical results on how best to describe the properties of the initial seeds and what different measurements can teach us about what produced those seeds.

December 2010:
Dec. 2, Thursday 4:10 pm (Astronomy Colloquium)
Rogier Windhorst , ASU
2 LeConte
"How will the James Webb Space Telescope measure First Light, Reionization, and Galaxy Assembly in the post WFC3 era?" We review how the 6.5 meter James Webb Space Telescope (JWST) can measure First Light, Reionization, Galaxy Assembly, building on lessons learned from the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3). We show what combination of area, depth, and wavelength coverage are needed for JWST to detect a sufficient number of First Light objects, and to measure their evolving luminosity function (LF). In detail, JWST will map the epoch of First light through Pop III star dominated objects at redshifts z=8--20, and its transition to the first Pop II stars in dwarf galaxies at z<9. JWST will measure the evolution of the steep faint-end of the dwarf galaxy LF at z=6--12, which likely provided the UV-flux needed to start and finish Hydrogen reionization. We will discuss: 1) what deep JWST images will look like compared to the Hubble UltraDeep Field (HUDF), given JWST's expected PSF performance; (2) simulations of what nearby galaxies observed in the restframe UV--optical by HST would look like to JWST at very high redshifts; (3) quantitative methods to determine structural parameters of faint galaxies in deep JWST images as a function of cosmic epoch to delineate the progress of galaxy assembly; (4) to what extent JWST's short-wavelength performance --- which needed to be relaxed in the 2005 redefinition of the telescope --- will affect JWST's ability to accurately determine faint galaxy parameters; and (5) if ultradeep JWST images will run into the instrumental and natural confusion limits. A new generation of algorithms may be needed to automatically detect, measure and classify objects in very crowded, ultradeep JWST fields.
Dec. 7, Tuesday 1:10 pm
Jonathan Pritchard, Harvard
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Constraining the dawn of structure and the epoch of reionization with the 21 cm line"
The first billion years of the Universe contains the formation of the first galaxies and reionization. This period lies beyond the current observational frontier presenting challenges to theory and observation. Low frequency observations of the redshifted 21 cm line of neutral hydrogen will be key in developing our understanding of this period. In this talk, I will describe two aspects of the 21 cm signal from the period of "cosmic dawn": the global 21 cm signal and 21 cm fluctuations. I will discuss what can be learnt about the first galaxies and reionization from this technique and explore some of the challenges and opportunities ahead for the first observations.

Dec. 10, Friday 12:00 pm (INPA Journal Club)
Joseph Richards, UCB
LBL 50-5026
"Photometric Classification of Astronomical Transients and Variable Stars"
Next-generation photometric surveys need sophisticated statistical tools that accurately classify variable sources for optimal allocation of follow-up resources. I will discuss some of the challenges in building such a classifier, including estimation of class-predictive features from photometric light curves and classification modeling using flexible, robust methods. I describe my work on two classification problems: supernova typing using simulations from the DES Supernova Classification Challenge and variable star classification using light curves from the OGLE and Hipparcos surveys. I will detail my use of cutting-edge statistical methodology such as diffusion maps, random forests and structured classification for these problems.

November 2010:
Nov. 1, Monday 12:10 pm
Dmitry Malyshev, NYU
544 Campbell Hall
"Spherical harmonics of gamma-rays and Galactic dark matter annihilation"
We use the spherical harmonics decomposition of the Fermi gamma-ray map to search for dark matter annihilation in the Milky Way halo away from the Galactic plane. Small L harmonics are most sensitive for extracting a smooth large scale distribution of gamma-rays, such as the gamma-rays produced in DM annihilation at high latitudes in the main halo of our Galaxy. We perform a template fitting in the a_lm space for small L's and find an evidence for a spherically distributed source, additional to typical astrophysical backgrounds. In general, the method of template fitting in spherical harmonics space provides a non-trivial alternative to template fitting in coordinate space and may be especially useful for separating large angular size distributions.
Nov. 2, Tuesday 1:10 pm
Yin-Zhe Ma, Cambridge
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Testing the concordance cosmology at large and small cosmic scales"
In this talk, I am going to question the two apparent observational contradictories to LCDM cosmology---- the lack of large angle correlations in the cosmic microwave background, and the very large bulk flow of galaxy peculiar velocities. On the super-horizon scale, Copi etal. (2009) have been arguing that the lack of large angular correlations of the CMB temperature field provides strong evidence against the standard, statistically isotropic, LCDM cosmology. I am going to argue that the ad-hoc discrepancy is due to the sub-optimal estimator of the low-l multipoles, and a posteriori statistics, which exaggerates the statistical significance. On Galactic scales, Watkins et al. (2008) shows that the very large bulk flow prefers a very large density fluctuation, which seems to contradict to the LCDM model. I am going to show that these results are due to their underestimation of the small scale velocity dispersion, and an arbitrary way of combining catalogues. With the appropriate way of combining catalogue data, as well as the treating the small scale velocity dispersion as a free parameter, the peculiar velocity field provides unconvincing evidence against LCDM cosmology.

Nov. 5, Friday 12:00 pm (INPA Journal Club)
Dovi Poznanski, LBNL/Berkeley
LBL 50-5026
"Cosmology with Type II-P Supernovae, and the High Redshift Rates of Supernovae Ia"
Observations of Type II-P supernovae (SNe) are closing the gap with SNe Ia for cosmological measurements. While SNe Ia are more luminous, SNe II-P are more numerous at high z, and easier to model ab initio. While current SN Ia surveys have reached the limit of systematic uncertainties, SNe II-P offer a different lever arm. This suggests that II-P's may become a prominent tool in the TMT/LSST/JWST era, if proper foundations are laid in time. I will describe our results to date, and our current efforts to further test and apply these methods. Though we see this work as a pathfinder, this project can supply an independent, unequivocal measure of cosmic acceleration. If time permits I will also discuss our latest results on the measurement of the rate of SNe Ia at high redshift, as a probe of progenitor channels.

Nov. 8, Monday 4:00 pm CADIE informal discussion
4th floor LeConte interaction area
Matteo Fasiello,
"Non-Gaussianities from the Effective Theory Approach to Inflation"
We find that curvature-generated interaction terms in the effective inflationary Lagrangian can give important contributions to the amplitude of higher order correlators (e.g. bispectrum, trispectrum); they also generate interesting distinctive features in the form of their shape-functions.
References: arXiv:0709.0293, arXiv:1004.0893, arXiv:1006.5411, arXiv:1010.3993.
Emanuela Dimastrogiovanni,
"Anisotropic non-Gaussianity from primordial vector fields"
I will discuss about models of inflation populated with primordial vector fields and their anisotropic non-Gaussian effects on cosmological correlators at late times.
References: arXiv:0906.4944, arXiv:0909.5621
Nov. 9, Tuesday 1:10 pm
Silvia Galli, Paris-7
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Constraining Fundamental Physics with present and future CMB Experiments"
The recent measurements of the Cosmic Microwave Background (CMB) temperature and polarization anisotropy from experiments such as WMAP, ACBAR and many others have confirmed the theoretical predictions of the standard cosmological model based on inflation, dark matter and a cosmological constant. This not only permits to place stringent constraints on several parameters of the model but also to use it as a new laboratory where to test physical processes in an environment not achievable otherwise. In particular, there is a remarkable agreement between the theoretical description of the recombination process and the data. This fact enables to test any deviation from standard recombination with very high accuracy. Here I focus on the possible presence of an extra injection of energy due to the annihilation of dark matter particles. Interesting model-independent constraints on dark matter properties such as the annihilation cross section and the dark matter particle mass can be determined by using current CMB data. Furthermore, the dependency of the recombination process on the strength of the electromagnetic and gravitational forces enables to put constraints on the variation of the fine structure constant and Newton's gravitational constant. I will present the effect that these phenomena imprint on the CMB and the constraints obtainable using WMAP data and other ground-based experiments. Furthermore, I will show that upcoming data from the Planck satellite and the ACT telescope will improve all the constraints by more than one order of magnitude.
References: arXiv:1005.3808v1, arXiv:1001.3418, arXiv:0909.3584, arXiv:0905.0003v1, arXiv:0905.1808
Nov. 12, Friday 12:00 pm (INPA Journal Club)
Shun Saito , LBNL/UC Berkeley
LBL 50-5026
"Toward unlocking the full potential of BAO information through galaxy surveys"
he baryon acoustic oscillations (BAOs) are powerful tool to constrain cosmic expansion history, and therefore to reveal the nature of dark energy. One advantage in the BAO measurement is that we can in principle measure the angular diameter distance and hubble distance separately. This can be achieved by considering the redshift-space distortion (RSD) which makes galaxy distribution statistically anisotropic. Hence, the precise modeling of the RSD is a crucial task. In this talk, we first discuss the precise modeling of RSD based on perturbation theory. Then we will present observational constraints (though preliminary) on the angular diameter distance and hubble distance, applying our model to the SDSS DR7 power spectra.

Nov. 16, Tuesday 1:10 pm
Yacine Ali-Haimoud, Caltech
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Fast and accurate primordial hydrogen recombination theory"
osmological hydrogen recombination has recently been the subject of renewed attention because of its importance for predicting the power spectrum of cosmic microwave background anisotropies. Correctly interpreting the upcoming data from the Planck satellite in terms of cosmological parameters indeed requires sub-percent accuracy in theoretical recombination histories. Two aspects are crucial to reach such an accuracy. At early times (z >~800), the dynamics of hydrogen recombination is controlled by the slow decays from the n=2 shell to the ground state, through two-photon decays from the 2s state and the highly self-absorbed Lyman alpha transition. Subtle radiative transfer effects must be accounted for in order to correctly calculate the rate of decays to the ground state of hydrogen. At late times, due to the decreasing abundance of free electrons and protons, an accurate recombination history must account for all the recombination pathways, and include excited states of hydrogen up to a very high principal quantum number n > 100. The cold radiation field at late times is not strong enough to maintain the angular momentum substates in statistical equilibrium, and they must therefore be followed separately. The traditional method of solution for the multi-level atom is very time consuming computationally and unpractical for inclusion in fast Markov chains for cosmological parameter estimation. In this talk I will present my recent work on a new method of solution, which allows to account for an arbitrarily large number of excited states, and is 5 to 6 orders of magnitude faster than the previously used method. I will also expose my recent work on radiative transfer effects and my current work on a fast and highly accurate recombination code.
Nov. 16, Tuesday 3:10 pm
Jaime E. Forero-Romero, AIP, Potsdam
501 Campbell Hall
"A Panchromatic View of High-z Galaxies"
Thousands of high-z galaxies have been found at z>4. The theoretical and observational debate on their nature is still open. In this context, I will discuss the rest-frame UV and Lyman-alpha line emission between redshifts 5 and 7 as provided by the analysis of hydrodynamical cosmological simulations. I will present as well results on their stellar content and far infrared properties, summarizing the predictions for the time when MUSE, ALMA and JSWT will be together online.
Nov. 18, Thursday 4:00 pm (RPM)
Ue-Li Pen, CITA
"21 cm cosmology"
Recently, the first cosmological detections of 21-cm large scale structure have been reported. This is the first light from a potentially rich window onto the universe. I will discuss some of the physics that can be obtained from future measurements, from gravity waves to dark energy, and describe observational strategies to achieve that.

Nov. 19, Friday 12:00 pm (INPA Journal Club)
Simeon Bird , Cambridge
LBL 50-5026
"Reconstructing the Matter Power Spectrum From the Lyman-Alpha Forest"
Current analyses of the Lyman-alpha forest assume the primordial power spectrum of density perturbations follows a simple power law form. We have used a large suite of numerical simulations to calibrate a minimally parametric framework for the power spectrum, dropping this assumption. I shall discuss our methods, including our use of the statistical technique of cross-validation to avoid over-fitting the data. Finally, I shall present our results, using current Lyman-alpha data from SDSS, and our forecasts for BOSS data.
Nov. 19, Friday 3:00 pm (SSL colloquium)
Berian James, Dark Cosmology Centre and UCB
SSL Addition conference room
"Inheritance in Galaxies and Clusters" I review the relationship between dark matter haloes and the properties of the objects---principally galaxies and AGN---that form inside them, through the prism of the so-called "halo model." The uncertain constituents of this model are galaxy bias, halo occupation and halo density profile, each of which proves an interesting physics puzzle. I describe our recent progress with them and speculate about the degree to which future surveys can deepen our understanding, as well as how restricted we might be by the underlying framework itself.
Nov. 23, Tuesday 1:10 pm
Neelima Sehgal, Stanford/SLAC
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Cosmology Constraints from Sunyaev-Zel'dovich Galaxy Clusters Detected with the Atacama Cosmology Telescope"
For the first time blind microwave surveys such as the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) are detecting galaxy clusters through the Sunyaev-Zel'dovich (SZ) effect. Counts of galaxy clusters as a function of mass and redshift provide a powerful probe of structure growth and cosmology. I will discuss constraints on the matter power spectrum amplitude, sigma8, and dark energy equation of state, w, from SZ cluster counts detected with ACT.
Nov. 23, Wednesday 12:10 pm (Wednesday Theory Lunch)
Dusan Keres, UCB
544 Campbell
"Gas accretion in galaxies"
Most galaxies are actively star forming at all epochs. However, observations of dense, galactic gas indicate that, at any epoch, there is not enough gas in galaxies to support evolution of star formation activity over time. This suggests that galactic gas is being replenished from the intergalactic medium.
I use fully cosmological simulations of galaxy formation to study the gas supply into galactic component from high redshift to present. At high redshift "smooth" infall of cold filamentary gas dominates the gas supply of all galaxies. This "cold mode accretion" is unlike the accretion in the standard model of galaxy formation in which cooling of the hot halo atmospheres is a source of gas supply to galaxies. Cold mode accretion is a major driver of very active star formation of high-z galaxies enabling such activity to proceed for a significant fraction of the Hubble time. Gas accretion rates at a given halo and galaxy mass decrease with time, causing the drop in star formation rates. At low redshift hot virialized gas can cool in some of the halos, but cold gaseous clouds that form from infalling filaments can dominate gas supply in galaxies such as Milky Way.
In this talk I will describe properties, physics and consequences of cold gas accretion from the intergalactic medium as well as predictions for the observational probes of cold halo gas that can provide strong constraints on the models. I will also discuss remaining open questions and future directions in this field, including new computational methods and observations with upcoming facilities.

Nov. 29, Monday 12:30 pm - 4:00 pm
AAS Astro2010 Town Hall meeting
Madrone Room, Martin Luther King, Jr. Student Union (ASUC)

Schedule at http://cips.berkeley.edu/events/townhall/index.html
Nov. 30, Tuesday 11:00 am (CDI Seminar)
Tamas Budavari , Johns Hopkins
1011 Evans Hall
"Bayesian Inference from Photometric Surveys" With the upcoming survey telescopes just around the corner, the statistical and computational challenges of astronomy are more prominent than ever. We will discuss some of the fundamental issues that are at the core of all photometric analyses. A powerful Bayesian approach is introduced for cross-identifying astronomical sources, which is extendable, e.g., to incorporate models of spectral energy distributions, to accommodate the proper motion of stars, or to match transient events in space and time. Probabilistic inferences open up new possibilities for determining properties of celestial objects based on their photometric observations. Constraints on photometric redshifts and other physical parameters in the more general inversion problem are derived from first principles that also point us toward the next steps.
Nov. 30, Tuesday 1:10 pm
KG Lee, Princeton
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"A Novel Lya Forest Statistic and SDSS Constraints on the IGM"`
The Lyman-alpha Forest is an important probe of the inter-galactic medium (IGM), which comprises >90% of baryons at high redshifts and is the reservoir for galaxy formation. HeII reionization at z~3 is predicted to be the dominant process in regulating the properties of the IGM below that redshift. I will introduce a new statistic, the threshold clustering functions, which can detect thermal inhomogeneities arising from HeII reionization when applied to SDSS data. I will also discuss some of the systematics involved, and quantify the ability of this statistic to distinguish between different toy models of the IGM.

October 2010:
Oct. 1, Friday 12:00 pm (INPA Journal Club)
Weidong Li, Berkeley
LBL 50-5026
"Nearby Supernova Rates from the Lick Observatory Supernova Search (LOSS)"
In this talk I will present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). We have obtained 2.3 million observations of ~15,000 sample galaxies over an interval of 11 years (March 1998 through Dec. 2008). We considered 1036 SNe detected in our sample and used an optimal subsample of 726 SNe (274 SNe Ia, 116 SNe Ibc, 324 SNe II) to determine our SN rates. This is the largest and most homogeneous set of nearby SNe ever assembled for this purpose, and ours is the first local SN rate analysis based on CCD imaging and modern image-subtraction techniques. I will talk about the properties of our sample galaxies, the derivation of the luminosity function of SNe Ia from a complete sample to help with the rate calculations, and the correlations between SN rates and their host galaxy properties. We find that there is a significant rate-size relation: the galaxies of smaller sizes (luminosities or masses) have bigger SN rates (after normalized by its size). I will discuss the implication of this relation and whether it is connected to the star formation histories of the sample galaxies. I will also discuss the popular two-component ("prompt" and "delayed") model for the SN Ia rates and what we have learned from our search.

Oct. 5, Tuesday 1:10 pm
Anthony Pullen, Caltech
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Search for Anisotropic Power in Large Scale Structure"
Statistical anisotropy in the large scale structure of the Universe is now more than just a theoretical curiosity, but also a possible observational artifact. In this talk, I describe a search for a violation of statistical isotropy in the form of a primordial power spectrum with quadrupolar anisotropy. We probe this possibility using a sample of photometric luminous red galaxies measured by SDSS, which is remarkably different from the usual searches in the CMB. Through this procedure we place limits on the amount of quadrupolar anisotropy in the Universe. I conclude by comparing these limits to those set by the CMB.

Oct. 6, Wednesday 12:10 pm (Wednesday Theory Lunch)
Chris Hayward, Harvard
544 Campbell
"Do submillimeter-selected galaxy number densities provide evidence for a top-heavy IMF?"
I will describe our efforts simulating dusty galaxies through a combination of Gadget-2 (Springel 2005) hydrodynamical simulations and Sunrise (Jonsson 2006, Jonsson et al. 2010) dust radiative transfer. The talk will focus on our model for submillimeter-selected galaxies (SMGs), a population of high-redshift (z ~ 1-5), dusty ULIRGs. SMGs are of particular interest because theoretical models have had difficulty reproducing their observed number densities unless they utilize a top-heavy IMF (Baugh et al. 2005). I will show that our model can reproduce the observed number densities without resorting to IMF variation. I will also discuss the relationship between submm flux and star formation rate, showing why starbursts are not as efficient at boosting submm flux as one might naively think. Finally, I will touch on the relationship of SMGs to other dusty galaxy populations.

Oct. 8, Friday 10:00 am due to runaround (INPA Journal Club)
Renee Hlozek, Oxford
LBNL 50-5132 (Director's conference room)
"The Atacama Cosmology Telescope: Spectrum and parameters from the 2008 South Survey at 148 and 218 GHz"
The Atacama Cosmology Telescope (ACT) has mapped the microwave sky to arcminute scales. We will present the spectrum at 148 and 218 GHz from the 2008 season of the Southern Survey of the Atacama Cosmology Telescope. Improved map-making and efficient spectrum estimation allow us to recover the second through seventh acoustic peaks, and provide independent confirmation of the LCDM paradigm. After briefly discussing the telescope and tests of the spectra, we will describe constraints on both primary cosmological parameters and secondary parameters from the small-scale power spectrum, including diffuse SZ emission and foregrounds.
Oct. 12, Tuesday 1:10 pm
Cora Dvorkin, Chicago
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Model-Independent Constraints on Inflation from the CMB"
I introduce a general method for constraining the shape of the inflationary potential from Cosmic Microwave Background (CMB) temperature and polarization power spectra. This approach relates the CMB observables to the shape of the inflaton potential via a single source function that is responsible for the observable features in the initial curvature power spectrum. The source function is, to an excellent approximation, simply related to the slope and curvature of the inflaton potential, even in the presence of large or rapidly changing deviations from scale-free initial conditions. Oscillatory features in the WMAP temperature power spectrum have led to interest in exploring models with features in the inflationary potential, but such cases are typically studied on a case-by-case basis. This formalism generalizes previous studies by exploring the complete parameter space of inflationary models in a single analysis. I will present results from a Markov Chain Monte Carlo likelihood analysis of WMAP 7-year and other data sets that probe the inflationary potential both at large and small scales, and I will discuss constraints from upcoming high-sensitivity experiments.

Oct. 12, Tuesday 4:00 pm (RPM)
Alex Szalay, Johns Hopkins
LBL 50A-5132
"Redshift-Space Distortions of Baryon Acoustic Oscillations"
The talk will present recent results from analyzing the SDSS Main Galaxy Survey. We will discuss the impact of using unusual geometries in computing the galaxy correlation function. We show that redshift-space distortions can substantially sharpen the BAO peak in directions close to the line of sight.
Oct. 13, Wednesday 12:10-1:00 pm (Wednesday Theory Lunch)
Brad Tucker, Mt. Stromlo
Campbell 544
"Looking Beyond the Optical to Help Supernova Cosmology"
The use of type Ia supernova (SN Ia) as standard candles has shifted from testing whether the Universe is accelerating to determining the dark energy equation of state to better than 10% to distinguish between various cosmological models. However, we still lack a clear understanding of the SN Ia progenitor systems, and their use in cosmology has provided a variety of problems preventing us from reaching these goals. By investigating the host galaxies of type Ia supernova, we can gain important insights into the supernova while improving our determination of the dark energy equation of state. In order to maximize our knowledge, we must look outside the optical wavelengths, namely to the ultraviolet and infrared as important information about the galaxy is contained in these wavelengths. I will show current results using Far-UV to Near-IR observations of both nearby and high redshift supernova surveys and how our understanding of these systems has changed form purely optical wavelengths and will only improve with future planned observations.
Oct. 13, Wednesday 1:30-3:00 pm (special informal discussion)
Atsushi Taruya, Takahiro Nishimichi, Tokyo & IPMU, respectively
LBL 50A-5132
"Signature of primordial vector modes on large-scale structure" (Taruya)
There may exist vector perturbations produced during the early phase of the universe. Although these are now thought to be minor components in cosmology, a detection of vector modes would pose an interesting opportunity to constrain the early-universe physics. In this talk, we discuss methods to detect vector modes from the observation of large-scale structure.
"Shape of Halo Bispectrum from Non-Gaussian Initial Conditions in Cosmological N-body Simulations"(Nishimichi)
will show you the halo bispectrum measured from our N-body simulations starting from non-Gaussian initial conditions. We nd that the halo bispectrum exhibits a strong dependence on the shape and scale of Fourier space triangle near squeezed congurations at large scales. This dependence is, however, different from what is seen in the matter bispectrum. The amplitude of this contribution roughly scales as f_nl^2, which is consistent with the peak bias prediction by Jeong & Komatsu. We systematically investigate the dependence with varying redshifts and halo mass thresholds. It is shown that the f_nl dependence of the halo bispectrum is stronger for more massive halos at higher redshifts. This feature can be a useful discriminator of ination scenarios in future deep and wide galaxy redshift surveys.
Oct. 14, Thursday 4:10 pm (Astronomy Colloquium)
Rob Simcoe, MIT
2 LeConte Hall
"Early Galaxy Formation and the Chemical Enrichment of Intergalactic Matter"
Heavy elements have been detected in tenuous intergalactic gas at essentially all observed redshifts. This suggests that nascent galaxies expelled some fraction of their interstellar material starting very early in the history of the universe. The physical process that distributed these metals may also govern many aspects of the galaxy formation process itself. I will review the status of intergalactic chemical abundance measurements and describe new efforts to push these techniques beyond redshift 6, using the newly commissioned FIRE infrared spectrometer at the Magellan telescopes. At these epochs, we may begin to witness nucleosynthetic byproducts from the generation of galaxies that reionized the universe.
Oct. 15, Friday 12:00 pm (INPA Journal Club)
Jianjun Chen, Zhongrui Bai, Guangwei Li , NAOC
LBNL 50-5026 (INPA common room)
"LAMOST Telescope and Its 2D Pipeline"
LAMOST is a 4-meter reflecting Schmidt telescope with 5 degree field of view and 4000 fibers. Now it is running in its commissioning phase. We will introduce the specifications, science goals, recent tests of LAMOST telescope, and in particular the 2d pipeline and a new algorithm for 2D spectral extraction.
Oct. 15, Friday 12:10 pm (Astronomy Journal Club)
Steve Rawlings, Oxford
Campbell 544
"The Square Kilometre Array: Cosmic Origins and Fundamental Physics"
I will review the phased approach to SKA development and construction that delivers a series of transformational results starting now with experiments with the precursors and pathfinders, and utilising observations at other wavebands as appropriate to the main science drivers. The SKA has the potential to answer profound questions like: when did the first stars form? what caused the re-ionization of the Universe? is dark energy different from the cosmological constant? what is the neutrino mass? is there a gravitational wave background due to merging supermassive black holes?

Oct. 19, Tuesday 1:10 pm
Jean-Rene Gauthier, Chicago
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Constraining the gas content of dark matter halos"
Characterizing the structure and evolution of the cool gas in dark matter halos is a key element in current models of galaxy formation. Several physical mechanisms have been introduced to explain the origin of the cool, T 1e4 K gas in dark matter halos of normal galaxies. Some of these mechanisms include cold accretion on dark matter halos (e.g. Keres et al. 2009), gas-rich galaxy mergers (e.g. Wang et al. 1993), and starburst driven outflows (Weiner et al. 2009). Unfortunately, because of the lack of observational constraints on the cool, gaseous envelope of galaxies, the origin of the gas remains a debated subject. In this talk, I will present a series of empirical constraints on the cool gas content of dark matter halos at z 0.5 with a particular focus on massive, 10^13 Msun/h halos. First, I will present the outcome of a clustering analysis done on a population of MgII absorption doublets found in the spectra of SDSS QSOs. Second, I will present the results of a census of cool gas in the halos of Luminous Red Galaxies and its implications for current models of galaxy formation.

Oct. 22, Friday
Cosmology in Northern California
Oct. 25, Monday 12:10 pm (TAC seminar)
Ji-hoon Kim, Stanford/SLAC
544 Campbell Hall
"Galaxy Formation with Self-consistently Modeled Stars and Massive Black Holes: Towards An Unabridged Understanding of Their Coevolution"
While there is now an abundance of evidence suggesting the coevolution of galaxies and their embedded massive black holes (MBHs), a comprehensive astrophysical understanding which incorporates both galaxies and MBHs is still missing. To tackle the highly nonlinear process of galaxy - MBH interaction, a self-consistent numerical approach is imperative. Yet, most of the simulations so far have only used approximated ways of modeling stars and MBHs with parametrized sub-resolution recipes. In order to simulate the actual physical processes, I develop a fully self-consistent galaxy formation simulation integrating the growth of galaxies and MBHs in one comprehensive framework. The high-resolution adaptive mesh refinement (AMR) code Enzo not only models the formation and feedback of molecular clouds at a spatial scale of 15.2 pc, but also simulates the gas accretion onto a MBH and two major channels of MBH feedback: radiative feedback (monochromatic X-ray photons followed by full 3D ray tracing) as well as mechanical feedback (bipolar jets resolved in shock-capturing AMR). I will present the first results from the investigations on (1) the coevolution of a 1e12 Msun galaxy and its embedded MBH at z~3, and (2) the binary mergers of two disk galaxies of 2e11 Msun each. I will also discuss the implications of my improved numerical tool and future projects.

Oct. 26, Tuesday 1:10 pm
Masatoshi Shoji, Austin
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Massive Neutrinos in Cosmology: Toward a Measurement of the Absolute Neutrino Masses"
By measuring the total mass of all neutrino species, we would make great progress toward measuring absolute neutrino masses, one of the long standing problems in physics. A galaxy survey is a powerful tool to measure the total masses of neutrinos, especially when we exploit the information in the power spectrum in the mildly non-linear regime. In order to understand matter clustering at the mildly non-linear regime, we have extended the single fluid higher order perturbation theory (1-loop SPT) to include an additional fluid component with non-negligible pressure, and solved the multi-fluid system self-consistently up to third order in density contrast for each fluid component. We have also examined the applicability of the fluid approximation for a range of neutrino masses, redshifts and wavenumbers. Roughly speaking, the fluid approximation is accurate if neutrinos were already non-relativistic when the neutrino density fluctuation of a given wavenumber entered the horizon. We find that the fluid approximation is accurate at few to 25% for massive neutrinos with 0.05
Oct. 27, Monday 12:10 pm (Theory lunch seminar)
Claude-Andre Faucher-Giguere, UCB
544 Campbell Hall
"Probing the Accretion of Gas onto Galaxies: Opportunities and Pitfalls"
Galaxies must continuously accrete gas from the intergalactic medium in order to sustain their observed star formation rates. How this accretion proceeds is a fundamental problem in galaxy formation, as it determines how rapidly galaxies can grow as a function of mass and redshift, as well as the efficiency of preventive feedback processes. While theoretical work predicts that galaxies acquire most of their baryons via the "cold mode", observations have so far not found clear traces of the cold streams. I will discuss results from a research program aimed at robustly quantifying the observational signatures of the cold mode, both in emission and in absorption. In doing so, I will highlight some of the theoretical challenges involved, which can lead to incorrect predictions and jeopardize this unique opportunity to test a physical prediction of galaxy formation if not addressed properly.

September 2010:
Sep. 7, Tuesday 1:10 pm
Michael Brown, Monash
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Does every early-type galaxy host a radio AGN?"
The best known examples of early-type galaxies, including M87 and NGC 5128, host radio active galactic nuclei (AGN). These radio AGNs are clearly interacting with their surrounding environment, and it is quite plausible that they are playing a significant role in regulating star formation within their host galaxies. Do radio AGN play this role in all early-type galaxies? To investigate this, I have studied the 1.4 GHz continuum emission from early-type galaxies with apparent magnitudes of K<9. The median radio luminosities of early-type galaxies increase rapidly as a function of stellar mass, although at a fixed stellar mass the spread in radio luminosity is extremely large. The most massive early-type galaxies have measured fluxes that are consistent with all of these galaxies being radio sources.

Sep. 10, Friday 12:00 pm (INPA Journal Club)
Sanghamitra Deb, LBNL
LBL 50-5026
"Probing Galaxy clusters with Gravitational lensing"
lusters of galaxies are among the richest astrophysical objects. To truly understand them, we need a detailed study of the relationship between observables and the underlying dark matter distribution. Gravitational Lensing is a direct probe of dark matter. I will talk about using lensing to map the mass distribution of galaxy clusters. In my thesis I have developed a new mass reconstruction technique "Particle Based Lensing (PBL)". This method optimally combines lensing information of varying signal-to-noise, and makes no assumptions about the relationship between mass and light. I have applied PBL to several clusters, including The super-cluster A901/902 and A1689. For A901/902, I have measured the ellipticity of the distribution of light and dark matter. A1689 is one of the richest clusters known, and has significant substructure at the core. I find that the dark matter distribution is significantly clumpier than indicated by X-ray maps of the gas. I will also describe an ongoing project involving a sample of 20 clusters to calibrate the mass-temperature relation. I aim to use this sample to do strong+weak lensing analysis and compare the resulting dark matter distribution to the gas distribution from X-rays and SZ effect.

Sep. 14, Tuesday 1:10 pm
Hao-Yi Wu, Stanford
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Precision Cosmology from Optical Galaxy Cluster Surveys: Observational and Theoretical Challenges"
Dark energy constraints from future optical galaxy cluster surveys will depend on how various systematic errors are controlled. I will first focus on the observable-mass distribution, discussing self-calibration and follow-up observations for constraining cluster mass. I will then talk about theoretical uncertainties, discussing how precise calibrations of the dark matter halo mass function, bias function, and assembly history using N-body simulations will impact precision cosmology.

Sep. 20, Monday 12:10 pm (TAC seminar)
Oliver Hahn, KIPAC/Stanford
544 Campbell Hall
"Galaxy Formation in Cosmic Context"
A major challenge in cosmological simulations is to bridge the gap between cosmic sample variance - which requires a large volume to be simulated - and sufficient resolution in single objects. I present a new code to generate multi-scale adaptive mesh initial conditions which allows to face this challenge and enables us to study cosmic structure formation at high local resolution at variance with cosmic environment. I will also discuss an application of this technique in a simulation to study the orientation of disc galaxies with respect to their surrounding large-scale structure.

Sep. 20, Monday 4:30 pm (Physics colloquium)
Marc Kamionkowski, Caltech
1 LeConte
"Is the Universe (Statistically) Isotropic?"
Inflation predicts that the Universe is homogeneous and isotropic---that is, it is the same everywhere and in every direction. Cosmological homogeneity and isotropy are generally *assumed* to be true, but this is a prediction that can be tested quantitatively. I will first discuss some new tests of statistical homogeneity and isotropy, and related tests for a preferred cosmological frame. I will then review briefly some recent evidence that may show a departure from homogeneity and present a theoretical model that may account for this anomaly. In the last few minutes, I may speculate wildly about the pre-inflationary Universe.
Sep. 21, Tuesday 1:10 pm
Greg Martinez, Irvine
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"A Bayesian Analysis of a Milky Way ultra-faint satellite"
With the advent of SDSS the number of known Milky Way satellites has more than doubled. There new members, such as Segue 1, are extremely optically faint. Accurate mass measurements require careful analysis of velocity data. Here I describe the analysis of the multi-epoch velocity measurements of Segue 1 to determine its intrinsic velocity dispersion. Our method includes a simultaneous Bayesian analysis of both membership probabilities and the contribution of binary orbital motion to the observed velocity dispersion. Our analysis strongly disfavors the possibility that segue 1 is a bound star cluster. The inferred dark matter density is one of the highest measured, making Segue 1 a prime source for indirect dark matter detection. I will discuss the possibility of indirect detection in the context of SUSY models.
Sep. 24, Friday 12:00 pm (INPA Journal Club)
Jason Steffen,FNAL
LBL 50-5026
"Results of the GammeV-CHASE probe for chameleon dark energy"
A scalar field is a favorite candidate for the particle responsible for dark energy. However, few theoretical means exist that can simultaneously explain the observed acceleration of the Universe and evade tests of gravity. The chameleon mechanism, whereby the properties of a particle depend upon the local environment, is one possible avenue. I present the results of the Chameleon Afterglow Search (CHASE) experiment, a laboratory probe for chameleon dark energy. CHASE marks a significant improvement other searches for chameleons both in terms of its sensitivity to the photon/chameleon coupling as well as its sensitivity to the classes of chameleon dark energy models and standard power-law models. Since chameleon dark energy is virtually indistinguishable from a cosmological constant, CHASE tests dark energy models in a manner not accessible to astronomical surveys.
Sep. 27, Monday 12:10 pm (TAC seminar)
Mike McDonald, Maryland
544 Campbell Hall
"New Constraints on the Formation of Optical Filaments in the Cool Cores of Galaxy Groups and Clusters"
We present results from a survey of cooling flow clusters and groups covering three orders of magnitude in mass, and 1-2 order of magnitude in temperature and mass deposition rate, aimed at explaining the presence and morphology of warm, ionized gas in the cool cores of galaxy groups and clusters. Using the Maryland-Magellan tunable filter on the Baade 6.5-m telescope at Magellan we have taken a census of these mysterious Halpha filaments with unprecedented depth and resolution. These data have been supplemented with archival X-Ray (Chandra), UV (HST, GALEX, XMM-OM), near-IR (2MASS) and radio (VLA) observations. Armed with the most detailed picture of the warm, ionized gas in cooling flow clusters to date, we investigate the possible mechanisms for producing the observed morphologies (buoyant bubbles, runaway cooling, interaction with satellites, etc) as well as possible ionization mechanisms (young stars, heat conduction from the ICM, collisional heating from cosmic rays, etc). Additionally, we determine the effect of environment on the formation of ionized filaments by considering the correlation of Halpha filaments with the global mass, temperature and gas fraction of the system. Our results offer exciting new constraints, both quantitative and qualitative, for the latest models of cooling flow clusters.

Sep. 28, Tuesday 1:10 pm
Matt Auger, UCSB
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Baryonic and Non-Baryonic Dark Matter in Massive Galaxies"
It is well-established that massive galaxies are embedded in cold dark matter halos. However, little is known about the dark matter at the centers of these galaxies, including how much dark matter is baryonic (e.g., low mass stars or stellar remnants) or how the cold dark matter is distributed in the center of these galaxies. This, in turn, has significant consequences for understanding the luminous structure and evolution of galaxies. I will present recent results that use a variety of mass tracers to show that massive galaxies may have more baryonic dark matter than is conventionally thought, the stellar initial mass function of these galaxies may be non-universal, and standard descriptions for the central cold dark matter distribution in galaxies are inadequate.

July 2010:
July 9, Friday 12 noon (INPA Journal Club)
Davide Pietrobon, JPL/Caltech
LBNL 50-5026
"Extracting cosmological information effectively"
Astrophysical data sets are becoming more and more accurate making possible to address fundamental questions concerning how the Universe began and which processes governed its evolution. The answers to these questions point towards new physics which either takes place at very high energy scales, for instance inflation, or may require a revision of the Einstein theory of gravity. The impressive improvement of the quality of the data must be followed by a refinement of the tools we apply to analyze them, in order to be able not only to control all the systematics, but also to disentangle the primordial cosmological signal we are interested in from the emission of our Galaxy, like synchrotron and free-free radiation or thermal dust emission. We have been developing a tool, needlets, extremely suitable for the analysis of 2-dimension signal on the sphere. Usually such studies are carried out either by looking at the actual signal on the sky in a given direction or by taking its spherical harmonic transform. Most the times both approaches are combined to optimize the result. This procedure con be difficult and not very efficient if only a portion of the sky is observed. To solve this problem a wavelet-based approach has been proposed, which combines a multi-scale study together with a local analysis of field. Needlets are a peculiar type of wavelets whose scaling and localization properties are analytical determined and very sharp. This translates into very small correlation between the functions which is crucial for high level statistical analysis. We applied needlets to the WMAP CMB temperature maps to test the Gaussianity assumption of cosmological perturbations and the investigate dark energy properties.

August 2010:
Aug. 26, Wednesday 12:10 pm (Theory Lunch)
Shy Genel, MPE
544 Campbell Hall
"On the formation of gas-rich star-forming disks at z~2: cosmological 'zoom-in' SPH simulations"
Star-forming galaxies at redshift ~2 are observed to be very different from local late-type galaxies in several respects: their (specific) star-formation rates are a factor of ~10 higher, their morphologies are highly irregular and clumpy and their gas is probably much more turbulent. I will present cosmological N-body/SPH simulations with 'zoom-in' initial conditions and resolution of <~100pc that reproduce many of the properties of that observed galaxy population. The modeled galaxies are thick and marginally-unstable gas-rich disks with large and massive transient star-forming clumps. I will discuss the critical role of stellar feedback in their formation and several gaps that remain in our understanding of their evolution.

Cosmology Seminars in Previous Years

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