Upcoming and Previous Seminars

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 2008-2009
The Physics/Astronomy C290C series consists of the LBNL-Physics-Astronomy Cosmology seminars held Tuesdays 1:10-2:00 pm in room 544 Campbell Hall (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:

Past Months
May 2009:
May 5, Tuesday 1:10 pm
Alexey Vikhlinin, CfA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"The present and the future of growth of structure studies with galaxy clusters"
I will present Chandra observations of ROSAT-selected galaxy clusters which allow us to reconstruct the evolution of the galaxy cluster mass function between z = 0 and z = ~0.7. The statistical and systematic errors in this measurement are sufficiently small, so that we can now confidently observe how the growth of structure at z < 1 is suppressed by the effects of dark energy; we can also improve constraints on the dark energy equation of state and the mass of light neutrinos. I will also discuss strategies for improving the accuracy of the cluster mass function measurements so that they provide useful cosmological information in the JDEM era.
May 5, Tuesday 3:40 pm
Eric Linder,UCB
402 Old LeConte
"Cosmological Constant Behavior in DBI Theory"
May 7, Thursday 4:10 pm (Astronomy Colloquium)
Lisa Kewley, Hawaii
1 LeConte Hall
"The Cosmic Star Formation and Metallicity History of Galaxies"
Observing the star formation rate and metallicity since the earliest times in the universe is crucial to understanding galaxy formation and evolution. Current cosmic star formation history studies are plagued by significant discrepancies between star formation rate estimates and different wavelengths. I apply the new generation of stellar population synthesis and photoionization models and show that metallicity is key to resolving the star formation rate discrepancies. Although the cosmic star formation history has been studied extensively, our understanding of the metallicity history of star-forming galaxies is still largely theoretical. I present the results of our large ongoing observational investigation into metallicity history of star-forming galaxies between 01. I compare our observed metallicity history with predictions from cosmological hydrodynamic simulations, and discuss the future directions for our star formation and metallicity history research. The goal of this research program is to gain a simultaneous observational understanding of the gas-phase metallicity and star formation history of galaxies between 0
May 12, Tuesday 1:10 pm
Jorge Moreno, Haverford
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Halo merger rates and quasars"
Understanding the growth of supermassive black holes at the center of most galaxies is a quite interesting challenge today. It is believed that their growth is enhanced by galaxy mergers, in which cold gas is driven to the center of the remnant. We present an analytic model where quasars are triggered by major mergers of dark matter haloes. Theoretical merger rates beyond the standard EPS prescription, and compatible with the Millennium Simulation, are used. The impact of mergers on the luminosity function is discussed, along with the impact of varying the accretion parameters involved. Shutdown at low redshifts is addressed as well.
May 19, Tuesday 1:10 pm
Andy Connolly, Washington
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"From Physics to Photons and Back: Scaling Science in the Era of the LSST" (please note, 90Mb)
The new generation of astronomical surveys such as the Large Synoptic Survey Telescope provide many opportunities for constraining cosmological models. The size and dimensionality of these data sets, Petabytes per year, present interesting challenges for how we undertake this science. In this talk I will discuss new ways of analyzing data streams from large astronomical surveys including the development of high fidelity simulations to test the scientific constraints that LSST can deliver, ways for reducing the complexity of data to simplify analyses (when dealing with millions of sources each with hundreds of measured attributes) and how to build off the techniques used to index the internet to scale the science we do today to the data sets we expect to work on in the coming decade.
May 26, Tuesday 1:10 pm
Meir Shimon,
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"CMB and Fundamental Physics"
The small temperature anisotropy and polarization of the cosmic microwave background (CMB) radiation have been the target of numerous earth-based, baloon-born and satellite missions in the last two decades. Upcoming CMB experiments, equipped with higher sensitivity and angular resolution, will provide us with higher fidelity probes of the CMB polarization state and secondaries, such as comptonization of the CMB by the Sunyaev-Zeldovich (SZ) effect. The CMB is essentially a snapshot of the universe at recombination and carries valuable information about a much earlier process, cosmological inflation. Secondary effects that took place much later, at redshifts of a few, such as gravitational lensing of the CMB by the intervening large scale structure and the SZ effect, provide us with cosmological bounds on neutrino masses and chemical potentials as well as the dark energy equation-of-state. Rotation of the CMB polarization-plane, due to non-standard coupling of the electromagnetic field to other scalar fields, 'cosmological birefringence', can be used to set limits on the axion mass and coupling to electromagnetic fields. Finally, spectral distortions in the SZ effect can be used to constrain non-standard scalings of the CMB temperature with redshift.
April 2009:
Apr. 2, Thursday 4:00 pm (RPM)
Saul Perlmutter, Robert Cahn, David Schlegel , (LBNL)
LBL 50A-5132
"An Informal Discussion of JDEM"
Apr. 6, Monday 3:10 pm (RAL seminar)
Don Backer , UCB
544 Campbell Hall
"PAPER - Precision Array to Probe the Epoch of Reionization"
The first stars reionized the intergalactic medium that became neutral after the microwave background decoupled from matter. The 21cm line of hydrogen is our only wide scale probe of this important era. Simulations of cosmic evolution predict a signal with angular scale of arc minutes and amplitude of 10 mK. I will report on our development of PAPER to detect the 3D power spectrum of the 21cm emission fluctuations in the redshift range 7-11. PAPER currently consists of dipole antennas spread across a field of 300m. Signals are combined in a digital correlator of novel design developed by the CASPER/RAL/KAT collaboration. Analysis--from calibration through to power spectrum estimation--is performed in a new software package, AIPY, developed by Aaron Parsons. Our first results from an exploratory PAPER deployed in Western Australia (WA) in 2007 July and an engineering PAPER deployed in Green Bank, WV will be described. A major deployment in WA is scheduled for 2009 August, and a roadmap into the decade ahead is being assembled for the A2010 committees.

Apr. 7, Tuesday 1:10 pm
Beth Reid, ICE, Bellaterra, Spain
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Applying the Halo Model to Large Scale Structure Measurements of the Luminous Red Galaxies: Results from SDSS DR7"
Cosmological constraints derived from large scale structure measurements are limited by our understanding of the relation between the underlying linear power spectrum and the observed galaxy distribution. I will focus on the SDSS Luminous Red Galaxy sample and show that using Finger-of-God features to reconstruct the underlying halo density field can substantially reduce the nonlinearity in the resulting power spectrum. Careful calibration of this technique with mock catalogs allows us to extend our cosmological parameter analysis for the SDSS LRG DR7 sample into the quasi-linear regime, k <= 0.2 h/Mpc, increasing the available number of modes by a factor of ~8 compared with previous analyses. We present cosmological constraints from the SDSS LRG DR7 power spectrum shape alone and in combination with WMAP5 and the Union Supernovae Sample.
Apr. 13, Monday 12:10 pm (TAC seminar)
Daisuke Nagai, Yale
544 Campbell Hall
"Thermodynamics of Galaxy Clusters and Beyond"
Clusters of galaxies are unique probes of cosmology and astrophysics, promising to provide new insights into both the nature of dark energy and dark matter and the physics of galaxy formation. One of the key challenge facing this approach lies in our understanding of cluster physics and their impact on cluster structure and evolution. In this talk, I will review recent development of theoretical and computational modeling of galaxy cluster formation, with focus on thermodynamics of intracluster plasma. I will show that modern numerical simulations including gas cooling and star formation reproduce thermodynamic properties of the intracluster medium (ICM) and observable-mass relations with an accuracy of ~10%. I will show that non-thermal processes (e.g., turbulence, cosmic-rays, and ICM plasma physics) are likely important for the remaining systematic uncertainty in the cluster mass estimate.
Apr. 14, Tuesday 1:10 pm
no talk, see Monday
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
tbd
Apr. 16, Thursday 4:00 pm (RPM)
Nissim Kanekar , NRAO
LBL 50A-5132
" Do the Fundamental Constants change with time ?"
Astrophysical studies of redshifted spectral lines provide a powerful probe of putative changes in low-energy fundamental constants across a large lookback time. After reviewing the current state of the field, I will describe a new radio technique, using ``conjugate'' satellite OH18cm lines, to measure changes in the fine structure constant \alpha, the proton-electron mass ratio \mu and the proton gyromagnetic ratio g_p, which is far less susceptible to systematic effects than other methods. I will then summarize our recent results from radio studies of fundamental constant evolution, based on three techniques: (1)~``conjugate'' satellite OH 18cm lines, (2) redshift comparisons between OH18cm and HI21cm lines, and (3)redshift comparisons between HI21cm and ultraviolet CI lines. Finally, I will discuss the improvements that are likely to be possible in such studies with the advent of new telescopes such as the EVLA and ALMA over the next decade.

Apr. 20, Monday 4:30 pm (Physics Colloquium)
Steven Kahn, Stanford
1 LeConte Hall
"The Large Synoptic Survey Telescope"
The Large Synoptic Survey Telescope (LSST) is a large-aperture, wide-field, ground-based optical telescope designed to provide a sensitive survey of the entire visible sky every few nights. The resulting database will enable a vast array of diverse scientific investigations ranging from studies of small moving objects in the solar system to the derivation of precise constraints on the structure and evolution of the universe as a whole. The development of LSST also involves a number of interesting technical challenges associated with its novel optical design, the requirement for an extremely large digital camera sensitive to the entire visible band of the spectrum, and the enormous data volume that this system will produce. In this talk, I will review the scientific motivations for this exciting project and some of the details of the technical design.
Apr. 21, Tuesday 1:10 pm
Tzu-Ching Chang , CITA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"21cm Cosmology"
Hydrogen is the most abundant element in the Universe, and in its neutral phase the 21cm hyperfine transition radiation has emerged to be a powerful tool in cosmology. I will describe our on-going effort to probe the Cosmic Reionization era with the 21cm line at z~9; our experiment at GMRT, India, aims to measure the 21cm power spectrum from Reionization. Furthermore, at redshifts around unity, we propose to measure the Baryon Acoustic Oscillation features using "Intensity Mapping" of the 21cm line, in order to efficiently probe the properties of dark energy to high precision. A first attempt to measure the hydrogen content at z~1 by cross-correlating HI data with the DEEP2 optical survey shows promising results.
Apr. 28, Tuesday 1:10 pm
Olivier Dore, CITA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Probing primordial non-gaussianity and testing gravity with large scale structure surveys"
The questions facing cosmologists are salient : inflation, dark energy and dark matter. However, the next generation of large scale structure surveys will allow us to address them in original ways. I will illustrate this with two examples which go beyond the obvious cosmological probes. The first one demonstrates how to constrain with unmatched sensitivity the primordial non-gaussianity using large scale galaxy clustering measurements. The second presents a new test of gravity on large scales using jointly weak-gravitational and galaxy surveys.
March 2009:
Mar. 2, Monday 2:00 pm (short informal talk)
Cecile Faure, Ecole Polytechnique Federale de Lausanne
LBL 50-5026 (INPA Common Room)
"On the correlation between strong lenses and the large scale environment"
Recently, hundreds of new strong galaxy-galaxy lenses have been discovered in large observational campaigns such as SLACS, COSMOS, and SL2S. After explaining why it is important to study strong lenses in the framework of their environment, I will report on the study of the spatial correlation of the COSMOS strong lens sample with the large scale strcutures traced by the X-ray clusters and by the weak-shear mass map. The observational results are compared with result from ray-tracing through the Milenniunm simulation.
Mar. 3, Tuesday 1:10 pm
Chris Hirata, CalTech
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Recent Developments in Cosmological Recombination"
The main theoretical uncertainty in the prediction of the primary CMB anisotropies is our ability to compute the ionization history (and hence the Thomson opacity) of the baryons during the first million years of the Universe. I will first review the basic physical processes that control the recombination of the primordial plasma, and then describe ongoing efforts to reduce the theoretical uncertainties to a level negligible for the Planck mission. I will discuss in detail 3 specific examples of processes that have been considered recently: helium-hydrogen interactions; two-photon decays and absorptions; and Lyman-alpha diffusion.
Mar. 5, Thursday 4:00 pm (RPM)
Cristiano Galbiati, Princeton
LBL 50A-5132
"MAX"
Evidence for the existence of dark matter is now compelling, but its nature remains a fundamental mystery. Particularly intriguing is the possibility that dark matter is made of Weakly Interacting Massive Particles (WIMPs). WIMPs may be detectable by their collisions with nuclei on Earth, but the low expected rate of such collisions and low energy of the recoil nuclei requires massive detectors with extremely low background rates, located in a deep underground laboratory. The development of a Deep Underground Science and Engineering Laboratory (DUSEL) will enable the deployment of WIMP detectors several orders of magnitude more sensitive than those operating today. I will discuss plans to search for WIMPs with twin xenon and depleted argon detectors at DUSEL.
Mar. 6, Friday 12:00 Noon
Norm Murray, Berkeley and CITA
LBL 50-5026 (INPA Common Room)
"On the maximum density of baryons on parsec and larger scales"
I will show that observations of stellar systems with masses ranging from 10,000 to 10^{12} solar masses have a maximum density. The upper envelope of the density at the half light radius scales as the inverse mass to the four fifths power. The density at a fixed physical radius, say ten parsecs, is also described by an upper envelope; the density at ten parsecs less than 10^{-17} g/cm^3, or 10^5 solar masses/pc^3. I will discuss possible explanations for this maximum density.
Mar. 9, Monday 12:10 pm (TAC seminar)
Andy Howell, UCSB/Las Cumbres
544 Campbell Hall
"Dark Energy, supernova evolution, dimming metals, and super-Chandra explosions: Latest results from the SNLS"
I show the latest Dark Energy constraints from 3rd year results of the Supernova Legacy Survey (SNLS), using ~250 SNLS SNe Ia at 0.1<1.0. Particular attention will be paid to systematic errors, especially the color/dust correction and the expectation for and evidence of a drift in the mean properties of SNe Ia with redshift. Many of these systematic errors are related to our ignorance of the SN Ia progenitor system -- I will summarize current knowledge, including SNLS measurements of changes in SN Ia properties with environment, rate measurements as a function of redshift, determinations of the delay time distribution between star formation and supernovae, and attempts to understand a possible super-Chandra explosion. Finally, I'll discuss the role of progenitor metallicity in determining SN Ia nickel yield and luminosity.
Mar. 10, Tuesday 1:10 pm
Salman Habib, LANL
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Percolation and the Large Scale Structure of the Universe"
The large-scale structure of the Universe, as traced by the distribution of galaxies, is now being revealed by large-volume cosmological surveys. The structure is characterized by galaxies distributed along filaments, the filaments connecting in turn to form a percolating network. In addition to conventional statistical measures such as two-point functions and power spectra, percolation theory can provide a useful set of global quantitative measures of cosmological structure. In this talk, as a first introductory example, I will discuss the application of percolation to statistics of cosmic voids. I will then discuss how a combination of percolation-based analyses and N-body simulations of the gravitational instability can characterize and provide insights into the formation of the cosmic network; how much of it originates in the properties of the initial density field ("nature") and how the contrast is then amplified by the nonlinear evolution of the Universe ("nurture").
Mar. 12, Thursday 4:00 pm (RPM)
Katrin Heitmann, LANL
LBL 50A-5132
"The Coyote Universe: Precision simulations of the large scale structure of the Universe"
Future cosmological observations targeted at investigations of dark energy pose stringent requirements on the accuracy of theoretical predictions for the clustering of matter. Currently, N-body simulations comprise the only viable approach to this problem. In this talk I will introduce the "Coyote Universe", a simulation suite of almost 1000 simulations, carried out to obtain high-precision predictions for large scale structure probes of cosmology. In order to obtain sub-percent accurate predictions for different cosmological models, two major challenges have to be overcome: (i) showing that the nonlinear regime of structure formation can be predicted at the targeted scales at the required accuracy level, (ii) building a prediction scheme for statistical quantities of interest such as the matter power spectrum over a range of cosmologies at matching precision but from a restricted set of costly simulations. This talk describes our recent work overcoming these challenges.
Mar. 13, Friday 12:00 noon (INPA talk)
Nick Ross, Penn State
LBL 50-5026 (INPA Common Room)
"The Clustering and Evolution of Quasars over the last 10 billion years"
I will present results from the SDSS DR5 Spectroscopic Quasar survey, examining the clustering properties of quasars via the 2-point correlation function. The evolution of quasar host haloes is discussed and put in context with other recent observational measurements (e.g. from the 2SLAQ and AGES surveys) and comparisons to theoretical models are made, including potential challenges to the "AGN Feedback" model. We then look ahead to the high redshift part of the Baryon Oscillation Spectroscopic Survey (BOSS) which will use the existing SDSS telescope with upgraded spectrographs to obtain 160,000 and z=2.2-3.5 quasar spectra.
Mar. 17, Tuesday 1:10 pm
Casey Papovich, Texas A & M
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Witnessing the Formation of Galaxies at High Redshift"
Studies of cosmologically distant galaxies with space-based and ground-based astronomical observatories have improved greatly our understanding of galaxy evolution. I will discuss recent results in understanding the formation of galaxies derived primarily from the Spitzer Space Telescope, which measures the infrared emission from obscured star formation and AGN in these galaxies. Combing the Spitzer and other multiwavelength data, we now have interesting constraints on the rates of the assembly of massive galaxies at high redshifts. I will discuss ongoing surveys to study massive galaxy assembly within high-density, large-scale structures at high redshift. And, I will describe a program to study gravitationally lensed distant galaxies, which provides a very detailed view of galaxy formation. I will summarize the open questions and challenges that remain in observational studies of galaxy evolution.
Mar. 18, Wednesday 12:10 pm (Wednesday Theory lunch)
Jun Zhang, UCB
501 Campbell Hall
"A Robust Way of Measuring the Cosmic Shear in Weak Lensing"
I will introduce a simple and efficient way of measuring the cosmic shear from galaxy shapes in weak lensing. The method is mathematically simple, well defined regardless of the morphologies of the galaxy and the point spread function. It even allows us to probe weak lensing effects on galaxy substructures, thereby improving the signal-to-noise ratio quite significantly. It also enables us to remove the systematic errors due to the photon noise and the pixelation effect in simple ways.
Mar. 19, Thursday 4:00 pm (RPM)
Seth Diegel, SLAC
LBL 50A-5132
"Early Results from the Fermi Large Area Telescope”"
The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope mission began routine science operations in early August 2008 and has already detected several times more celestial high-energy gamma rays (20 MeV to >300 GeV) than all current and past instruments in this energy range combined. In addition, the very large acceptance of the LAT and the unique scanning mode of observation provide complete sky coverage ~8 times per day, an important capability for observing the dynamic high-energy sky. The status and early results from the LAT, including the LAT Bright Source List and diffuse gamma-ray mission, will be summarized.
Mar. 30, Monday 4:30 pm (Physics Colloquium)
Chris Stubbs, Harvard
1 LeConte Hall
"Confronting the Dark Energy Crisis in Fundamental Physics"
The discovery of the accelerating expansion of the Universe has precipitated a crisis in fundamental physics. Dark Energy, which drives the apparent gravitational repulsion between regions of empty space, poses a major challenge to our understanding of the interface between gravity and quantum mechanics. I will describe projects, both under way and in the planning stages, that are designed to improve our understanding of the Dark Energy problem.
Mar. 31, Tuesday 1:10 pm
Bhuvnesh Jain, Penn.
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Testing Gravity with Gravitational Lensing and Dynamics"
Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the universe. In this talk, I will describe tests of gravity from kpc-Gpc scales using gravitational lensing and the dynamics of galaxies and clusters.
February 2009:
Feb. 2, Monday 12:10 pm (TAC seminar)
Peng Oh, UCSB
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Helium Reionization: A Testbed for Ideas about Reionization"
The study of hydrogen reionization is an extremely active research area today. Progress is hindered by paucity of observational constraints, as well as the many unknowns in theoretical models. By comparison, much more is known about helium reionization: the abundance and clustering of likely sources (quasars), as well as the state of the z~3 IGM (from Ly-alpha forest observations). By all accounts, Helium reionization should be a solved problem. Yet, to date, there are strong disagreements about when and how it took place, and puzzling observations which lack convincing interpretation. I survey some of these, and focus on the thermal effects of Helium reionization, and possible signatures of Helium reionization in the hydrogen Ly-alpha forest.
Feb. 3, Tuesday 1:10 pm
Elena Pierpaoli, USC
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"What can the CMB still tell us, after all these years?"
The study of the Cosmic Microwave Background radiation has revolutionized our understanding of the Universe in the past fifteen years. In two months the Planck satellite will be launched and will deliver exquisite data, allowing to pin down cosmological parameters wih an increased precision. The planning for future CMB missions is underway. I will review what we expect to learn from Planck on reionization and inflationary parameters. I will then discuss the prospects for future missions, also in the light of foreground contributions to the CMB frequencies.
Feb. 5, Thursday 4:00 pm (RPM)
Yasunori Nomura, UCB/LBNL
LBL 50A-5132
"Dark Matter: Current and Future"
The physics of dark matter is reviewed. This is a theory background/introduction talk to the upcoming discussion of dark matter experiments, and the presentation will be at a basic level.
Feb. 5, Thursday 4:10 pm (Astronomy Colloquium)
Martha Haynes, Cornell
1 LeConte Hall
HII Cosmology in the Local Universe with ALFALFA
The Arecibo Legacy Fast ALFA (ALFALFA) survey is an on-going second generation blind extragalactic HI survey exploiting Arecibo's superior sensitivity, angular resolution and digital technology to conduct a census of the local HI universe over a cosmologically significant volume. When complete in 2-3 years, ALFALFA will detect more than 25,000 extragalactic HI line sources out to z~0.06, and its catalog will be especially useful in synergy with wide area surveys conducted at other wavelengths. ALFALFA is detecting HI masses as low as 10**6 solar masses and as high as 10**10.8 solar masses with positional accuracies typically better than 20 arcsec, allowing immediate identification of the most probable optical counterpart to each HI detection. In the region of the Virgo cluster of galaxies, a number of optically dark HI sources have been found. These all lie in the outskirts of the cluster and could be a mixture of "harassment" debris and ram-pressure stripping events. First ALFALFA results already indicate, in agreement with the suggestions of previous, more limited studies, that there is not a cosmologically significant population of optically dark but HI rich galaxies. However, the majority of ALFALFA detections are too optically faint or of low surface brightness to have been included in previous targeted HI surveys. ALFALFA promises a wealthy dataset for the exploration of many issues in near-field cosmology and galaxy evolution studies, setting the stage for future extension of these investigations to higher redshifts with the Square Kilometer Array.
Feb. 9, Monday 2:30 pm
Mark Wise, Caltech
402 Old LeConte
"Translation Invariance and the Anisotropy of the Microwave Background"
Feb. 10, Tuesday 1:10 pm
Chris Carilli,NRAO
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Massive galaxy formation in the early Universe"
I will present recent radio and (sub)mm observations of the atomic and molecular gas, dust, and star formation, in the host galaxies of z ~ 6 quasars. These are the only direct observations of the host galaxies of these Gunn-Peterson quasars. The host galaxies are under-going extreme starbursts, with star formation rates > 1000 Mo/year, and molecular gas masses in excess of 1e10 Mo. Through gas dynamics, we can estimate the ratio of the bulge mass to black hole mass. These observations imply that we are witnessing the co-eval formation of massive elliptical galaxies, and super-massive black holes, within 1 Gyr of the Big Bang. I will present details on gas excitation, dust temperature, and the FIR-L'CO relation (the 'integrated Kennicutt-Schmidt law'). Current telescopes are limited to studying the most extreme objects at these redshifts. I will discuss how future telescopes, such as ALMA, the EVLA, and eventually, an SKA, will reveal the cool gas, dust, and star formation, in normal galaxies at extreme redshifts (LAEs and LBGs).
Feb. 10, Tuesday 4:00 pm (RPM)
Tom Shutt, Case Western LBL 50B-4205**LOCATION CHANGE**
"LUX, LZ20 and the Race to Detect WIMP Dark Matter"
Overwhelming cosmological and astrophysical evidence suggests that the dominant mass in the universe is in the form of as-yet- unidentified dark matter. The most favored candidate for dark matter is weakly interacting particles (WIMPs), which are also a generic prediction in supersymmetry. WIMPs in our galaxy can be measured by their interactions in detectors operated deep underground with backgrounds from radioactive and cosmic-rays suppressed by some 10 orders of magnitude from ambient levels. Recent advances in detectors based on liquified noble elements promise a radical increase in the sensitivity of these experiments, and will allow a nearly complete test of supersymmetric dark matter in the next decade. Such efforts are complementary to the LHC. The LUX experiment is constructing a 300 kg liquid Xe-based detector that will be operated in site of Ray Davis' original solar neutrino experiment in the Homestake mine in South Dakota. I will discuss LUX, and also LZ20, a 20 ton experiment proposed as part of the integrated suite of experiments of DUSEL. LZ20 would be an ultimate direct dark matter detection experiment, closing the available WIMP search window on Earth that is finally limited by the signal from coherent scattering of astrophysical neutrinos.
Feb. 12, Thursday 4:00 pm (RPM)
Gabriella Sciolla, MIT LBL 50A-5132
"DM-TPC: A Novel Apparatus for Directional Dark Matter Detection"
Directional detection is key to provide unambiguous observation of dark matter even in the presence of insidious backgrounds. The DM-TPC collaboration is developing a TPC with optical readout with the goal of detecting the sense and direction of the elastic recoils generated by Dark Matter interactions. The detector, filled with CF_4 gas at low pressure, is equipped with a mesh-based amplification region that allows for 2D imaging of the recoils in a CCD camera. The third coordinate of the recoil is provided by PMTs. The sense of the direction is determined by measuring the energy loss along the recoil track. The performance of this detector has been studied using alpha particles, low-energy neutrons, and x-rays. Results from a first prototype clearly demonstrated the suitability of this approach to measure directionality by observing the "head-tail" effect for low- energy nuclear recoils. Two 10-liter prototypes of the DMTPC detector have recently been built, and are ready to be moved to an underground laboratory for a one-year run in 2009. A larger (1m3) detector is also being designed. A one-year underground run with such detector will allow us to improve the current sensitivity on spin-dependent interaction on protons by about a factor 50.
Feb. 17, Tuesday 1:10 pm
Changbom Park,Korea Institute for Advanced Study
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
Large-Scale Structure of the Universe as a Cosmic Ruler
Since the shape of the linear-regime power spectrum should be maintained in the comoving space as time passes, one can draw information on absolute scales from it. A comparison of the shape of the linear-regime power spectrum at two different epochs, knowing they should be the same, can tell us about how the universe has expanded between the epoches. Therefore, just like the baryon acoustic oscillations that appear as tiny wiggles in the power spectrum, the whole shape of power spectrum can be used for extracting the scale information and to measure cosmological parameters like the equation of state of dark energy.
In order to reduce various non-linear effects in the shape of the power spectrum we propose to use the large-scale structure of the universe as a cosmic ruler and its sponge topology as a measure of the shape of the power spectrum.
Feb. 19, Thursday 4:00 pm (RPM)
Jeff Peterson, CMU
LBL 50A-5132
"21 cm intensity mapping with a Transit Cylinder Radio Telescope"
By making all-sky observations of 21-cm flux at redshifts near one, the large scale structure of the Universe can be mapped in three dimensions. This can be accomplished by studying specific intensity with resolution ~ 10 Mpc, rather than via the usual galaxy redshift survey. This new technique is called intensity mapping. A new type of radio telescope based on fixed cylinders has been proposed for these observations, and I will report the progress of the testing of a prototype cylinder telescope built in Pittsburgh. The primary goal of the program is to detail the expansion history, in order to constrain dark energy models. To accomplish this the telescope will have mapping speed about 1000 times faster than any current radio telescope. This means the telescope will also provide a rich set of synoptic data.
Feb. 20, Friday 12:00 Noon
Josh Bloom, Berkeley
LBL 50-5026 (INPA Common Room)
"SASIR: the Synoptic All-Sky Inrared Survey "
Feb. 24, Tuesday 1:10 pm
Eduardo Rozo, Ohio State
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Self-Calibrated Cosmological Constraints from the SDSS Cluster Abundances"
I will present cosmological constraints from a self-calibrating cosmological analysis of cluster abundances in the Sloan Digital Sky Survey (SDSS), and interpret our results within a broad cosmological framework. I will also compare our results to those X-ray cluster abundance studies, and demonstrate that they are in excellent agreement and are of comparable accuracy. This non-trivial agreement demonstrate cluster abundances are a robust tool for precision cosmology.
Feb. 24, Tuesday 4:00 pm (RPM)
Wick Haxton, U. Washington
LBL 50A-5132
"Science Motivations for DUSEL"
A summary will be presented of the physics case for DUSEL, based in part on the recent Theory White Paper organized by the Ohio State group and on various versions of the "Science Book" drafted over the past six years. The focus will be on neutrinos -- particularly solar and supernova -- and on nuclear astrophysics.
Feb. 26, Thursday 4:10 pm (Astronomy Colloquium)
Eichiro Komatsu, Texas
1 LeConte Hall
"Testing Physics of the Early Universe Observationally: Are Primordial Fluctuations Gaussian or Non-Gaussian?"
How can we test competing theories about the origin and evolution of the universe? The most direct observational probes are the statistical properties of the primordial density fluctuations. Current evidence strongly suggests that they were generated as quantum fluctuations and that their probability distribution is very close to gaussian, consistent thus far with the simplest class of cosmic inflation models but also with alternatives that predict larger deviations from gaussianity. Improving constraints on non-gaussianity is now recognized as one of the most powerful and fundamental observational tools for understanding the physics of the early universe. In this talk, I will discuss how to search for primordial non-gaussianities in observational data, the current state of affairs and future prospects.
Feb. 26, Thursday 4:00 pm (RPM)
Bernard Sadoulet, Berkeley
LBL 50B-4205
"The Germanium Observatory for Dark Matter at DUSEL (GEODM)"
The search for Weakly Interactive Massive Particles (WIMPs) which may constitute the Dark Matter in the Universe is clearly a high priority and is one of the justifications for the Deep Underground Science and Engineering Laboratory (DUSEL) in the US. The simultaneous athermal phonon and ionization measurement in germanium detectors at low temperature is are the only demonstrated technology which has negligible background in the search for WIMPs. The challenge is to extrapolate this approach to the ton scale within the next ten years with zero background and at reasonable cost and construction time. I will describe the approach we propose in our recent S4 proposal to NSF and an accompanying proposal to DOE and how this articulates with the pre-DUSEL program. I will emphasize the role that LBNL could play.
Feb. 27, Friday 12:00 noon (INPA talk)
Rollin Thomas, LBNL
LBL 50-5026 (INPA Common Room)
"Nearby Supernova Factory Showroom"
The Nearby Supernova Factory has successfully completed a 4-year program of end-to-end discovery and detailed spectrophotometric follow-up of supernovae at z < 0.1. Over 1000 supernovae of all types were discovered, 600 of which were spectroscopically confirmed, and almost 400 of these Type Ia. Spectrophotometric time series were obtained for about 160 Type Ia supernovae suitable for use as cosmological distance indicators, detailed studies of supernova systematics, and improving our understanding of the physics of these events. I will summarize the progress of our survey over its history, present light-curves and our current low-redshift Hubble diagram, and highlight particularly unique and interesting analyses we have undertaken with this rich dataset. In particular, I will discuss a new single-epoch spectroscopic luminosity indicator competitive with (or even more effective than) existing light-curve/color corrections.
January 2009:
Jan. 6, Tuesday 3:40 pm (string seminar)
Alan Guth, MIT
402 Old LeConte
"Spacetime probabilities and the scale-factor cutoff measure"
Jan. 13, Tuesday 1:10 pm CANCELLED due to VISA problem!
Qi Guo, MPA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
tbd
Jan. 20, Tuesday 1:10 pm
Brice Menard, CITA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Measuring the galaxy-mass and galaxy-dust correlations through magnification and reddening"
I will present a simultaneous detection of gravitational magnification and dust reddening effects due to galactic halos and large-scale structure. The measurement is based on correlating the brightness of 100,000 quasars at z>1 with the position of 20 million foreground galaxies derived from the SDSS. (i) From magnification measurements we constrain the galaxy-mass correlation up to 20 Mpc scales and compare the results with estimates from gravitational shear. (ii) From reddening measurements we constrain the galaxy-dust correlation from 20 kpc to several Mpc, providing the first constraints on the amount of dust in galactic halos and beyond. I will present the spatial distribution and wavelength dependence of this diffuse dust component. I will then estimate of the opacity of the Universe, the cosmic density of dust and the implications for supernova experiments.
Jan. 22, Thursday 4:10 pm (Astronomy Colloquium)
Andy Lawrence, Edinburgh
1 LeConte Hall
"The Ukirt Infrared Deep Sky Survey (UKIDSS)
UKIDSS is a suite of IR surveys being carried out using the UKIRT Wide Field Camera, starting in 2005 and expected to complete around 2011. Three wide area surveys cover the Galactic Plane and the high latitude sky to K=18.5, totalling seven thousand square degrees, with smaller deeper surveys reaching to K=23. These surveys are making an impact on studies of high-z quasars, very cool brown dwarfs, galaxy clustering, high redshift galaxy formation, and many other areas. Data are immediately public to European astronomers and world-public eighteen months later. Data are made available through a queryable database system similar to that used by SDSS, but are also now available through VO tools in conjunction with many other resources. I will summarise the status of UKIDSS, show some science highlights, and give a live demo of data access and VO tools.
Jan. 27, Tuesday 1:10 pm
Kendrick Smith, Cambridge
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"The cosmic microwave background beyond the power spectrum"
The main tool for extracting cosmological information from the CMB to date has been the power spectrum or two-point function. In the approximation that the CMB is a Gaussian field, the power spectrum contains all the information, but weak non-Gaussian effects from secondary anisotropies or from non-standard inflationary models can be extracted using higher-point statistics. We present higher-point statistics for extracting the signals due to CMB lensing, patchy reionization, and primordial non-Gaussianity from inflation, including results from the first optimal analysis of primordial non-Gaussianity in WMAP.
Jan. 29, Thursday 4:10 pm (Astronomy Colloquium)
Avishai Dekel, Tel Aviv
1 LeConte Hall
"The Main Mode of Galaxy Formation: Cold Streams, Clumpy Disks and Compact Spheroids"
Many of the massive galaxies in the young universe formed stars at surprising intensities. While this was commonly attributed to violent mergers, most of these galaxies are incompatible with mergers, showing clumpy, extended rotating disks. In parallel, a large fraction of the z~2 galaxies are compact spheroids with suppressed star-formation rates (SFR), too abundant to be explained by major mergers. Hydro cosmological simulations reveal that most of the star formers are Stream-Fed Galaxies, growing via steady, narrow, cold gas streams that penetrate through the shock-heated media of massive dark-matter halos, and rapidly turn into stars. On average, one third of the stream mass is in gas clumps leading to mergers and the rest is in smoother flows. A simple theoretical analysis reveals that the evolution of high-redshift disks is governed by the interplay between fueling by smooth and clumpy streams and stabilization by a spheroid of dark matter and stars, leading to a bimodality in galaxy type by z~3. Disks of giant clumps and high SFR form when the streams are relatively smooth. The streams maintain a dense disk that undergoes gravitational fragmentation into giant clumps, whose mutual encounters self-regulate the instability with a high velocity dispersion. Encounters and dynamical friction induce rapid inward clump migration while the disk expands in response. The streams replenish the draining disk and extend the duration of the clumpy phase to several Gyr in a steady state. The clumps form stars at the accretion rate and each turns into stars in several dynamical times. The migrating clumps coalesce dissipatively into a compact bulge. Passive spheroid-dominated galaxies form when the incoming streams are more clumpy. These external clumps stir up turbulence in the disk and grow a dominant bulge; together they stabilize the disk and suppress in-situ clump and star formation. This scenario explains the bimodality observed at z~2, of clumpy star-forming extended disks alongside with compact spheroids of suppressed SFR. High-resolution cosmological simulations reveal clumpy disks consistent with this analysis.
December 2008:
Dec. 1, Monday 2:30 pm
Leonardo Senatore, Harvard
402 Old LeConte
"The Volume of the Universe after INflation and de Sitter Entropy"
Dec. 2, Tuesday 1:10 pm
Fritz Stabenau , Penn.
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Photo-z's in the optical and the submillimeter"
Recent measurements have shown that the expansion of the universe is accelerating. In order to extrapolate GR to fit the properties of the universe on horizon scales, a strange form of energy density (``dark energy'') is required. An alternative to dark energy is a modification of GR that accounts for accelerating expansion. In this talk, I will discuss my work on predicting large-scale structure formation in an alternative gravity model by N-body simulation. A related problem that I have worked on is efficiently obtaining accurate redshifts for galaxies using photometric redshifts with surface brightness priors. Finally I will talk briefly about my ongoing work on analyzing data from the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) experiment.
Dec. 4, Thursday 4:10 pm (Astronomy Colloquium)
Asantha Cooray, Irvine
2 LeConte Hall
"Missing IR Background: Spitzer and CIBER"
The DIRBE extragalactic background light measurements at near-IR wavelengths is factor of a few or more higher than the integrated background produced by known star and galaxy counts in existing surveys. The missing light has been ascribed to reionizing sources and claims have been made for a large surface density of high redshift sources based on clustering of fluctuations in deep Spitzer images. I will show results from our studies with NICMOS and IRAC that question these claims and show that the missing light cannot be associated with the first-light galaxies. This still requires an unknown source to explain most of DIRBE light. To address this, we discuss an attempt to remeasure the IR background light with a sounding rocket experiment, CIBER. In the remaining time, I will briefly discuss plans for cosmological studies with Herschel in the wide-field Herschel-ATLAS survey.
Dec. 5, Friday 10:10 am
Wayne Hu, Chicago
402 Old LeConte
"Cosmic Acceleration from Modified Gravity: A Worked Example"
Dec. 9, Tuesday 1:10 pm
Mark Vogelsberger, MPA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Hunting Dark Matter-Insights from N-body simulations"
The observational evidence for dark matter is very striking today. However, the elusive dark matter particles were not yet detected. Detector signals are strongly influenced by the dark matter phase-space distribution. In my talk I will present recent results on the local dark matter phase-space structure based on ultra-high resolution N-body simulations. I will show how the spatial and velocity distribution look like and how they influence direct detection experiments. In the second part of my talk I will discuss the fine-grained phase-space structure. I will present a new technique that allows to resolve the dark matter small-scale structure for the first time. As an application I will briefly describe how dark matter caustics can be analyzed with this method.
Dec. 10, Wednesday 4:00 pm
Genevieve Graves, Santa Cruz
LBL 50A-5132
"Dissecting the Red Sequence: Star Formation Histories and Structure of Early Type Galaxies"
I use 16,000 galaxy spectra from the Sloan Digital Sky Survey to probe the varying stellar populations of early type galaxies throughout the structural space described by the Fundamental Plane. Not only do early type galaxies span a 2-dimensional family in the Fundamental Plane, they also span a 2-dimensional family in star formation histories. In addition to known variations with galaxy mass, I present evidence that stellar populations in these galaxies are intimately linked with their central dark matter fraction, revealing a connection between star formation history and structural evolution of the galaxy. I discuss these results in the context of different models for galaxy evolution in a hierarchical universe.
November 2008:
Nov. 3, Monday 4:30 pm (Physics Colloquium)
Nima Arkani-Hamed ,IAS
1 LeConte
"Dark Forces for Dark Matter"
I will describe a new picture of Dark Matter that explains the recent proliferation of unexpected observations in high-energy astrophysics. I will then discuss an array of predictions for direct and indirect Dark Matter detection experiments, as well as the smoking gun signals for this theory at the Large Hadron Collider.
Nov. 4, Tuesday 1:10 pm
Sudeep Das , Princeton
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"CMB Lensing: A New Tool for Astrophysics and Cosmology"
Large scale structure in the universe deflects cosmic microwave background (CMB) photons by roughly 3 arcminutes. This deflection field reflects the history of cosmological expansion and growth of structure. With high resolution ground based CMB experiments like the South Pole Telescope and the Atacama Cosmology Telescope already underway, and the space based Planck satellite nearing its launch, time is ripe for perfecting a new set of tools and ideas to reap the scientific benefits of this exciting effect. I will describe high resolution simulations, new analysis techniques and theoretical expectations for an array of possible projects involving CMB lensing and large scale structure surveys which will shed new light on dark energy, dark matter and galaxy formation.
Nov. 5, Wednesday 12:30 pm
Valeria Pettorino, Heidelberg
LBL 50-5026 (INPA Common Room)
"Clustering in interacting dark energy cosmologies"
I will illustrate the case of interacting dark Energy, that is to say cosmologies in which the dark energy scalar field interacts with other things in the universe (gravity, cold dark matter or neutrinos). After briefly presenting the status of our work for the first two classes of models, regarding both linear perturbations and Nbody simulations, I will in particular focus on the appealing case of 'growing neutrinos': in these models, neutrinos with a mass increasing with time might be driven to cluster at very large scales, due to a new interaction stronger than gravity and mediated by the dark energy scalar field.
Nov. 6, Thursday 4:00 pm
Rob Caldwell, Dartmouth
LBL 50A-5132
"Dark Energy Reference Frames and Forces"
The challege to understand the physics of cosmic acceleration has raised interest in alternatives to the concordance, cosmological constant scenario. Many of these models, while based on far less exotic physics, introduce special reference frames and forces. We show how current and forthcoming experiments can help distinguish among the possibilities.

Nov. 7, Friday 12:10 pm
Rik Williams, Leiden
544 Campbell Hall
"The growth of quiescent galaxies over the past 11 Gyr"
The buildup of stellar mass at z~2, the process(es) by which the star formation in these galaxies is quenched, and the evolution of the quenched galaxies into the present-day elliptical population are a few of the fundamental problems being tackled by observers and theorists alike. On the observational side, one primary obstacle has been small sample sizes: spectroscopic redshifts and star formation rate measurements at z=1-2 are difficult to obtain, especially for massive but relatively faint galaxies that are either dust-obscured or "red and dead." To overcome this, we combine photometric redshifts, a novel diagnostic employing two rest-frame colors, and deep public near-IR, optical, and Spitzer imaging to divide ~30000 K-selected galaxies into star-forming and quiescent subsamples (the analogs of nearby "red sequence" and "blue cloud" galaxies, respectively) over z=0.3-2.0. I will give an overview of the data and rest-frame color analysis, compare and contrast the basic properties of the quiescent and star-forming samples, and present initial results showcasing how such large, statistical surveys can be used to address the aformentioned problems in galaxy formation.
Nov. 7, Friday 3:00 pm (note special time!)
Peter Capak, IPAC
LBL 50-5026 (INPA Common Room)
"New Perspectives on Galaxy Evolution From the COSMOS Survey"
The 2 square degree COSMOS HST field has become one of the best for studying galaxy formation and evolution. At redshifts greater than 1 COSMOS probes a volume similar to the SDSS in the local universe with similar sensitivity and resolution. It has deep coverage from Chandra, XMM, Galex, Hubble, and Spitzer along with extensive ground based observations from the UV to the radio and over 30,000 spectra from VLT, Keck, and Magellan. This superb data allows for photometric redshifts accurate to dz/(1+z)=0.01 for both galaxies and AGN at i<24, allowing for large statistical studies of galaxy evolution. The majority of this data has been or will be released to the public in the next three months.
This talk will focus on new insights on galaxy formation and evolution from these data. This cosmologically significant volume provides strong constraints on the formation of massive galaxies. I will show several bright z~7 galaxy candidates selected as dropouts from deep infrared imaging, a gas rich major merger at z=4.547 forming stars at over 2000 solar masses per year, and the evolution of the UV luminosity function between 4
Nov. 11, Tuesday 1:10 pm
Tsz Yan Lam , Penn.
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Analytical collapse models and nonlinear probability distribution function"
Analytical methods describing the nonlinear evolution of the probability distribution function (PDF) of the smoothed dark matter density field will be discussed. I provide a simple approximation to the exact ellipsoidal collapse model which shows how the evolution can be thought of as a modification of the spherical evolution model as well as of the Zeldovich Approximation. I will discuss the results of applying the analytical PDF calculation to the local non-Gaussian model and the possibility to constrain non-Gaussianity by measuring the nonlinear dark matter PDF.
Nov. 14, Friday 4:00 pm (RPM)
Max Tegmark , MIT
LBL 50A-5132
"Probing energy, dark matter and inflation with 21 cm tomography"
I discuss outstanding puzzles in cosmology such as the nature of dark matter, dark energy and the early universe, and discuss recent developments as well as the prospects of dramatically better measurements from mapping neutral hydrogen in a large fraction of our Hubble volume.
Nov. 18, Tuesday 1:10 pm
Oliver Hahn, Zurich
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Galaxy Formation in the Filamentary Cosmic Web"
Galaxy redshift surveys have provided us with a detailed picture of the large-scale distribution of galaxies in the Universe: galaxies and mass are known to be embedded in a web-like spatial structure made up from dense clusters connected by massive filaments and otherwise near-empty void regions. Cosmological N-body simulations have shown that this cosmic web arises naturally by gravitational instability from tiny density perturbations seeded in the very early Universe. I will present a classification scheme for large-scale structure based on tidal stability, that allows to associate halos to clusters, filaments, sheets or voids. Applying this scheme to simulations of cosmic structure formation, I will discuss several key aspects of the environment dependence of halo formation and evolution in the context of the cosmic web: the influence of environment on the build-up of halo mass, and alignment correlations of halo spin and shape with the large-scale structure and its implications for cosmic shear measurements.
Nov. 20, Thursday 4:10 pm (Astronomy Colloquium)
Maxim Markevitch , CfA
2 LeConte Hall
"Hydrodynamics of galaxy clusters from Chandra and numeric simulations"
As a consequence of Chandra X-ray observations of galaxy clusters, they can no longer be thought of as spherically symmetric, isothermal beta-model gas clouds in hyrdostatic equilibrium. We have discovered bow shocks and "cold fronts" in merging clusters, as well as sloshing of cool, dense gas at the centers of clusters previously considered completely relaxed. I will show lots of striking X-ray images along with results from our attempts at reproducing the above phenomena in numeric simulations, and discuss what we can learn about cluster physics from these data.
Nov. 21, Friday 12:00 Noon
Douglas Scott, UBC
LBL 50-5026 (INPA Common Room)
"Crazy Things to do with the Cosmic Microwave Background"
Nov. 25, Tuesday 1:10 pm
Sanghamitra Deb, Drexel
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"What can we learn from Cluster Lensing?"
Clusters exhibit a range of different lensing effects. There are strong lensing effects close to the core where multiple images and highly distorted arcs are formed. Close to the edges there is the weak distortion of background galaxy ellipticities. Since all the effects are produced by the same lensing potential we should be able to combine all of them. These different lensing observables have a different signal to noise ratio. Thus to combine them we have developed a technique "Particle Based Lensing (PBL)". In this technique the smoothing scale can be varied spatially to accommodate the observables with different signal-to-noise ratio. We have applied this technique to several toy lens models to obtain excellent agreement with the input mass distribution. We have also done a mass reconstruction for the well known "Bullet Cluster" using PBL.
Nov. 26, Wednesday 12:10 pm, Wednesday Theory Lunch
Douglas Scott, UBC
501 Campbell Hall
"Results from the Balloon-borne Large Aperture Submillimeter Telescope"
October 2008:
Oct. 1, Wednesday 12:10 pm, Wednesday Theory Lunch
Smadar Naoz, Tel Aviv
501 Campbell Hall
"The first generation of galaxies and 21cm fluctuations"
The formation of the first generation of galaxies in the Universe has been studied for many years. We studied this epoch taking into account important physical ingredients. We show that these ingredients play a major role in the evolution of over-densities both in the linear and non-linear regime and on the formation and properties of the first luminous objects in the Universe. We give a detailed set of predictions for these objects, and in particular show that the first observable star was most likely to form only 30 million years after the big bang (at redshift 65), with the first Gamma ray burst exploding only a few million years later. Observations of the 21cm radiation from these epochs will help unfold the cosmic evolution of the first generation of galaxies. These observations are strongly affected by the UV radiation from stars at this era which couples the properties of the 21cm signal and the distribution of the first galaxies. Using an accurate analysis of this coupling process, including the ionized gas bubble around each galaxy, we predict a clear signature of this process. We show that such observable signatures can be used to detect and study the population of galaxies that formed as early as 200 Myr after the big bang.
Oct. 2, Thursday 4:10 pm (Astronomy Colloquium)
Bill Holzapfel, UCB
2 LeConte Hall
South Pole Telescope: A new probe of cluster cosmology
The South Pole Telescope (SPT) is a 10-meter diameter telescope, with a 960 element millimeter-wavelength bolometric receiver, which is nearing the end of its second season of observation the South Pole. The SPT has been optimized for observations of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters, which is the inverse Compton scattering of the Cosmic Microwave Background (CMB) by hot intra-cluster gas. With this instrument, we are surveying the southern sky to create a mass limited catalog of galaxy clusters out to the epoch of their formation which can be used to place new constraints on cosmological parameters such as the dark matter density and dark energy equation of state. This program of observations will also produce significant detections of the kinetic SZ effect and weak gravitational lensing of the CMB, a large multi-band millimeter-wavelength point source catalog, and images of the SZ effect in known galaxy clusters with unprecedented sensitivity. In this talk, I will discuss the science goals of the experiment, the design, construction, and deployment of the SPT, progress of the observations, and conclude by showing some preliminary results.
Oct. 7, Tuesday 1:10 pm
Francesco Shankar, MPA/OSU
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Constraining the evolution of Super-Massive Black Holes"
Supermassive black holes (SMBHs) seem to be ubiquitous at the center of all galaxies which have been observed with high enough sensitivity with HST. SMBH masses are tightly linked with the masses and velocity dispersions of their host galaxies. Also, SMBHs are considered to be the central engines of active galactic nuclei (AGN). It is however still unclear how SMBHs have grown and if they have co-evolved with their hosts. In my talk I will derive, in ways independent of specific models, constraints on how SMBHs must have evolved within their dark matter halos. I will describe the accretion history of SMBHs from z~6 to z~0 by interconnecting a variety of data sets, including the AGN luminosity function, their clustering properties, and Eddington ratio distributions. I'll show results obtained through a novel numerical code which evolves the SMBH mass function and clustering adopting broad distributions of Eddington ratios.

Oct. 9, Thursday 4:10 pm (Astronomy Colloquium)
Dan Marrone, Chicago
2 LeConte Hall
"Sunyaev-Zel'dovich Effect Science with the SZA and CARMA"
Observations of galaxy clusters through the Sunyaev-Zel'dovich effect have matured rapidly, proceeding in a period of a few years from samples of tens of objects to surveys designed to constrain dark energy with thousands of new cluster detections. Nevertheless, very little observational work has been done to understand the effects of astrophysics and the systematics of the SZ effect in clusters. We are presently using the Sunyaev-Zel'dovich Array, an interferometer optimized for cluster SZ observations, to characterize the SZ signal in known clusters with particular focus on the crucial SZ-mass relationship. Through the Local Cluster Substructure Survey (LoCuSS) we are able to study many tens of clusters via SZ and X-ray imaging, weak and strong gravitational lensing maps, and many other tracers. I will present a few results from the SZA and LoCuSS, including our first examination of the scaling between the SZ signal and gravitational lensing mass. Because gravitational lensing masses are derived without the assumption of hydrostatic equilibrium, as must be done to obtain cluster masses from SZ and X-ray data, this scaling provides an estimate of the non-thermal support in galaxy clusters. I will also discuss our ongoing observational program and the new capabilities enabled by the merging of the SZA and CARMA. The significant sensitivity increase that CARMA provides will allow us to make detailed images of cluster cores, where simulations have difficulty reproducing observational details and where the most important SZ systematics will likely reside.
Oct. 14, Tuesday 1:10 pm
Marilena LoVerde , Columbia
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Observations Through a Lumpy Universe"
Weak lensing of high redshift galaxies and quasars leads to a well know adjustment of galaxy/quasar source counts called magnification bias. I will discuss how magnification bias complicates high redshift measurements of the integrated Sachs-Wolfe effect, distorts the observed angular and 3D galaxy correlation functions, and alters measurements from the Lyman-alpha forest. Magnification bias can have a surprisingly large effect on these observables and if not accounted for, bias the inferred values of cosmological parameters. Finally, I will discuss how magnification can be a source of information rather than just a systematic.
Oct. 15, Wednesday 3:10 pm (special RAL seminar)
Ravi Subrahmanyan , Raman Research Institute
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Deep Surveys of the Radio Universe"
Oct. 16, Thursday 4:10 pm (Astronomy Colloquium)
Alison Coil, UCSD
2 LeConte Hall
"Clustering, Quenching, and Feedback: Galaxies and AGN at z=1"
Roughly half of the red elliptical galaxies observed today have formed since z=1. I will present galaxy clustering results from the DEEP2 Redshift Survey that strongly constrain the mechanism responsible for the quenching or cessation of star formation in these galaxies. I will show where this quenching is occurring on large scales and how it can not be due primarily to cluster-specific physics. I will also present results on the clustering of optically-bright quasars and X-ray selected AGN and show how AGN accretion correlates with the star formation activity in galaxies at z=1. I will also show new results on the prevalence of outflowing galactic winds at z=1 and discuss their role in quenching star formation. Finally, I will present a new wide-area prism survey that will allow further studies of galaxy evolution to z=1 with the largest faint galaxy survey to date.
Oct. 20, Monday 3:10 pm
Jonathan Pober, Berkeley
544 Campbell Hall
"Sunyaev-Zel'dovich Observations of Clusters with the Arcminute Microkelvin Imager"
The Arcminute Microkelvin Imager is an SZ survey telescope that has recently been commissioned in Cambridge. Its main goal is to carry out a blind, mass-limited survey of galaxy clusters in order to constrain their comoving number density as a function of mass and redshift. The telescope has been making pointed observations of known X-ray and optically-selected clusters in order to examine the cluster scaling relations, and blind cluster surveys commenced this summer. I shall describe the instrument and some pointed SZ observations and then outline the strategy and prospects for blind surveys.
Oct. 21, Tuesday 1:10 pm
Matt McQuinn, Harvard/CfA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"HeII Reionization and Its Effect on the IGM"
Observations of the intergalactic medium (IGM) suggest that quasars reionize the HeII at z ~ 3. HeII reionization heats the IGM by tens of thousands of Kelvin, and it affects the statistics of the HI and HeII Lyman-alpha forests. I will present a set of simulations of HeII being reionized by quasars. These simulations lead to a different picture for this process than in previous studies. If quasars have a mean spectral index of 1.5, I find that HeII reionization heats regions in the IGM by as much as 30,000 K above the temperature that is expected otherwise, with the volume-averaged temperature increasing by ~10,000 K and with large temperature fluctuations on ~50 comoving Mpc scales. However, the amount of heating can be much larger if the spectrum is harder. I discuss how temperature fluctuations from HeII reionization bias measurements from the HI Lyman-alpha forest of the IGM temperature and of cosmological parameters, and I quantify the detectability of these fluctuations with wavelet statistics. I conclude by contrasting the morphology of HeII reionization by quasars with that of hydrogen reionization by stars.
Oct. 27, Monday 12:10 pm (TAC seminar)
Adrienne Erickcek, Caltech
544 Campbell Hall
"Structure Beyond the Horizon: Inflationary Origins of the Cosmic Power Asymmetry"
WMAP measurements of CMB temperature anisotropies reveal a power asymmetry: the average amplitude of temperature fluctuations in one hemisphere is larger than the average amplitude in the opposite hemisphere at the 99% confidence level. This power asymmetry may be generated during inflation by a large-amplitude superhorizon perturbation that causes the mean energy density to vary across the observable Universe. Such a superhorizon perturbation would also induce large-scale temperature anisotropies in the CMB; measurements of the CMB quadrupole and octupole (but not the dipole!) therefore constrain the perturbation's amplitude and wavelength. I will show how a superhorizon perturbation in a multi-field inflationary theory, the curvaton model, can produce the observed power asymmetry without generating unacceptable temperature fluctuations in the CMB. I will also discuss how this mechanism for generating the power asymmetry will be tested by forthcoming CMB experiments.
Oct. 28, Tuesday 1:10 pm
Julio Navarro, U. Victoria
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"The Aquarius Project: Dark Matter under a Numerical Microscope"
The Aquarius Project is a series of cosmological simulations designed to study the clustering of Cold Dark Matter on the smallest scales of astrophysical relevance. I will report on our latest results, which include the first billion-particle simulation of a galactic halo. This simulation probes reliably the structure of Milky Way-sized objects down to 100 pc, and its substructures down to 10^5 Msun. I will discuss some applications of these results, with emphasis on the interpretation of galaxy rotation curves and on strategies for the identification of a potential dark matter annihilation signal in the gamma-ray sky.
Oct. 30, Thursday 4:00 pm (RPM)
Lexi Moustakas ,JPL
LBL 50A-5132
"Strong gravitational lensing probes of dark matter"
Abstract: The nature of dark matter remains a profound problem in our understanding of the universe. Though the census of dark matter is fairly robust, the plausible range of properties that a candidate particle may have is broad enough to allow for many possibilities. The distinctions between candidates may manifest themselves at relatively modest astrophysical mass-scales, which may be probed by strong gravitational lensing, uniquely so at cosmological distances. Complementary observations of even a single strong lens can probe different moments of the "substructure" mass function, over a very large range of mass-scales. I will present the theory of substructure probes in lenses, including new work on time-delay perturbation studies, and will discuss the power of current and future observations (and the need for new concrete theoretical predictions) for tackling the problem of dark matter. This work leads to a new mission concept that would be dedicated to this goal.
September 2008:
Sep. 2, Tuesday 1:10 pm
Andisheh Mahdavi , SFSU
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Multiwavelength Observations of Galaxy Clusters"
Clusters of galaxies are dominated by dark matter. We can see the gravitational effect of this dark material on the orbits of cluster members, the thermodynamics of the hot gas, and the shapes of galaxies behind the cluster. I will argue that combining multiwavelength data for a single relaxed cluster can yield powerful constraints on its dark matter distribution and on the equation of state of the intracluster plasma. At the same time, multiwavelength observations of merging clusters can yield significant and perhaps even more interesting constraints on dark matter properties. Both relaxed and merging clusters are well-represented in the Canadian Cluster Comparison Project, an ongoing survey of fifty massive nearby clusters. I will conclude by discussing an unusual, massive, X-ray bright region devoid of galaxies at the core of Abell 520, and will address its implications for our understanding of the nature of dark matter.
Sep. 9, Tuesday 1:10 pm
Kyle Stewart, Irvine
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"The Merger Histories of LCDM Galaxies: disk survivability and the deposition of cold baryons via mergers "
We employ a high resolution LCDM N-body simulation to study the merger histories of galaxy-halos and the evolution of the merger rate with redshift. We confirm the existence of a 'universal' halo merger rate, and provide a slightly modified fitting formula as a function of halo mass, redshift, and merger mass ratio. We find that the majority of Milky Way-size halos have experienced at least one major merger (defined either as mass ratio > 1:3, or in terms of absolute mass m > 10^11 Msun/h), which raises concerns about the survivability of disk dominated galaxies in a LCDM universe.
We go on to explore the baryonic content of these mergers using direct empirical constraints to assign statistically likely stellar and gas masses to the central galaxies within the halos of our simulations. We find that the vast majority of mergers into Milky-Way size halos at z>1 are very gas rich (gas fraction > 50%). If we presume that gas rich-mergers such as these may result in disk dominated galaxies (as has been suggested based on direct numerical simulations), we find that only 20% of Milky Way-size galaxies have experienced a "destructive" gas poor major merger since z=2, suggesting a possible explanation to the problem of disk survivability. We also measure the total deposition of cold baryons into galaxies via mergers and find that Milky Way-size galaxies have accreted approximately 30% of their current cold baryonic mass directly from major mergers since z=2, the majority of which is gaseous. Whether this deposited material is labeled to be a "cold flow" is ! subject to definition, but it seems almost empirically inevitable that direct cold gas deposition of this kind must occur.
Sep. 11, Thursday 4:00 pm (RPM)
Adam Bolton ,Hawaii
LBL 50A-5132
"The Sloan Lens ACS Survey"
The Sloan Lens ACS (SLACS) Survey has combined SDSS spectroscopy with Hubble Space Telescope imaging to assemble an unprecedented sample of 70 galaxy-scale strong gravitational lenses. I will review the observational and scientific results of SLACS, with a particular focus on the mass-density structure and empirical scaling relations of elliptical galaxies. My talk will be aimed primarily at "non-lensers", and will feature both novel quantitative results and stunning astronomical images.
Sep. 16, Tuesday 1:10 pm
Devdeep Sarkar, Irvine
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Measuring Dark Energy and Primordial Non-Gaussianity: Things To (or Not to?) Worry About!"
I will first talk about measurements of Dark Energy Equation of State (EOS) via observations of Type Ia supernovae (SNe Ia) and the related challenges. In this context, I will concentrate on a couple of potential sources of systematic uncertainties: (1) systematics based on the idea of the existence of two different SN Ia populations. and (2) systematics incorporated due to gravitational lensing of supernovae. I will discuss the current status and expectations from upcoming surveys.
I will then discuss the effect of weak gravitational lensing on the measurement of the cosmic microwave background (CMB) primary bispectrum. The CMB bispectrum is a well-known probe of the non-Gaussianity of primordial perturbations. Just as the intervening large-scale structure modifies the CMB angular power spectrum through weak gravitational lensing, the CMB primary bispectrum generated at the last scattering surface is also modified by lensing. I will argue that for a high resolution experiment such as Planck, the lensing modification to the bispectrum must be properly included when attempting to estimate the primordial non-Gaussianity.
Sep. 18, Thursday 4:00 pm (RPM)
Angela Olinto , Chicago
LBL 50A-5132
"The highest energy particles"
After almost a century of observations, we still don't know the origin of the highest energy cosmic rays but the possibilities have narrowed down with the discovery that the ultra-high energy sky displays an anisotropic distribution in arrival directions. A significant correlation between the arrival directions of ultra-high cosmic rays measured by the Pierre Auger Observatory and the distribution of nearby active galactic nuclei signals the dawn of particle astronomy. We will discuss these historic results and their implications both for astrophysics and particle physics. Future projects on the field will also be addressed.
Sep. 23, Tuesday 1:10 pm
Laurie Shaw , McGill
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Cosmological Simulations for Sunyaev-Zel'dovich Cluster Surveys"
Measuring the mass and redshift distribution of clusters of galaxies provides us with a sensitive means of constraining cosmological parameters. Sunyaev-Zel'dovich experiments such as the South Pole Telescope aim to survey a large fraction of the sky searching for clusters via their SZ imprint on the CMB. In order to improve existing constraints it is vitally important that we understand the cluster selection function and contamination rate and can accurately infer the mass of clusters via measurements of their SZ flux. In the first part of this talk I will present a detailed analysis of the slope, normalisation and intrinsic scatter in the SZ flux - mass scaling relation using semi-analytic and simulated cluster samples. I will discuss the results of this analysis in the context of measurements of the halo mass function. In the second part, I will present work I have done to evaluate the cluster selection function, sample completeness and contamination for surveys such as SPT, using synthetic SZ sky-maps constructed from a high-resolution cosmological 'lightcone' simulation. Finally I will discuss how one might combine SZ and optical data to reduce sample contamination and obtain a more precise estimation of the cluster mass function.
Sep. 30, Tuesday 1:10 pm
Mark Voit , Michigan State
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Mysteries of Cluster Cores"
Current models of galaxy clusters can reproduce many of their observed characteristics but fail miserably in the core regions. If we wish to use clusters for precision cosmology, it would be wise to understand why those models fail. Feedback from supermassive black holes is thought to be a big part of the solution and also seems to be critical for understanding the properties of the universe's most luminous galaxies, which lie at the centers of galaxy clusters. I will present results from a large Chandra archival study of cluster cores showing that star formation and AGN behavior in central cluster galaxies is closely linked with the properties of the intracluster medium. The results of this survey suggest that electron thermal conduction determines the phase structure of the intracluster medium and might be an important channel for distributing AGN feedback throughout the cluster core.

August 2008:
Aug. 1, Friday 12:00 pm
Jason Prochaska , UCSC
LBL 50-5026
"Baryons: What, When and Where?"
A review the current state of empirical knowledge of the total budget of baryonic matter in the Universe as observed since the epoch of reionization. Our summary examines on three milestone redshifts since the reionization of H in the IGM, z = 3, 1 and 0 with emphasis on the endpoints. We review the observational techniques used to discover and characterize the phases of baryons. In this talk, I will emphasize the open questions regarding this research, of which there are embarrassingly many. See astro-ph/0805.4635 for a write-up of this material.
July 2008:
July 18, Friday 12:00 noon
Eric Gawiser, Rutgers
LBL Bldg. 50, room 5026 (INPA common room)
"Probing the Dark Matter-Galaxy Formation Connection with Lyman Alpha Emitting Galaxies"
I will describe how our understanding of cosmological structure formation is used to probe the dark matter properties of high-redshift galaxies and to identify their present-day descendants. We studied the clustering properties and multiwavelength spectral energy distributions of a complete sample of 162 Lyman Alpha Emitting (LAE) galaxies at z=3.1 discovered in deep narrow-band imaging of the MUSYC-ECDFS field. The LAEs exhibit a moderate clustering bias of b=1.7, which implies median dark matter halo masses of 1011 M_sun. The evolution of galaxy bias with redshift predicts that z=3.1 LAEs evolve into typical present-day galaxies with L~=L*, whereas other z>3 galaxy populations, including Lyman Break Galaxies and Active Galactic Nuclei, typically evolve into more massive galaxies. A two-population fit to the LAE spectral energy distribution finds that the typical LAE has low stellar mass (109 M_sun), moderate star formation rate (2 M_sun/yr), a young component age of 20 Myr, and little dust (A_V<0.2). This represents our first direct knowledge of the progenitors of spiral galaxies like the Milky Way seen when the universe was only 2 Gyr in age.
References: Gawiser et al. 2007 (ApJ 671, 278), Francke et al. 2008 (ApJL 673, 13)
July 29, Tuesday 1:10 pm
Alessandro Melchiorri , Rome
LBL 50B-4205
"New Constraints on the Cosmic Neutrino Background"
A survey is made of the most recent constraints on Neutrino parameters from several cosmological observables. In particular, we discuss the latest cosmic bounds on the neutrino mass and their interplay with the final 0nu2beta decay results in 76-Ge claimed by part of the Heidelberg-Moscow Collaboration. Moreover, we search for the presence of cosmological neutrino background anisotropies in recent WMAP 5-year data and show that independent determinations of the age of the universe in combination with CMB data can provide the most stringent constraint on the effective number of neutrino species.

Cosmology Seminars in Previous Years

   
            
 
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