2011-2012 Seminars 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:


Past Months

(Previous years)
June 2012:
June 7, Thursday 4:00 pm (RPM)
Eric Linder, LBNL
50A-5132
"Chasing Down Cosmic Acceleration"
In the last 15 years of observations we have ruled out the simplest new physics origins for cosmic acceleration. We have also learned much better what questions to ask and what data is needed to answer them. I discuss recent trends useful for theorists and observers, including ideas tied closely to gravity and particle physics, and complementarity between supernovae, large scale structure, and CMB surveys. Presenting new calculations on what is the strongest path to further progress within the next 5 years, I see the chase closing in more quickly than previously thought.
May 2012:
May 1, Tuesday 1:10 pm
Gianni Bernardi, CfA
Hearst Field Annex, B5
"How far are we from detecting the 21cm line from the Epoch of Reionization?"
The redshifted 21 cm line is likely to be the best observational probe of one of the most important phase transitions of the Universe: The birth of the first luminous objects which ionized the intergalactic medium. The very few observational data available suggest that the transition might have started around z ~ 13 and ended around z ~ 6-7. The overall picture remains still undefined due to the intrinsic observational difficulties and a new generation of radio telescopes are under construction to fill this gap through the measurement of the redshifted 21 cm line from neutral Hydrogen. In my talk I will give an overview of the observational issues and status related to the redshifted 21 cm line. I will present updates on the status of three ongoing experiments: LOFAR-EoR, MWA and LEDA.
POSTPONED! May 3, Thursday 4:00 pm (RPM) 50A-5132

May 8, Tuesday 1:10 pm
Steve Furlanetto, UCLA
Hearst Field Annex, B5
"Piecing Together the Epoch of Reionization"
The era of the first galaxies and reionization is one of the final frontiers of observational cosmology. At the moment, a wide range of observations provide tantalizing - but often confusing - clues. I will summarize our current knowledge about this epoch and its low-redshift analog, when helium is fully ionized. I will then describe how future observations can settle some of the important open questions that remain. When did reionization occur? What sources were responsible? How did the intergalactic medium affect the process? And what did it do to future generations of sources?
May 29, Tuesday 4:00 pm (RPM)
Cameron McBride, Harvard
50A-5132
"Baryon Acoustic Oscillations with BOSS"
In this talk, I will focus on the first cosmological constraints utilizing the "standard ruler" of the baryon acoustic oscillation (BAO) feature as detected in the Baryon Oscillation Spectroscopic Survey (BOSS) from the SDSS-III project. I will discuss the cosmological constraints and the context of these results with previous measurements to construct a cosmic distance ladder. This data release (DR9) is the largest sample of galaxy redshift data ever used to constrain the BAO, covering an effective volume of 2.2 cubic gigaparsecs with 264,283 massive galaxies. I will briefly review our joint analysis of both the correlation function and power spectrum where we identify the BAO feature at a significance of over 5 sigma, yielding a BAO position to 1.7% accuracy. We use a series of detailed mock galaxy catalogs to justify our methods, including the application of density reconstruction to fully harness the statistical power of the data. Finally, I will comment on some plans for future BOSS analyses.
May 31, Thursday 4:00 pm (RPM)
Beth Reid, LBNL
LBL 50B-4205
"Cosmology with Redshift Space Distortions Measured by BOSS"
This talk will complement "Baryon Acoustic Oscillations with BOSS", and describe in detail the other information we extract from our measurement of the galaxy correlation function at z=0.57 from the BOSS DR9 sample. Further cosmological tests are available from the relative amplitude of clustering along and perpendicular to the line of sight. The Alcock-Paczynski effect allows a geometric test to measure the product of the angular diameter distance and Hubble expansion rate at the galaxy sample's redshift. Peculiar velocities of galaxies also amplify the apparent clustering along the line-of-sight. We demonstrate our ability to distinguish these effects in the data through their scale-dependence, and present measurements of both the growth of structure, the angular diameter distance, and the Hubble expansion rate at z=0.57, along with their cosmological implications.

April 2012:
Apr. 3, Tuesday 1:10 pm
Lam Hui, Columbia
Hearst Field Annex, B5
"Equivalence principle and cosmic acceleration"
Theories that attempt to explain the observed cosmic acceleration by modifying gravity on large scales generally introduce a new long range force, typically mediated by a scalar. We will explain the fundamental reason behind the ubiquitous nature of this scalar force. Such a force has to be screened on solar system scales to satisfy existing experimental constraints, but can lead to O(1) violations of the equivalence principle in other environments. We will discuss what these environments might be where suitable astrophysical tests can be carried out.
Apr. 5, Thursday 4:10 pm (Astronomy Colloquium)
Julianne Dalcanton, Washington
1 Le Conte
"Galaxies Viewed as Collections of Individual Stars"
In extragalactic astronomy, we routinely observe galaxies in broad-band filters, and then interpret the resulting spectral energy distribution to learn about the galaxies' masses, star formation rates, ages, and metallicities. The fidelity of this interpretation relies on having a detailed understanding of the stellar populations within the galaxy, and on accurately characterizing the luminosities and colors of the billions of stars which contribute to a galaxy's light. In this talk I will discuss several large programs which use the Hubble Space Telescope to resolve millions of the most luminous stars in nearby galaxies. I will highlight results using near infrared observations, focusing on implications for the evolution of stars and the integrated NIR light of distant galaxies.
Apr. 6, Friday 12:00 pm (INPA Journal Club)
Christian Reichardt, UCB
LBL 50-5026 (INPA room)
"A new look at the epoch of reionization with the South Pole Telescope "
The South Pole Telescope (SPT) is a 10-meter telescope designed to survey the millimeter-wave sky, taking advantage of the exceptional observing conditions at the Amundsen-Scott South Pole Station. The telescope and its ground-breaking 960-element bolometric camera were successfully installed at the South Pole in 2007. Since then, SPT has embarked upon a large, three-frequency survey covering 6% of the entire sky. I will report on the multi-frequency power spectrum results for this survey, including a detection of the thermal Sunyaev-Zel'dovich (SZ) power and improved upper limits on the kinetic SZ power. I will discuss how we can use the kinetic SZ power and CMB polarization data to determine when the epoch of reionization began, when it ended and how long it lasted.
Apr. 10, Tuesday 1:10 pm
Ruth Pearson, Sussex/SLAC
Hearst Field Annex, B5
"CMB lensing and primordial squeezed non-Gaussianity"
Squeezed primordial non-Gaussianity can strongly constrain early-universe physics, but it can only be observed on the CMB after it has been gravitationally lensed. We give a new simple non-perturbative prescription for accurately calculating the effect of lensing on any squeezed primordial bispectrum shape, and test it with simulations. We give the generalization to polarization bispectra, and discuss the effect of lensing on the trispectrum. We explain why neglecting the lensing smoothing effect does not significantly bias estimators of local primordial non-Gaussianity, even though the change in shape can be ~ 10%. We also show how fNL trispectrum estimators can be well approximated by much simpler CMB temperature modulation estimators, and hence that there is potentially a ~ 10-30% bias due to very large-scale lensing modes, depending on the range of modulation scales included. Including dipole sky modulations can halve the fNL error bar if kinematic effects can be subtracted using known properties of the CMB temperature dipole. Lensing effects on the gNL trispectrum are small compared to the error bar. In appendices we give the general result for lensing of any primordial bispectrum, and show how any full-sky squeezed bispectrum can be decomposed into orthogonal modes of distinct angular dependence.
Apr. 12, Thursday 4:10 pm (Astronomy Colloquium)
James Bullock, Irvine/UCB
1 Le Conte
"Dark Matter, Dwarf Galaxies, and Massive Failures in the Halo of the Milky Way"
The favored dark energy plus cold dark matter (LCDM) model of cosmology predicts that the Milky Way should be surrounded by thousands of dark matter satellite clumps, in great excess of the observed count of Galactic dwarf satellite galaxies. This mismatch is known as the "missing satellite problem". Recent discoveries in theSloan Digital Sky Survey have revealed a new population of ultra-faint dwarf satellites, motivating excitement within the community that some "missing" LCDM satellites are finally being found. Unfortunately for the theory, the situation is not quite so rosy once the dynamical masses of the known satellites are considered. Specifically, the majority of the most massive dark matter satellites predicted to exist are too dense to host any of the bright satellite galaxies of the Milky Way. This poses a serious puzzle theoretically: either galaxy formation becomes effectively stochastic on scales smaller than ~0.1L* or the central densities of dark matter subhalos are significantly lower than predicted in dissipationless simulations. I discuss some possible solutions to this puzzle from the standpoint of baryonic physics and non-standard dark matter physics.
Apr. 17, Tuesday 1:10 pm
Joe Hennawi, MPIA
Hearst Field Annex, B5
"Quasars Probing Quasars: Circumgalactic Gas in Absorption and Emission"
I will argue that observations of the diffuse gas in the outskirts of galaxies, the so called circumgalactic medium, are essential for constraining the 'initial conditions' for galaxy formation. Such observations provide a fruitful comparison to theory, because hydrodynamics at moderate overdensities is much easier to simulate than molecule or star-formation. A novel technique will be introduced, whereby a foreground quasar (and massive galaxy) can be studied in absorption against a background quasar, resolving scales as small as 30kpc. This experiment reveals a rich absorption spectrum which contains a wealth of information about the physical conditions of diffuse gas around massive proto-galaxies. I will summarize the implications of these new measurements in the context of galaxy formation models, and discuss the possibility of detecting cooling radiation in emission from the gas we study in absorption.
Apr. 24, Tuesday 1:10 pm
Priya Natarayan, Yale
Hearst Field Annex, B5
"The formation of massive black hole seedss"
It appears that a new channel to form black seeds might be required in order to explain the observed supermassive black holes at high and low redshift. I will discuss new theoretical work on the formation of massive seeds at early epochs and their observational consequences.
March 2012:
Mar. 1, Thursday 4:10 pm (Astronomy Colloquium)
Brian Siana, Riverside
1 Le Conte
"Finding and Characterizing the Sources of the Ionizing Background with Keck and HST"
It is believed that star-forming galaxies are responsible for reionizing the hydrogen in the intergalactic medium at z > 7, primarily because there are no other viable candidates. The hydrogen- ionizing emissivity is dependent upon two factors: the star formation rate density and the fraction of ionizing photons that escapes the galaxies. The star formation rate density is still uncertain at z > 2 due to the uncertain number of faint sources beyond the detection limits. In addition, the escape fraction of ionizing photons still remains a mystery. Nearly every attempt to directly measure the ionizing emission from galaxies has returned null results, and the few viable detections often have peculiar properties. One thing is clear, if star-forming galaxies reionized the universe and provide the ionizing background thereafter, it must be the very faint galaxies that are responsible. I will discuss ongoing campaigns with Keck and HST to 1) find and characterize the very faint galaxies which are analogous to those that reionized the universe and 2) directly detect escaping ionizing radiation from them.
Mar. 6, Tuesday 1:10 pm
Smadar Naoz, Harvard
Hearst Field Annex, B5
"Emerging from the Dark Ages, The role of Baryons in Structure Formation"
In recent years, the first and last chapters of the cosmic story have been unfolded. Observations of the cosmic microwave background radiation have revealed the chapter in the history of the Universe that took place only a few hundred thousand years after the Big Bang. The last chapter has been uncovered using observations of the morphology, and distribution of galaxies in the local Universe. However, the main event of the story is still missing. Basic questions regarding the transformations of the uniform early gas into the galaxies we see today, and what were the different properties of these objects, are still open. We study the gas content of halos in the early universe in the linear and non linear regime, using both analytical calculations and high resolution hydrodynamical simulations. We find that baryons play a crucial role in structure formation and evolution. Specifically we find that the effect of pressure in the formation of the first galaxies is only moderate. We also test the effects of the relative velocity between the baryons and the dark matter on high-z structure formation. We have quantified statistically this effect using simulations and found that the total halo mass function as a function of mass is significantly suppressed in all of our simulation sets. Our most significant result is the high fraction of halos that are almost entirely devoid of gas.
Mar. 13, Tuesday 1:10 pm
Salman Habib, Argonne
Hearst Field Annex, B5
"Computing the Dark Universe"
Large-area sky surveys provide a wealth of cosmological information. Some of the results can be interpreted using analytical methods but, by and large, the use of N-body simulations -- individually, or in combination with analytical modeling -- has proven to be crucial in this effort. As statistical error bars from survey observations continue to shrink, simulations are entering a new regime in their use as analysis and prediction tools. Additionally, coming changes in supercomputer architectures provide another rationale for developing new simulation and analysis capabilities. In this talk I will describe the motivations behind the development of the HACC (Hardware/Hybrid Accelerated Cosmology Code) framework, its current status, including some recent results, and plans for the future.
Mar. 14, Wednesday 1:00 pm (mini-CDI Seminar)
Katrin Heitmann, Argonne
1011 Evans Hall
"Exploring the Dark Universe: Computational, Statistical, and Data Challenges "
Cosmology -- the study of the origin, evolution, and constituents of the Universe -- is in a scientifically very exciting phase. Two decades of surveying the sky have culminated in the celebrated ``Cosmological Standard Model''. Yet, two of its key pillars, dark matter and dark energy -- together accounting for 95% of the mass-energy of the Universe -- remain mysterious. Deep fundamental questions demand answers: What is dark matter made of? Why is the Universe's expansion rate accelerating? Should general relativity be modified? What is the nature of primordial fluctuations? What is the exact geometry of the Universe? To address these burning questions, survey capabilities are being exponentially improved. Next-generation observatories will open new routes to understand the true nature of the ``Dark Universe''. These observations will pose tremendous challenges on many fronts -- from the sheer size of the data that will be collected (more than a hundred Petabytes) to its modeling and interpretation. The interpretation of the data requires sophisticated simulations on the world's largest supercomputers. The cost of these simulations, the uncertainties in our modeling abilities, and the fact that we have only one Universe that we can observe opposed to carrying out controlled experiments, all come together to create a major test for computational, statistical, and data analysis methods.
In this talk I will give a very brief introduction to the Dark Universe and outline the challenges ahead. To combat these challenges, close cross-disciplinary collaborations between physicists, statisticians, and computer scientists will be crucial. I will discuss two examples of successful collaborative work and propose new tasks where cosmologists urgently need help from the data and statistics community.
Mar. 15, Thursday 4:10 pm (Astronomy Colloquium)
Jim Peebles, Princeton
1 Le Conte
"The Curious Behavior of Galaxies as Island Universes"
The evolution of a galaxy typically is strikingly insensitive to ambient conditions, contrary to a straightforward reading of the behavior of dark matter in the standard LCDM cosmological model. Maybe this is because galaxy evolution is far too complex to be read in a straightforward way, but that path is tortuous enough to motivate consideration of how LCDM might be altered to preserve agreement with the cosmological tests but allow galaxies to behave as better approximations to island inverses. I will present an example, the addition of evanescent dark matter to LCDM.
Mar. 20, Tuesday 1:10 pm
Tristan Smith, UCB
Hearst Field Annex, B5
"Looking for cracks in the standard cosmological model: neutrinos and non-Gaussianity"
The cosmic microwave background (CMB) has provided us the laboratory in which we entered the era of 'precision cosmology'. By and large these observations have confirmed the basic, standard, cosmological model which supposes a universe seeded with Gaussian initial fluctuations and filled with non-relativistic matter, photons, and 3 neutrino species. As observations have become more accurate it has become increasingly pertinent to test some of the assumptions that have gone into building the standard cosmological model. In this talk I will present some of my recent work on testing these assumptions.
First I will discuss how recent measurements of the small-scale CMB have hinted at the presence of extra relativistic energy density within the universe. Any interpretation of these results will necessitate the measurement of some of the properties of any extra relativistic energy density. Using recent small-scale measurements of the CMB, along with my colleagues, we have been able to constrain the clustering properties of the extra relativistic energy density. We show that current observations disfavor the interpretation that any extra relativistic energy consists of standard neutrinos.
Second, there has been an increasing interest in testing whether the initial fluctuations follow Gaussian statistics. These tests of 'primordial non-Gaussianity' use estimators constructed from either the CMB three-point (bispectrum) or four-point (trispectrum) correlation functions. Usually an estimator constructed from data is assumed to have a Gaussian probability distribution (PDF) as a result of the central limit theorem. However, in this case the central limit theorem does not apply since the number of terms that appear in these estimators are much greater than the number of measurements. A complete knowledge of the shape of the PDF is necessary in order to properly assign confidence limits to any constraint. I will discuss how Monte Carlo simulations show that the PDF for these estimators are highly non-Gaussian themselves, necessitating more care in using these estimators, especially for future observations with the Planck satellite. I will also show how the constraining power of these estimators may be improved by using a realization-dependent normalization.
Mar. 22, Thursday 4:10 pm (Astronomy Colloquium)
Chris Stubbs, Harvard
1 Le Conte
"The Dark Energy Crisis in the Longer Termm"
The discovery of the accelerating expansion of the Universe, driven by "Dark Energy", is an indication that our understanding of fundamental physics is incomplete. In particular, the Dark Energy mystery lies at the intersection of gravity and quantum mechanics where we have trouble knitting together a consistent theoretical picture. In some ways our current situation is similar to the circumstances before the advent of quantum mechanics, with experimental results that don't fit into our existing theoretical framework. I will present an overview of the Dark Energy crisis we face, review some of the work in progress, and sketch out some scenarios that might lie in our longer term future.
Mar. 27, Tuesday Spring Break

March 30, Friday 12:00 pm (INPA Journal Club)
Nick Hand, UCB
LBL 50-5026 (INPA room)
"The detection of galaxy cluster motions using data from the Atacama Cosmology Telescope and BOSS"
Using microwave sky maps from the Atacama Cosmology Telescope (ACT), the motions of galaxy clusters and groups were recently detected for the first time using CMB temperature distortions due to the kinematic Sunyaev-Zel'dovich effect.The positions of galaxy clusters in the ACT data were identified by their constituent luminous galaxies observed by the Baryon Oscillation Spectroscopic Survey. The mean pairwise momentum of clusters was measured at high statistical significance. I will discuss the methodology and results of this analysis in the context of the standard cosmological model and will comment on possible continuations of this analysis in the future.
February 2012:
Feb. 7, Tuesday 1:10 pm
Peter Sorenson, LLNL
Hearst Field Annex, B5
"Towards direct detection of dark matter: recent results from XENON10, anticipated results from LUX"
Although the XENON10 liquid xenon TPC detector ceased operation in 2007, among the data it acquired was a low-energy-threshold exposure which recently (2011) was able to place the strongest bounds on low-mass (< 10 GeV) WIMP parameter space. I will discuss this analysis, and prospects for the next-generation LUX detector.
Feb. 7, Tuesday 4:00 pm (RPM)
Dustin Lang, Princeton
LBL 50A-5132
" 'the Tractor': Measuring Astronomical Objects in Collections of Images"
"the Tractor" is a new project to frame astronomical source detection and measurement as an inference problem in a pixel-level generative (forward) model. This approach naturally handles the multi-band, many-epoch data sets that will be produced by surveys such as Pan-STARRS, the Dark Energy Survey, and the Large Synoptic Survey Telescope (LSST), but it is also well suited to more diverse imaging sets from different instruments and different wavelengths. Unlike traditional approaches, we avoid co-adding, degrading, or discarding any of the images; the goal is to make use of the (often complementary) information in all the images. This strength of the Tractor makes it ideally suited to producing the accurate wide-area photometric catalogs required for targeted spectroscopic surveys such as BigBOSS.
Feb. 9, Thursday 4:00 pm (RPM)
Xiaoying Xu, Arizona
LBL 50A-5132
"A 2% Distance to z=0.35 by Reconstructing Baryon Acoustic Oscillations"
We demonstrate the first application of reconstruction to a galaxy redshift survey using the observed galaxies in the SDSS DR7 luminous red galaxy catalogue. Our reconstruction procedure is analogous to running gravity backwards and aids in obtaining a more precise measurement of the acoustic scale. We validate our reconstruction, covariance matrix and fitting techniques on 160 mock catalogues derived from the LasDamas simulations in redshift space. We then apply these techniques to the DR7 LRG sample and find that the error on the acoustic scale decreases from ~3.5% before reconstruction to ~1.9% after reconstruction. This factor of 1.8 reduction in the error is equivalent to the effect of increasing the survey volume by about a factor of 3. We also see an increase by at least 1-sigma in the significance of our BAO detection for 2 different measures of BAO significance. Using our distance measure to constrain cosmology, we find our data is consistent with a standard LCDM universe. However, our data may show slight hints that the number of relativistic neutrino species is higher than currently thought.
Feb. 10, Friday 12:00 pm (INPA Journal Club)
Justin Vandenbroucke, Stanford
LBL 50-5026 (INPA room)
"Antiparticles in the shadow of the Earth: cosmic-ray positrons with the Fermi Gamma-ray Space Telescope"
Cosmic rays are primarily protons and other nuclei, but there is a small flux of electrons and an even smaller flux of positrons. Cosmic-ray positrons can be produced by astrophysical accelerators, by collisions of cosmic-ray protons with interstellar gas, or by dark matter annihilation. We used the Fermi Gamma-ray Space Telescope to measure the charge-separated electron and positron energy spectra. Because Fermi does not have an onboard magnet, we used the Earth's magnetic field to distinguish positrons and electrons. We confirmed the PAMELA discovery that the positron fraction is rising with energy between 10 and 100 GeV and measured the positron flux for the first time in the 100-200 GeV range. Explaining the positron excess remains an outstanding question.
Feb. 13, Monday 12:10 pm (TAC seminar)
Claude-Andre Faucher Giguere, UCB
Hearst Field Annex, B1
"Inflows, outflows, and the physics of galaxy formation"
Galaxies must continuously accrete gas from the intergalactic medium in order to maintain their star formation rates. At the same time, star-forming galaxies and their black holes drive powerful winds that dramatically affect their evolution. Inflows and outflows are thus among the key physical processes of galaxy formation, tying together the vastly different scales involved. I will first summarize the inflow predictions from cosmological simulations and show how they can be tested observationally. In doing so, I will address the physical nature of Ly-alpha blobs and Lyman limit absorbers. Motivated by breakthrough discoveries of massive, galaxy-scale outflows driven by AGN in the last year, I will then address two puzzles raised by the data: the extreme multiphase structure of atomic outflows, and the large momentum fluxes inferred. The talk will conclude by outlining advances that will dramatically improve the realism and predictive power of theoretical studies of galaxy formation in the next few years.
Feb. 14, Tuesday 11 am,
Nick Ball, Herzberg Institute for Astrophysics
1011 Evans Hall
"Data Mining to Perform Novel Science on Large Astronomical Datasets"
I will give an overview of my work since 2004 on using data mining to perform novel science on large astronomical datasets, focusing on (1) Morphological galaxy classification in the Sloan Digital Sky Survey (SDSS) using artificial neural networks; (2) Star-galaxy separation in the SDSS using decision trees; (3) Photometric redshifts of SDSS and Galaxy Evolution Explorer quasars using k nearest neighbors; and (4) Separation of galaxies that are Virgo members from those in the background using unsupervised clustering in the Next Generation Virgo Cluster Survey. Several of these represent somewhat pioneering studies that have much relevance to the current and future era of terascale and petascale data. For each study, I will provide a brief review of the result, then relate the result to more recent developments and possible future directions. Finally, I will provide a few general remarks on the current state of Astroinformatics, and its future prospects, from the point of view of an astronomer who utilizes data mining.
Feb. 14, Tuesday 12:35 pm, note special time!
Evan Scannapieco, Arizona State
Hearst Field Annex, B5
"Modeling Turbulence in Starbursting Galaxies"
The interstellar medium (ISM) that pervades starbursting galaxies is a multiphase distribution in which turbulent support is at least as important as thermal pressure, and turbulence is often supersonic. I will present three numerical studies that model key aspects of this medium: (i) simulations of isotropic, supersonic turbulence, which shed new light on the mixing of heavy elements into the ISM; (ii) simulations of stratified, radiatively-cooled turbulence, which uncover a fundamental ISM transition at a critical turbulent velocity of 35 km/s; (iii) galaxy-scale simulations that use a subgrid approach to deposit supernovae energy directly into supersonic turbulence, leading to a collective central outflow as observed in NGC 1569 and other outflowing starbursts.
Feb. 23, Thursday 4:10 pm (Astronomy Colloquium)
Rebecca Bernstein, Santa Cruz
Le Conte

Feb. 27, Monday 3:10 pm (RAL seminar)
Aaron Parsons, UCB
Hearst Field Annex, B5
"A Low-Frequency Radio Astronomy Battle Plan"
Events have been unfolding quickly in the (non-violent) war to conquer the radio sky below 1GHz. Several new projects have taken the field or are advancing rapidly toward funding, particularly in the areas of using 21cm emission to study the pre-reionization dark ages (e.g. LEDA) and baryon acoustic oscillations post-reionization (e.g. BAOBAB). Leading facilities such as GMRT and LOFAR are beginning to crank out new, high-quality observations routinely, while PAPER remains committed to being a focused experiment making an end-run for reionization. The MWA had a headstart, has hit some rough terrain, and yet continues to march forward. Meanwhile, South Africa and Australia are in a final bout to win SKA siting by championing their respective low-frequency progenitors (i.e. PAPER and MWA). HERA and SKA-low await the victors in this battle royale. Who will win? Who will lose? All we know is that the radio sky will never look the same again.
Feb. 28, Tuesday 1:10 pm
Vuk Mandic, Minnesota
Hearst Field Annex, B5
"Cosmology and Astrophysics with Gravitational-Wave Detectors"
Gravitational waves are predicted by the general theory of relativity to be produced by accelerating mass systems with quadrupole (or higher) moment. The amplitude of gravitational waves is expected to be very small, so the best chance of their direct detection lies with some of the most energetic events in the universe, such as mergers of two neutron stars or black holes, core collapse Supernovae, or the Big-Bang itself. The Laser Interferometer Gravitational-wave Observatory (LIGO) has built three gravitational-wave detectors designed to search for these astrophysical and cosmological signals. I will review the current status of LIGO detectors, as well as some of their most recent results. I will also discuss plans and expectations for the future generations of gravitational-wave detectors.
January 2012:
Jan 17, Tuesday 12:10 pm NOTE SPECIAL TIME!
Fergus Simpson, Edinburgh
Physics: Old Le Conte 325
"Testing the Laws of Gravity with CFHTLenS and WiggleZ"
The observed presence of dark energy may be the first sign of new physics in the Universe, either in the form of a matter-energy component or by revising Einstein gravity. Weak gravitational lensing and galaxy peculiar velocities provide complementary probes of modifications to General Relativity, and in combination allow us to test theories of gravity in a unique way. We perform such an analysis by combining measurements of the growth of structure from the WiggleZ Dark Energy Survey with cosmic shear tomography from CFHTLenS, producing the strongest existing constraints on the metric potentials that describe general theories of gravity.
Jan 19, Thursday 4:00 pm (RPM)
Ashley Ross, Portsmouth
LBL 50A-5132
"The Information Content Encoded in the Clustering of Galaxies"
The clustering of galaxies encodes a wealth of information on the physical processes that have governed the evolution of the observable Universe from the big bang until today. This includes information on the process by which galaxies begin to and cease forming stars, the sum of neutrino masses, the matter density of the Universe, the expansion history of the Universe (and thus dark energy), and the degree of non-Gaussianity in the primordial matter density field. I will describe how we observe galaxies and make maps of their positions. I will describe how we can then measure clustering statistics using these maps and the relevance of measurements I have made to the science described above. Throughout, I will discuss and compare results obtained using both photometric and spectroscopic redshifts, the care that must be taken in order to ameliorate systematic errors, and the relevance of the results to the science goals of BOSS, DES, and BigBOSS.
Jan. 19, Thursday 4:10 pm (Astronomy Colloquium)
Jane Rigby, GSFC
1 Le Conte
"Status update on the James Webb Space Telescope project"
The James Webb Space Telescope (JWST) is a large (6.6 m), cold (<50 K), infrared optimized space observatory that will be launched in 2018. The observatory will have four instruments covering 0.6 to 28 micron, with scientific capabilities that include deep imaging, multi-object spectroscopy, integral field spectroscopy, and exoplanet coronagraphy and spectroscopy. I will review JWST's key science themes, as well as new ideas from the recent JWST Frontiers Workshop. I will summarize technical progress and mission status, including the status of each instrument, and the recent completion of mirror segment fabrication. I will summarize resources to learn more about the mission, including exposure time calculators and sensitivity charts.
Jan. 20, Friday 12:00 pm (INPA Journal Club)
Hong Guo, CWRU
LBL 50-5026 (INPA room)
"The Evolution of Galaxies on the Red Sequence and Blue Cloud in BOSS"
We analyze the evolution of the BOSS galaxies, especially the CMASS(constant mass) sample from redshift 0.4 to 0.7. We utilize the galaxy two-point correlation function as the main method to study the evolution of red and blue galaxies. The analysis focuses on the small scales(from 0.01 Mpc/h to 20Mpc/h), where the influence of fiber collision effect in the survey is corrected appropriately. We also investigate the clustering dependence on the different color and luminosity, and found consistent results with early works using SDSS DR7 data. While luminous red galaxies have the largest bias relative to the underlying dark matter field, its evolution however is not completely passive from redshift 0.4 to 0.7. We found strong evolution of red galaxies with redshift larger than 0.5. We will incorporate halo occupation distribution to study the evolution of central and satellite galaxies in order to determine the effect of merging in the CMASS sample.
Jan 24, Tuesday 1:10 pm
Chris Blake, Swinburne
Hearst Field Annex, B5
"Measuring Dark Energy With The Wigglez Survey"
We present new measurements of the cosmic expansion history and growth history over the last 7 billion years, using data from the WiggleZ Dark Energy Survey of 200,000 galaxy redshifts. We have used baryon acoustic oscillations (BAOs) in the galaxy distribution as a standard ruler to measure the distance-redshift relation up to z=0.73, and present a BAO "Hubble diagram" which provides a powerful cross-check of the use of Type Ia supernovae as standard candles. We additionally use redshift-space distortions in the galaxy clustering pattern to determine the cosmic growth rate with 10% accuracy in redshift bins up to z=0.9. We show that a cosmological constant model of dark energy is able to simultaneously fit both the expansion and growth data. Finally, we measure Alcock-Paczynski distortions in the clustering pattern to reconstruct the expansion history in a non-parametric manner, demonstrating the reality of accelerating cosmic expansion.
Jan. 24, Tuesday 4:00 pm (Galform)
Joakim Rosdahl, France
HFA B5
"Extended Lyman-alpha emission from cold accretion streams"
I present results from a set of cosmological simulations designed to study the observability of cold accretion streams at redshift 3 via Lyman-alpha (Lya) radiation and the feasibility of said streams as the driver of Lya blobs (or LABs). These simulations are unique because for the first time we include fully coupled radiative transfer of the UV radiation background with our newly developed RT version of the Ramses code and hence obtain a consistent model of self-shielding. This provides us with an accurate estimate of gas temperatures and neutral hydrogen fractions, which in turn allows us to accurately estimate the Lya emissivity of extended structures. I discuss the efficiency of gravitational heating in streams to power extended Lya emission and illustrate some of the complexities involved in extracting accurate observables from simulations. I show our overall resulting LAB luminosities and morphologies and compare with observations. Our main results are that the cold accretion streams in massive halos of >10^12 solar masses are capable of powering LABs and we predict that cold accretion streams should be unambiguously observable in the near future with upcoming instruments. (Based on arXiv:1112.4408v1.)
Jan. 24, Tuesday 4:00 pm (RPM)
Surhud More, Chicago
LBL 50A-5132
"Galaxy-Dark Matter Connection: A Cosmological Perspective"
The statistical properties of dark matter distribution in the Universe are crucially dependent on the parameters used to describe cosmology. The distribution of galaxies in the Universe traces the distribution of dark matter. Therefore, observations of galaxies can provide important information about the cosmological parameters. However, this requires an accurate knowledge of how the galaxy distribution is biased with respect to the dark matter distribution. We have developed a unique statistical tool, the conditional luminosity function (CLF) which can be used to specify how galaxies occupy dark matter halos and consequently specify the galaxy bias. The CLF can be used to predict various observables properties of the galaxy distribution. I shall focus on the abundance of galaxies, their clustering strength and the galaxy-galaxy lensing signal around them and present constraints on cosmological parameters obtained from a combination of these observables.
Jan. 25, Wednesday 1:30 pm (special INPA Journal Club)
Dmitry Prokhorov, Stanford
LB 50-5026 (the INPA common room)
"Perspectives in X-ray, SZ, and gamma-ray studies of clusters of galaxies"
I will discuss the possibilities to reveal non-equilibrium states behind merger shock fronts in galaxy clusters from X-ray observations, the 3D temperature structure of galaxy clusters from multi-frequency SZ observations, and extended gamma-ray emission of galaxy clusters from Fermi-LAT observations.
Jan. 26, Thursday 12:00 pm (INPA Journal Club)
Florian Beutler, Univ. of Western Australia
LB 50-5026 (the INPA common room)
"Large scale structure analysis with the 6dF Galaxy Survey"
In my talk I will present results of the large scale structure analysis with the 6dF Galaxy Survey (6dFGS). The large-scale correlation function of 6dFGS allows the detection of a Baryon Acoustic Oscillation (BAO) signal. The low effective redshift of 6dFGS makes it a competitive and independent alternative to Cepheids and low-z supernovae in constraining the Hubble constant. It also depends on very different systematic uncertainties. We found a Hubble constant of H_0 = 67 +/- 3.2 km/s/Mpc in agreement with analyses of the Cosmic Microwave Background. We also use the measurement of redshift space distortions (f\sigma_8) to test General Relativity. Modifications of General Relativity are one possible explanation of the observed effect of dark energy. My talk will also discuss prediction for the future WALLABY survey, which will be able to constrain f\sigma_8 to 3-4% precision and will provide a low redshift anchor for this sort of measurements. WALLABY is a radio galaxy survey and a precursor for much larger galaxy surveys, which future radio telescopes like the SKA will deliver.
Jan. 27, Friday 12:00 pm (INPA Journal Club)
Amit Yadav, IAS, Princeton
LB 50-5026 (the INPA common room)
"Probing the early universe: primordial non-Gaussianity and gravitational waves"
In first part of my talk I will discuss what we can expect to learn about the dynamics of the universe at the very earliest moments. I will discuss theoretical predictions from inflationary models and their observational consequences. I will focus on two observational signatures which provide complementary information about the physics of the beginning: primordial non-Gaussianity and gravitational waves (CMB B-modes). In second part of my talk I will discuss the current state of CMB polarization information and how various CMB polarization based correlators can be used to extract interesting physics such as patchy reionization, parity violating physics, and primordial magnetism.
Jan 31, Tuesday 1:10 pm
tba,
Hearst Field Annex, B5

December 2011:
Dec. 1, Thursday 12:00 pm
David Marsh, Oxford
LBL 50-5026
"Ultra-light Axions: Degeneracies with Massive Neutrinos and Forecasts for Future Cosmological Observations"
A generic prediction of string theory is the existence of many axion fields. It has recently been argued that many of these fields should be light and, like the well known QCD axion, lead to observable cosmological consequences. In this paper we study in detail the effect of the so-called string axiverse on large scale structure, focusing on the morphology and evolution of density perturbations, anisotropies in the cosmic microwave background and weak gravitational lensing of distant galaxies. We quantify specific effects that will arise from the presence of the axionic fields and highlight possible degeneracies that may arise in the presence of massive neutrinos. We take particular care understanding the different physical effects and scales that come into play. We then forecast how the string axiverse may be constrained and show that with a combination of different observations, it should be possible to detect a fraction of ultralight axions to dark matter of a few percent.
I focus on the lightest axions, with mass < 10^{-28}eV, and present a exact numerical study on their cosmological effects. I will briefly introduce axions in string theory and their motivation as an ultra-light dark matter ingredient based in part on the observance of excess relativistic energy density and neutrino masses. I will then review their known effects on large scale structure, before presenting new work on precision observables and forecasts for a Euclid-style mission. I may also review some other work on an extension of this model to include coupling to other moduli fields. (based upon http://arxiv.org/abs/1110.0502)
Dec. 2, Friday 12:00 pm
Michael Childress, LBL
LBL 50-5026
"Host Galaxies of Type Ia Supernovae from the Nearby Supernova Factory"
Type Ia Supernovae (SNe Ia) are excellent standardizable candles for measuring cosmological distances to map out the expansion history of the Universe, but the precise nature of their stellar progenitors remains unclear. The study of the environments in which SNe Ia are found can yield insight into the nature of their progenitors and provide a critical cross-check on the impartiality of corrected SN Ia luminosities with progenitor properties. Using a sample of SNe Ia and their host galaxies from the Nearby Supernova Factory (SNfactory), we investigate the global properties of SN Ia environments as well as the relationship of SN Ia luminosities to the properties of their host galaxies. We show that the galaxies hosting SNe Ia are extremely normal, and their statistical properties indicate that over two thirds of SNe Ia arise from young (< 500 Myr) progenitors. Hubble residuals of SNfactory SNe Ia show a dependence on the mass, metallicity, and star-formation intensity of their host galaxies, consistent with results of other recent studies. We explore several possible explanations for the origin of this Hubble residual host bias.
Dec. 6, Tuesday 1:10 pm
Fabian Schmidt, Caltech
Hearst Field Annex, B5
"Probing the very early Universe with large-scale structure"
Current and future galaxy surveys will map out a significant portion of the observable Universe. In addition to telling us about what the Universe is made of and how it evolved, the data can be used to probe the origin of the seed perturbations produced during inflation, in particular through primordial non-Gaussianity, and primordial gravitational waves. I will explain the general idea behind both of these and give some concrete examples. I will also discuss some of the theoretical issues that need to be solved in order to realize this potential.
Dec. 7, Wednesday 12:10 pm (Theory Lunch)
Renbin Yan, NYU
Hearst Field Annex, B1
"The Puzzle of LINERs and the Warm Ionized Gas in Early-type Galaxies"
Ever since their discovery, the nature of low ionization nuclear emission-line regions (LINERs) has been hotly debated. Some authors treat them as AGNs, others argue they are not AGNs but powered by shocks or hot old stars. No universal agreement has been reached. On the other hand, early-type galaxies frequently contain spatially extended warm ionized gas and have spectra similar to LINERs. How is this large-scale emission related to the nuclear LINERs? Because LINER-like spectrum is the most common spectral type found in early-type galaxies in both nuclear and integrated spectra, understanding its nature is important to AGN demographics and numerous other topics in astrophysics.
In this talk, you will hear a story of how I converted from a supporter for AGN-powering of LINER line emission to an opponent, and what kind of convincing evidence I find made me convert. I will also discuss what we can learn about the warm ionized gas in early-type galaxies from this line emission, given that it is not an AGN indicator.
Dec. 8, Thursday 4:00 pm (RPM)
Andrew Hearin, Univ. of Pittsburgh
LBL 70A-3377
"Precision Cosmology with Weak Lensing"
Forthcoming projects such as DES, LSST, WFIRST, and Euclid aim to measure weak lensing shear correlations with unprecedented precision, constraining the dark energy equation of state at the percent level and providing precision tests of general relativity. I will address several of the leading challenges to this program. Reliance on photometrically-determined redshifts constitutes a major source of uncertainty for these surveys. Additionally, interpreting the weak lensing signal requires a detailed understanding of the nonlinear physics of gravitational collapse. I will discuss the stringent calibration requirements on these sources of uncertainty, compare these requirements to the contemporary state-of-the-art in predictions of the matter power spectrum and photometric redshift estimation, and discuss strategies to utilize forthcoming data optimally.
Dec. 9, Friday 12:00 pm (INPA Journal Club)
Annalisa Pillepich, Santa Cruz
LBL 50-5026
"Constraining primordial non-Gaussianity with the X-ray eROSITA cluster survey"
According to the standard scenario, the large-scale structure of the Universe that we recognize today under the form of groups and clusters of galaxies, filaments, and sheets is the result of gravitational instability of small density fluctuations generated at very early times. The statistical properties of these seeds are still unclear. The simplest inflationary models produce Gaussian fluctuations but other plausible scenarios give rise to mildly non-Gaussian density perturbations. For the first time, the upcoming generation of cosmic microwave background studies and galaxy and galaxy-cluster surveys should be able to detect signatures of primordial non-Gaussianity. In this talk, I will show how primordial non-Gaussianity affects the statistical properties of the matter distribution at low redshift, thus I will discuss how the abundance and clustering of galaxy groups and clusters from current and future surveys can be used to detect primordial non-Gaussianity. In particular, I analyze the potential of the german/russian X-ray telescope eROSITA, planned to be launched in September 2013, to simultaneously constrain cosmological and X-ray scaling-relation parameters via measurement of the number counts and angular powerspectra of an all-sky photon-count limited sample of galaxy-clusters up to z~1.5.
Dec. 16, Friday 12:00 pm (INPA Journal Club)
Hee-Jong Seo, LBL
LBL 50-5026 (INPA room)
"Acoustic scale from the power spectra of SDSS DR8 photometric luminous galaxies"
We measure the acoustic scale from the angular power spectra of the SDSS III DR8 imaging catalog that includes 872,921 galaxies over ~10,000 deg^2 between 0.45 < z < 0.65. The extensive spectroscopic training set of SDSS III BOSS galaxies allows precise estimates of the true redshift distributions of galaxies in our imaging catalog. Utilizing the redshift distribution information, we build templates and fit to the measured power spectra to derive the BAO scale while marginalizing over enough free parameters to exclude nearly all of the non-BAO information. We derive the ratio of the angular diameter distance to the sound horizon scale at z=0.54; the result is fairly independent of assumptions on the underlying cosmology. We report constraints on cosmological parameters from our measurement in combination with the WMAP7 data and the previous spectroscopic BAO measurements.
November 2011:
Nov. 1, Tuesday 1:10 pm
Dennis Just, Arizona
Hearst Field Annex, B5
"Encounters at the Edge of a Cluster: Environment's Effect on Galaxy Evolution"
While it is well-known that environment influences a galaxy's color, star-formation, and morphology, the exact mechanism is still unknown. For example, the fraction of S0 galaxies in clusters evolves strongly over cosmic time, and has been interpreted as the conversion of spirals into S0s in the cores of clusters. However, I will present evidence that the formation of S0s occurs outside massive clusters, in less dense environments. First, we find that lower-mass systems are responsible for the evolving S0 fraction. Second, we find no signs of recent or ongoing star-formation in the S0s of SG1120, a z~0.4 system of four gravitationally-bound groups that will coalesce into a massive cluster by z=0, placing S0 formation even farther from the cluster environment. Finally, I will highlight a unique spectroscopic survey capable of isolating the infall regions of ~20 clusters from 0.4 < z< 0.8, enabling us to directly explore the environment where the transformation is taking place.
Nov. 4, Friday 12:00 pm (INPA Journal Club)
Johannes Noller, Imperial
LBL 50-5026 (INPA room)
"Emergent galileons and chameleons"
With now Nobel-prize-winning observational evidence for the accelerated expansion of the Universe, we are still in search of a thorough theoretical understanding of its cause. Modified gravity theories such as DGP, galileon and chameleon theories are strong candidates in this enterprise. These models introduce a new scalar degree of freedom in order to modify GR on large scales and generate late-time acceleration. However, this degree of freedom will generically give rise to a new fifth force. In order to comply with tight fifth force constraints on solar system scales, such theories therefore need to come equipped with a screening mechanism that shields the scalar and allows us to recover GR on these scales. I will discuss the connection of these theories with Lovelock gravity and induced metrics as arising in higher dimensional setups. In particular I will show how this allows an exhaustive classification of galileon and chameleon theories, generating new types of such screened theories in the process.
Nov. 7, Monday 12:10 pm (TAC seminar)
Yujin Yang, MPIA
Hearst Field Annex, B5
"Statistics and Kinematics of Lyman-Alpha Blobs"
It is hotly debated whether high-redshift Ly-alpha nebulae (the so-called "Ly-alpha blobs") are sites of intense feedback from star-formation/AGNs or proto-galaxies forming via gas accretion. First, I will present our large-area narrow-band imaging surveys to constrain the clustering and environment of blobs. Ly-alpha blobs show strong field-to-field variation indicating that they occupy the massive dark matter halos (up to ~10^13 Msun), thus will evolve into rich groups or clusters today. Then, I will present a spectroscopic program that targets both Ly-alpha and Halpha lines from the galaxies within Ly-alpha blobs to discriminate between outflowing and inflowing gas models. We measure velocity offsets between Ly-alpha and the Halpha line centers, finding that Ly-alpha peaks are redshifted against Halpha by less than ~250 kms/s. These offsets are small compared to those of normal star-forming galaxies (LBGs), which can be up to ~1000 km/s with an average of +450 km/s. This absence of blueshift of Ly-alpha lines and the small outflow velocities imply that both infall models and extreme "super/hyper"-wind models may not be the source of the extended Ly-alpha emission. Lastly, I will report on dust and molecular properties on the best-studied Ly-alpha blob (Steidel blob 1).
Nov. 7, Monday 2:00 pm (INPA Journal Club, time moved due to TAC talk)
Nico Hamaus, LBNL/Zurich
LBL 50-5026
"Constraining Cosmology with Large-Scale Structure: Optimal Weights and Multiple Tracers"
Large-scale structures carry a wealth of information about the cosmological origin and evolution of the Universe. Galaxy redshift surveys aim at reconstructing these structures, providing a powerful tool to probe the physics of the Cosmos. However, galaxies are biased and stochastic tracers of the dominant dark matter distribution, limiting the attainable accuracy on this reconstruction. A second limitation arises from cosmic variance, which is due to the limited number of Fourier modes that can be observed in a finite volume. I will present a technique to optimize the information content encoded in the statistics of biased tracers of the dark matter density field on the basis of numerical N-body simulations. In concert with a multi-tracer approach to cancel cosmic variance, an optimal weighting scheme to minimize the stochasticity of galaxies is presented and applied to halo catalogs. On the basis of two specific examples, I will illustrate how these methods are applied and what their benefits are.
Nov. 7, Monday 3:10 pm (RAL Seminar cancelled due to illness)
Aaron Parsons, UCB
Hearst Field Annex B5
"A Low-Frequency Radio Astronomy Battle Plan"
Events have been unfolding quickly in the (non-violent) war to conquer the radio sky below 1GHz. Several new projects have taken the field or are advancing rapidly toward funding, particularly in the areas of using 21cm emission to study the pre-reionization dark ages (e.g. LEDA) and baryon acoustic oscillations post-reionization (e.g. BAOBAB). Leading facilities such as GMRT and LOFAR are beginning to crank out new, high-quality observations routinely, while PAPER remains committed to being a focused experiment making an end-run for reionization. The MWA had a headstart, has hit some rough terrain, and yet continues to march forward. Meanwhile, South Africa and Australia are in a final bout to win SKA siting by championing their respective low-frequency progenitors (i.e. PAPER and MWA). HERA and SKA-low await the victors in this battle royale. Who will win? Who will lose? All we know is that the radio sky will never look the same again.
Nov. 8, Tuesday 1:10 pm
Gabor Worseck, Santa Cruz
Hearst Field Annex, B5
"Probing the End of HeII Reionization at z~2.7 with HeII Lyman Alpha Absorption Spectra"
Like hydrogen, intergalactic singly ionized helium can be probed by Lyman alpha forest spectroscopy of quasars. However, the far UV flux of most high-z quasars is extinguished by intervening HI Lyman limit systems. Until recently only a handful of HeII sightlines had been studied in detail with HST. Matching GALEX photometry to quasar catalogs has led to many tens of quasar sightlines that may be clear for the analysis of HeII Lyman alpha absorption. Recently, we detected intergalactic HeII absorption towards 6 UV-bright z~3 quasars with HST/COS. Together with archival sightlines, they enable a systematic investigation of the HeII reionization epoch. The HeII effective optical depth increases from tau~1 at z~2.3 to tau>5 at z~3.2, but with a large scatter of 22.7, indicating that HeII reionization is incomplete. By increasing the redshift path at 2.7 < z < 3 by a factor of four, we, for the first time, probe cosmic variance in the HeII absorption at the end of HeII reionization. Our HST program is complemented by optical spectroscopy of the coeval HI Lyman alpha forest and a deep survey for HeII-reionizing quasars.
Nov. 10, Thursday 12:00 pm (special INPA Journal Club)
Graeme Addison, Oxford
LBL 50B-4205
"Connecting Cosmology and Galaxy Evolution with the Clustering of High-Redshift Dusty Star-Forming Galaxies"
The clustering of high-redshift dusty star-forming galaxies (DSFGs) is currently of interest both as a foreground for Cosmic Microwave Background analysis and for studying galaxy evolution. I will present recent work in which I combine Planck, ACT and BLAST data to construct a simple template for the clustered source contribution to the angular power spectrum, useful for extracting small-scale CMB anisotropy measurements from foreground-dominated maps.
I will then discuss the challenges associated with extracting physical properties (e.g., host halo mass, redshift distribution, dust temperature) of unresolved DSFGs from the angular power spectrum, and how combining different statistics from Planck, Herschel and future data sets can overcome these issues.
Nov. 11, Friday 12:00 pm (INPA Journal Club)
Shahab Joudaki, Irvine
LBL 50-5026
"Beyond the Standard Model of Cosmology: Dark Energy, Neutrinos, and Primordial Non-Gaussianity"
Some of the most outstanding problems of physics lie in the understanding of the dark sector of the universe, in particular dark energy, neutrinos, and inflation. The dark energy and neutrinos are correlated through their effects on distances and the clustering of matter. I will review the present state of surveys sensitive to the effects of dark energy and neutrino mass. I will then forecast how well the present dark energy density and its equation of state along with the sum of neutrino masses may be constrained using multiple probes that are sensitive to the growth of structure and expansion history, in the form of weak lensing tomography, galaxy tomography, supernovae, and the cosmic microwave background. I will include all cross-correlations between these different probes and allow for non-negligible dark energy at early times (motivated by the coincidence problem) in spatially flat and non-flat cosmological models. In the latter portion of the talk, I will discuss a novel method to constrain non-Gaussianity of the primordial density perturbations by its impact on the ionization power spectrum from 21 cm emission during the epoch of reionization. I will show that 21 cm experiments in the near future may constrain inflationary models via primordial non-Gaussianity to the same precision as expected from Planck.
Nov. 15, Tuesday 1:10 pm
Philip Zukin, MIT
Hearst Field Annex, B5
"Self-Similar Secondary Infall: A Physical Model of Galaxy Halo Formation"
N-body simulations have revealed a wealth of information about dark matter halos, but their results are largely empirical. Using analytic means, we attempt to shed light on simulation results by generalizing the self-similar secondary infall model to include tidal torque. Imposing self-similarity allows us to analytically calculate the structure of the the halo in different radial regimes and numerically compute the profiles of the halo without being limited by resolution effects inherent to N-body codes. I will describe this simplified halo formation model and compare our results to mass and velocity profiles from recent N-body simulations. We find that angular momentum plays an important role in determining the structure of the halo at small radii.
Nov. 18, Friday 12:00 pm (INPA Journal Club)
Marilena LoVerde, IAS
LBL 50-5026
"Local Primordial non-Gaussianity in Large-scale Structure"
Primordial non-Gaussianity is among the most promising of few observational tests of physics at the inflationary epoch. At present non-Gaussianity is best constrained by the cosmic microwave background, but in the near term large-scale structure data may be competitive so long as the effects of primordial non-Gaussianity can be modeled through the non-linear process of structure formation. I will discuss recent work modeling effects of a few types of primordial non-Gaussianity on the large-scale halo clustering and the halo mass function. More specifically, I will compare analytic and N-body results for two variants of the curvaton model of inflation: (i) a ``tau_NL" scenario in which the curvaton and inflaton contribute equally to the primordial curvature perturbation and (ii) a ``g_NL'' model where cancellations vanish the usual quadratic f_NL term in the potential, but give rise to a large cubic term.
Nov. 21, Monday 3:45 pm (1/2 hour informal talk in plce of Cadie)
Antonio Dorta, IAA (Spain)
LeConte 4th floor meeting room
"BOSS galaxy population: The evolution of the most massive galaxies in the Universe"
The Baryon Oscillation Spectroscopic Survey (BOSS, Schlegel et al. 2009) is a dark energy experiment designed to measure the baryon acoustic oscillation signal in the large-scale galaxy correlations. By 2014, BOSS will have mapped 1.5 million Luminous Red Galaxies (LRGs) out to z~0.7 over 10,000 square degrees, providing important constraints on the nature of dark matter and dark energy and on the acceleration of the Universe. Such a large galaxy sample will also allow us to track the evolution of the most massive galaxies in the Universe with unprecedented statistics. In this talk I will show preliminary results on some of the main statistical properties that characterize the BOSS CMASS galaxy population, obtained in a sample of about 300,000 galaxies. Photometric stellar masses, mass-to-light ratios and other stellar population properties have been computed using a grid of SPS models with varying SFH, metallicity and dust attenuation, generated with the Flexible Stellar Population Synthesis code (FSPS, Conroy et al. 2009).
Nov. 22, Tuesday 1:10 pm
Laura Book, Caltech
Hearst Field Annex, B5
"Detecting a Gravitational Wave Background with Astrometry"
A stochastic gravitational wave background causes the apparent positions of distant sources to fluctuate, with angular deflections of order the characteristic strain amplitude of the gravitational waves. These fluctuations may be detectable with high precision astrometry, as first suggested by Braginsky et al. in 1990. In this talk I will present our results for the expected statistical properties of such an astrometric signal caused by a stochastic gravitational wave background, as well as the prospects for detecting it using next-generation astrometric surveys.
Nov. 22, Tuesday 3:30 pm (galform)
Freeke van de Voort, Leiden
Hearst Field Annex, B1
"The growth of galaxies and their gaseous haloes"
Gas accretion provides the fuel for star formation, which is inhibited by outflows powered by supernova explosions and active galactic nuclei (AGN). Using cosmological simulations we found that galaxy accretion rates are much lower than halo accretion rates and much more dependent on processes such as metal-line cooling and feedback from star formation and AGN. For massive haloes, the maximum past temperature distribution is bimodal. Cold-mode gas does not experience a shock near the virial radius, whereas hot-mode gas heats up to the virial temperature. Cold-mode gas is therefore much more important for the fuelling of galaxies, and thus for the star formation that follows, than it is for the growth of haloes. Unfortunately there is little direct observational evidence for the predicted cold accretion flows inside haloes. I will show that they are, however, crucial for matching the neutral hydrogen column density distribution, allowing us to conclude that they do not only exist, but have already been detected as Lyman-limit and damped Lyman-alpha systems.
Nov. 29, Tuesday 1:10 pm
Claire Lackner, Princeton
Hearst Field Annex, B5
"Astrophysically Motivated Bulge Disk Decompositions in SDSS"
The division of galaxies into disk and spheroid components is very old and reasonably successful. I will discuss a new set of two-dimensional bulge-disk(B+D) decompositions for 70,000 nearby Sloan Digital Sky Survey (SDSS) galaxies, the largest such set to date. Each galaxy is fit with five different 2-dimensional models and the best fitting model is selected based on chi-squared values and astrophysical constraints (color, bulge-to-total ratio, shape, etc.). Fifty percent of the galaxies cannot be fit with a B+D model, but this represents only 20% of the stellar mass in our sample. Bulge color and shape can be used to separate elliptical-like classical bulges from disk-like pseudo-bulges and this method agrees reasonably well with other methods used to distinguish classical bulges from pseudo-bulges. This large data set can be used to study the properties of different morphological types over a large range of galaxy properties and environments.
October 2011:
Oct. 4, Tuesday 1:10 pm
Robert Feldmann, Fermilab
Hearst Field Annex, B5
"Molecular gas in cosmological simulations"
It has long been known that star formation in the Galaxy takes place within molecular clouds. Only recently, however, have cosmological simulations of galaxy evolution begun to include star formation sub-grid models that are based on the presence of molecular hydrogen. I will present some implications of such an approach. In particular, I will discuss the empirical relations between star formation and molecular gas on (sub-)galactic scales and present a new approach to model the H2-CO conversion factor.
Oct. 6, Thursday 4:10 pm (Astronomy Colloquium)
Risa Wechsler, SLAC/Stanford
3 LeConte
"The Galaxy-Halo Connection Across Mass and Time"
Dark matter halos are the fundamental unit of structure formation and they provide the framework for our modern understanding of galaxyformation. I will discuss new limits on the connection between galaxy properties and their dark matter hosts over a range of masses and redshifts. In the context of a given cosmological model, I will show how the galaxy-halo relation can be tightly constrained at low redshift, and how the galaxy-halo connection can be used to infer the full star formation histories of galaxies. This model, based onLCDM halos, is in excellent agreement with a wide range of data, including the statistics of Magellanic Cloud mass satellites around Milky Way mass hosts. For the faintest dwarfs, there is still considerable degeneracy between the galaxy-halo connection and the properties of dark matter.
Oct. 10, Monday 12:10 pm (TAC seminar)
Michele Fumagalli, Santa Cruz
Hearst Field Annex, B5
"Exploring the gas-cycle in high-redshift galaxies: a joint effort of theory and observations"
Hydrodynamical cosmological simulations indicate that massive galaxies at high redshift are fed by extended streams of cold gas in a smooth component and in merging galaxies. At the same time, observations reveal that winds are ubiquitous in star forming systems. To investigate this balanced cycle of gas in high-redshift galaxies, I will present predictions of the neutral hydrogen distribution and Ly-alpha emission in simulated disks fed by cold-streams. I will then discuss the prospects of mapping the circumgalactic medium with absorption line systems or with imaging and spectroscopy in emission, presenting preliminary results from ongoing programs.
Oct. 11, Tuesday 1:10 pm
Tomer Tal, Yale
Hearst Field Annex, B5
"Minor mergers and the mass growth of massive galaxies"
Massive galaxies in the nearby universe typically have very little cold gas, they host old stellar populations and exhibit extremely low specific star formation rates. Therefore, studies of these galaxies typically find that essentially all of the stellar mass growth takes place through mergers and other gravitational interactions, with the relative importance of each process still debatable. For example, while some authors find that major dry mergers contribute significantly to the mass evolution of massive galaxies, others find only a mild contribution or none at all. Other studies argue that minor mergers and low mass accretion events contribute at least some of the stellar mass growth in massive galaxies over a longer timescale. In this talk I will present results from multiple studies of the contribution of minor mergers to the mass growth of massive galaxies at z<0.7. I will show that essentially all nearby ellipticals have morphological disturbances in their stellar bodies that can be associated with minor merger activity. In addition, I will discuss a purely statistical study of the satellite galaxies around luminous red galaxies in SDSS and show that major mergers are an unlikely contributor to their mass growth. Lastly, I will show that the colors of massive galaxy at extreme radii are consistent with the minor merger growth model.
Oct. 11, Tuesday 3:30 pm
Tucker Jones, Caltech
Hearst Field Annex, B1
"Resolved spectroscopy of gravitationally-lensed galaxies at z=2-3"
The detailed study of high-redshift galaxies is hampered by their small angular sizes and faint apparent magnitudes. Both of these limitations can be overcome by observing gravitationally lensed galaxies, where the apparent size and luminosity are highly magnified by massive clusters. I will present observations of gravitationally lensed z=2-3 galaxies which reveal rotating velocity fields, multiple giant star-forming regions, and steep metallicity gradients with a physical resolution as fine as 100 parsecs. These results suggest that we are witnessing inside-out growth of turbulent rotating galaxies.
Oct. 18, Tuesday 1:10 pm
Ramin Skibba, Arizona
Hearst Field Annex, B5
"Are Brightest Halo Galaxies Central Galaxies?"
It is generally assumed that the central galaxy in a dark matter halo, that is, the galaxy with the lowest specific potential energy, is also the brightest halo galaxy (BHG), and that it resides at rest at the center of the dark matter potential well. This central galaxy paradigm (CGP) is an essential assumption made in various fields of astronomical research. I test the validity of the CGP using a galaxy group catalog constructed from the Sloan Digital Sky Survey, and many mock group catalogs (Skibba et al. 2011). For each group I compute two statistics, R and S, which quantify the offsets of the line-of-sight velocities and projected positions of brightest group galaxies relative to the other group members. By comparing the cumulative distributions of R and S to those obtained from the mock catalogs, I rule out the null-hypothesis that the CGP is correct, and I constrain possible explanations of this, such as central galaxies in motion, and prevalent massive substructures.
Instead, the data indicate that in a non-zero fraction of haloes the BHG is not the central galaxy, but instead, a satellite galaxy. In particular, I find that this fraction increases from 0.25 in low-mass haloes to 0.40 in massive haloes. I show that these values are uncomfortably high compared to predictions from halo occupation statistics and from semi-analytical models of galaxy formation. I end by discussing various implications of these results.
Oct. 20, Thursday 4:10 pm (Astronomy Colloquium)
Fabio Governato, Washington
3 LeConte
"Dark Matter Cores, Bulges and SMBHs: How baryon physics shape the properties of the central regions of galaxies"
How do dark matter cores and bulgeless galaxies form? These common properties of galaxies have been hard to explain within the Cold Dark Matter scenario and have been often referred as the 'core catastrophe' and the angular momentum problem'. I will propose and successfully test a complete physical model based on SNe and Super Massive Black Holes feedback and resulting rapid gas outflows that simultaneously adresses these fundamental problems. I will present results from a new set of cosmological simulations to make predictions on the dark matter and baryon distribution in galaxies over a range of halo masses going from ultra faint dwarfs to spiral galaxies.
Oct. 21, Friday 2:00 pm (INPA Journal Club, time moved due to run-around)
Douglas Watson, Vanderbilt
LBL 50B-4205
"Small scale clustering of galaxies"
In this talk, I focus on using the small-scale clustering of galaxies to study their fate once they have merged into larger systems and become satellites. Specifically, I will focus on two aspects of this work. First, I will discuss recent work that has uncovered a strong luminosity trend of the radial density profile of satellite galaxies, wherein bright satellites are poor tracers of the dominant underlying dark matter, possibly leading to a test of LCDM at the extreme small scales. Second, I will discuss a powerful new technique that uses the spatial clustering of satellite galaxies to understand how their stellar mass loss occurs. Understanding how satellite galaxies can lose stellar mass yield direct predictions for the amount of di#use intrahalo light (IHL) at varying scales, and could prove valuable for providing insight into the physics of galaxy formation. I will present preliminary constraints on stellar mass loss and IHL using clustering measurements from the Sloan Digital Sky Survey.
Oct. 24, Monday 5:00 pm (Segre Lecture)
Blas Cabrera, Stanford
Sibley Auditorium (Bechtel Engineering Center)
"What makes up the dark matter of our universe?"
Through cosmology and particle physics we review our understanding of how our universe came into existence. Of particular interest is what makes up dark matter the source of all structure formation. Direct detection experiments such as CDMS search directly for dark matter particles passing through the laboratory, indirect detection experiments such as GLAST/Fermi look for gamma rays from dark matter particle-antiparticle annihilations, and accelerators such as the LHC at CERN may soon provide direct evidence for the structure of particle physics in dark matter sector.
Oct. 25, Tuesday 1:10 pm
Xiaoying Xu, Arizona
Hearst Field Annex, B5
"A 2% Measurement of the BAO in SDSS DR7 using Reconstruction"
We demonstrate the first application of reconstruction on real observed galaxies in the SDSS DR7 luminous red galaxy catalogue. We also introduce more careful approaches to deriving a suitable covariance matrix and fitting model for galaxy correlation functions. These all aid in obtaining a more accurate measurement of the acoustic scale and its error. We validate our reconstruction, covariance matrix and fitting techniques on 160 mock catalogues derived from the LasDamas simulations in redshift space. We then apply these techniques to the DR7 LRG sample and find that the error on the acoustic scale decreases from ~3.4% before reconstruction to ~1.9% after reconstruction. This 40% reduction in the error is equivalent to the effect of increasing the survey volume by about a factor of 3. We also see an increase by at least 1-sigma in the significance of our BAO detection for 2 different measures of BAO significance.
Oct. 26, Wednesday 12:10 pm (special TAC seminar)
Mariangela Lisanti, Princeton
Hearst Field Annex, B5
"A Flow of Dark Mark Debris: Exploring New Possibilities for Substructure"
Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended ``debris flows'' in the form of shells, sheets, and plumes. I will discuss debris flows in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high-velocity behavior. Unlike tidal streams, which may not intersect the Earth's location, debris flows are spatially uniform and thus guaranteed to be present in the dark matter flux incident on direct detection experiments.
Oct. 27, Thursday 12:00 pm (special INPA seminar)
Jan Kratochvil, Miami
LBL 54-130(Perserverance Hall)
"Probing Cosmology with Weak Lensing Minkowski Functionals and Peak Counts"
In two recent papers we study the cosmological origin of peaks in weak gravitational lensing (WL) convergence maps, and show that Minkowski Functionals (MFs) of WL maps contain significant non-Gaussian, cosmology-dependent information. To do this, we produce a large suite of cosmological ray-tracing N-body simulations to create mock WL convergence maps. For the origin of the peaks, we study which halos in the simulations get pierced by which light rays in the WL maps. For the MF constraints, we study the cosmological information content of MFs derived from these maps. Our suite consists of 80 independent 512^3-particle N-body runs, covering seven different cosmologies, varying three cosmological parameters Omega_m, w, and sigma_8 one at a time, around a fiducial LambdaCDM model. In each cosmology, we use ray-tracing to create a thousand pseudo-independent 12 deg^2 convergence maps, and use these in a Monte Carlo procedure to estimate the joint confidence contours on the above three parameters. We include redshift tomography at three different source redshifts z_s=1, 1.5, 2, explore five different smoothing scales theta_G=1, 2, 3, 5, 10 arcmin, and explicitly compare and combine the MFs with the WL power spectrum. We find that the MFs capture a substantial amount of information from non-Gaussian features of convergence maps, i.e. beyond the power spectrum. The MFs are particularly well suited to break degeneracies and to constrain the dark energy equation of state parameter w (by a factor of ~ three better than from the power spectrum alone). The non-Gaussian information derives partly from the one-point function of the convergence (through V_0, the "area" MF), and partly through non-linear spatial information (through combining different smoothing scales for V_0, and through V_1 and V_2, the boundary length and genus MFs, respectively). In contrast to the power spectrum, the best constraints from the MFs are obtained only when multiple smoothing scales are combined.
Oct. 27, Thursday 4:00 pm (RPM)
Sarah Shandera, Penn State
LBL 50A-5132
"Non-Gaussianity: Testing Inflation through Interactions"
The promise of new, far more precise data from the Planck satellite and from upcoming Large Scale Structure surveys has motivated a fresh perspective on inflation. Near future constraints on non-Gaussianity (higher order statistics) of the primordial fluctuations may allow us to observationally discriminate competing particle physics realizations of inflation or put pressure on the paradigm. I'll review several of the current theoretical ideas and the variety of signals they predict in the CMB and Large Scale Structure.
Oct. 28, Friday 12:00 pm (INPA Journal Club)
Adam Becker, Michigan
LBL 50- 5026
"Constraining Primordial Non-Gaussianity with the CMB and LSS "
Primordial non-Gaussianity provides cosmology one of the precious few connections between primordial physics and the present-day universe. Standard inflationary theory, with a single slowly rolling scalar field, predicts that the spatial distribution of structures in the universe today is very nearly Gaussian random. Departures from Gaussianity, barring contamination from systematic errors or late-time non-Gaussianity due to secondary processes, would be a violation of this standard inflationary assumption. Constraining or detecting primordial non-Gaussianity is therefore an important basic test of the standard cosmological model. Future results from Planck and from large-scale structure surveys will place tight constraints on many of the most popular models of non-Gaussianity. I will discuss several methods used to detect primordial non-Gaussianity, along with projected constraints that will be placed on a simple physically-motivated scale-dependent form of non-Gaussianity from CMB and LSS data in the near (and not-so-near) future.
Oct. 31, Monday 12:00 pm (special INPA seminar)
Arthur Kosowsky, Pittsburgh
LBL 50-5026
"Supernova Peculiar Velocities with LSST and BigBOSS"
The LSST project anticipates detecting 300,000 Type-1a supernovae over 10 years. Since these are standardizable candles, their estimated distance and redshift can be used to estimate peculiar velocities. I will describe how such a velocity catalog can be used to constrain dark energy and modified gravity. The mean pairwise velocity statistic provides notable control over systematic errors. If supernova host galaxy redshifts are measured spectroscopically with BigBOSS, the resulting constraints on the dark energy evolution parameter (w_a) and the growth index parameter (gamma) describing modifications of gravity are among the strongest of any proposed methods.
Oct. 31, Monday 3:10 pm (RAL seminar)
Kathy Kornei, UCLA
Hearst Field Annex, B5
"The Prevalence and Properties of Outflowing Winds at z = 1"
Outflowing winds have been observed in galaxies over a wide range of redshifts and are thought to play an important role in both the quenching of star formation and the enrichment of the intergalactic medium. We present the results of a study at z = 1 tracing the prevalence and properties of outflows in a sample of DEEP2 objects with rest-frame UV spectroscopy and HST optical imaging. We investigate if a critical star formation rate surface density is required to drive outflows, using a new technique for estimating galaxy area based on a physically motivated luminosity threshold. Previous work has suggested that the star-formation rate surface density may be most strongly correlated with outflows (as opposed to the star formation rate); we observe a 3 sigma correlation between outflow velocity (measured from FeII resonance absorption lines) and star-formation rate surface density, compared with only a 1 sigma correlation between velocity and star-formation rate. From HST imaging, we estimate galaxy inclinations and find that outflows are more prevalent in face-on systems. This is consistent with the picture of winds emanating perpendicular to galactic disks. As various interstellar features yield different results about galactic-scale gas kinematics, care must be taken in defining how outflows are measured. Specifically, the kinematics of MgII absorption often suggest stronger blueshifts than those measured from FeII absorption lines. By conducting analyses on a per-object basis at z = 1, we are able to examine the relationship between outflow properties and individual galaxy morphology, stellar populations, and star formation surface density, at the epoch when the global star-formation rate is beginning its decline to the present day.
September 2011:
Sep. 1, Thursday 4:00 pm (RPM)
David Schlegel, LBNL
LBL 50A-5132
"BOSS, BigBOSS, and Beyond"
Sep. 2, Friday 12:00 pm (INPA Journal Club)
Teppei Okumura, IEU, Institute for the Early Universe
LBL 50B-4205 (Note Room change)
"Distribution function approach to redshift space distortions: N-body simulations"
Galaxy redshift surveys are one of the most powerful tools to probe cosmological models. Particularly measurement of redshift space distortions (RSD), caused by peculiar velocities of galaxies, offers an attractive method to directly probe the cosmic growth history of density perturbations. A distribution function approach where RSD can be written as a sum over density weighted velocity moment correlators has recently been developed. In this talk I present the redshift-space power spectrum based on this approach using N-body simulations and show that this formalism predicts the true power spectrum up to sufficiently small scales. Although I focus only on the dark matter clustering, the analysis presented here can be naturally extended to biased objects such as dark matter halos and galaxies.
Sep. 6, Tuesday 1:10 pm
Bennny Trakhtenbrot, Tel Aviv
Hearst Field Annex, B5
"Observing the Growth of the Most Massive Black Holes at High Redshifts"
There is ample evidence that the most significant growth epoch of the majority of super-massive black holes (SMBHs) must have occurred at z>1-2. I will present our team's efforts to measure black hole masses and accretion rates in several high-redshift samples of AGNs, based on extensive NIR spectroscopic campaigns. I will particularly focus on a large sample of z~5 AGNs, which were observed in a combined VLT/Gemini campaign. This sample probes the most massive BHs at this epoch, but shows lower masses and higher accretion rates than those of z~2-3.5 sources. When combining these samples together, a clear evolutionary sequence is evident: the z~5 BHs grow through Eddington-limited accretion from a broad range of seed masses; their subsequent growth, at duty cycles of ~10-20%, forms the most massive BHs observed at z~2. I will also mention a few follow-up campaigns which aim at understanding the co-evolution of these BHs with their host galaxies.
Sep. 9, Friday 12:00 pm (INPA Journal Club)
Sudeep Das, Berkeley/BCCP/LBL
LBL 50B-4205 (Note Room change)
"A New view of the CMB from the Atacama Cosmology Telescope"
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 and possible deviations from the Standard Model, they will also be unique in a new way - they will allow us to measure the gravitational lensing of the CMB. This lensing is 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 AC T. In the second part, I will discuss the scientific potential of the CMB lensing signal, its first detection, a new way to constrain dark energy, and its prospects for cross-correlation with other datasets. Finally, I will discuss the upcoming polarized counterpart of ACT --- the ACTPol project, which will have greater sensitivity 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.
Sep. 13, Tuesday 1:10 pm
Mustafa Amin, MIT
Hearst Field Annex, B5 (also videoconferenced to LBL 50A-5131 if possible)
"Quintessential acceleration and its end"
What if dark energy undergoes a phase transition in the late universe? What are the observational implications, what set of observations could constrain such a transition. In this talk, I will discuss the observational consequences of the quintessence field rolling to and oscillating near a minimum in its potential, "if" it happens close to the present epoch (z<0.2). I will show that in a class of models, the oscillations lead to a rapid growth of the field fluctuations and the gravitational potential on subhorizon scales. The growth in the gravitational potential occurs on timescales << H^(-1). This effect is present even when the quintessence parameters are chosen to reproduce an expansion history consistent with observations. For linearized fluctuations, I will show that although the gravitational potential power spectrum is enhanced in a scale-dependent manner, the shape of the dark matter/galaxy power spectrum is not significantly affected. The best constraints on such a transition in the quintessence field is provided via the integrated Sachs-Wolfe (ISW) effect in the CMB temperature power spectrum. Going beyond the linearized regime, the quintessence field can fragment into large, localized, long lived excitations with sizes comparable to galaxy clusters (or smaller); this fragmentation could provide additional observational constraints.
Two quoted ``signatures" of modified gravity are a scale-dependent growth of the gravitational potential and a difference between the matter power spectrum inferred from measurements of lensing and galaxy clustering. Here, both effects are achieved by a minimally coupled scalar field in general relativity with a canonical kinetic term.
If time permits, I will talk about similar phenomenon in the early universe (at the end of inflation). In that scenario, the transition is theoretically well motivated and necessary, but the details are harder to constrain observationally.
Sep. 16, Friday 12:00 pm (INPA Journal Club)
Eli Rykoff, LBNL
LBL 50B-4205
"Cosmology With Optically Selected Galaxy Clusters: Looking Forward to DES"
In the next few years, large scale optical surveys such as DES will detect galaxy clusters as high as z~1 over several thousand square degrees. In conjunction with stacked weak-lensing calibration, DES optical clusters will be used to place tight constraints on cosmological parameters, extending successful work at low redshift with SDSS data. Unfortunately, cluster mass is not a direct observable, and we must rely on other quantities that trace mass. Optical richness based on multi-band photometric data is one such mass proxy, although it may suffer from large scatter in the mass-richness relation. Minimizing this scatter, and understanding the covariance among the various cluster observables, is necessary to achieve our goals of precision cosmology. To this end, we have made use of the wealth of data available for galaxy clusters by combining large samples of clusters with weak-lensing data and X-ray photon maps to develop an optimized matched filter richness estimator that minimizes mass-richness scatter. This richness estimator forms the basis of redMaPPer, a new red sequence optical cluster finder for use on multi-band photometric data such as DES. Extensive testing on both simulated mock DES catalogs and real SDSS data have shown that we achieve very precise redshift calibration, and testing on the mocks have shown high purity and completeness as well as low mass scatter up to z~1.0. By leveraging faint red cluster members we can also calibrate photometric redshifts for red galaxies to much fainter magnitudes than is typically possible with spectroscopic samples, improving large-scale structure constraints available from photometric data.
Sep. 19, Monday 12:10 pm (TAC seminar)
Laura Blecha, Harvard
Hearst Field Annex, B5
"Connecting Double-peaked Narrow-Line AGN and Dual SMBHs in Galaxy Merger Simulations"
Supermassive black hole (SMBH) pairs must be common through the history of the Universe, according to the hierarchical-growth paradigm. Nonetheless, until recently only a few resolved pairs were known. Recent spectroscopic surveys have greatly increased the number of candidate dual SMBHs, finding that about 1% of active galactic nuclei (AGN) have double-peaked narrow [OIII] lines, which may arise from SMBH orbital motion on kiloparsec scales. Follow-up imaging reveals strong evidence that some of these are in fact dual SMBHs. On the theoretical side, however, little has been done to understand the nature of double-peaked narrow-line (NL) AGN. I will describe a first attempt to model the NL region using hydrodynamic simulations of galaxy mergers. We use a semianalytic prescription for the narrow H-beta emission, from which we can construct line profiles at each stage of the merger and examine the origin of double-peaked features. We find that double-peaked NLs induced by BH motion are a fairly generic but short-lived feature of major mergers, indicating that most comparable-mass dual SMBHs should pass through this phase, if only briefly. Double-peaked spectral features that arise from gas kinematics also occur throughout the galaxy merger but are most common at late stages, during the kpc-scale phase or soon after the BH merger. We additionally explore the dependence of double-peaked NL activity on merging galaxy parameters such as mass ratio and gas content, in the context of determining which mergers are most likely to produce observable double-peaked NLs.
Sep. 20, Tuesday 1:10 pm
Peter Behroozi, Stanford/SLAC
Hearst Field Annex, B5
"Constraining the Complete Star Formation History of Observable Galaxies from z=0 to z=8"
We present a comprehensive approach for deriving the star formation history of the universe self-consistently with a wide array of observations (stellar mass functions, stellar mass clustering, specific star formation rates, and the cosmic star formation rate) and with merger rates from N-body simulations in the context of LCDM cosmology. Our approach explores a wide parameter space of systematic uncertainties, allowing a broader range of possible star formation scenarios at high redshifts; these uncertainties include aspects (e.g., a steeper faint-end slope for the stellar mass function) which help resolve tensions between the cosmic star formation rate and stellar mass functions for LBGs at z>1. We present derived constraints on the star formation rates and histories for galaxies as a function of stellar and halo mass from z=0 to z=8. We show that constraints from observations favor a clear change in the star formation rates of massive galaxies around z=2, consistent with a transition from cold-mode to hot-mode accretion at that redshift and very old stellar populations at the present day. We find, on the other hand, that low-mass galaxies do not have a similar break and that many have star formation histories which have been increasing ever since the galaxies first formed. We also discuss the largest uncertainties on current constraints and the direction that future surveys should take to best increase our understanding. In summary, we provide for the first time a complete, consistent picture of the evolutionary path of galaxies over 96% of the history of the universe, with profound implications for galaxy simulations, semi-analytic models, and our understanding of star formation in the cosmos.
Sep. 23, Friday 12:00 pm (INPA Journal Club)
Beth Reid, LBNL
LBL 50B-4205
"Towards a model of redshift space distortions worthy of BOSS data"
Interest in using redshift space distortions (RSD) as a precise test of General Relativity on large scales has exploded in the last few years, but our theoretical models must be improved to match the statistical precision of current data. In this talk I will review of physics of redshift space distortions in configuration space and present projections for RSD constraints from the BOSS survey. While many recent studies focus on understanding dark matter clustering in redshift space, galaxies occupy special places in the universe: dark matter halos. Our model reproduces the complex dependence of redshift space clustering on halo bias seen in N-body simulations and is sufficiently precise to model the final BOSS data set on scales of r >~ 25 Mpc/h. A better treatment of 'fingers-of-god' from satellite galaxies is still needed to maximize the cosmological information available from RSD on these large scales.
Sep. 26, Monday 4:30 pm (Physics Colloquium)
Juan Collar, Chicago
1 LeConte Hall
"Certainty and uncertainty in dark matter searches"
Departing from the context of CoGeNT and COUPP, two direct searches for WIMP dark matter, we will inspect the recent landscape of anomalies observed by these and several other detectors. The aim of this talk is to communicate an appreciation for the subtleties inherent to experimental efforts in this field, and for the considerable difficulties that await for those trying to make sense of WIMP search observations (or lack thereof).
Sep. 27, Tuesday 1:10 pm
Erik Tollerud, Irvine
Hearst Field Annex, B5 (also videoconferenced to LBL 50A-5131 if possible)
"Local Dwarf Galaxies and LCDM Near-Field Cosmology"
Dwarf galaxies are a frontier for new discoveries in both galaxy formation and cosmology. I discuss work centered around connecting LCDM and its predictions to observations of dwarf galaxies at three different scales of "dwarf". I will discuss the Milky Way's satellites and both solutions and lingering troubles with their abundances and scalings. The strangest of these puzzles manifest in the bright dSphs, which seem to be under-dense relative to LCDM expectations. With this in mind, I present results from a large spectroscopic survey of M31's dSph satellites searching for signs of similar puzzles. These reveal consistency between the Milky Way and M31 satellite populations, showing these puzzles are not unique to the Milky Way. Finally, I will describe a search for bright satellites (analogous to the LMC) in the SDSS, and compare their abundances and properties to straightforward LCDM expectations. These reveal an amazing level of consistency between the SDSS and LCDM for bright satellites. Interpreting these galaxies in this LCDM context provides some interesting new questions regarding satellite quenching and the red-blue sequence bimodality. Taken together, these results suggest that there is a particular scale in galaxy formation at Vc~50 km/s, at which either LCDM begins to break down or galaxy formation becomes overwhelmingly stochastic.
Sep. 30, Friday 12:00 pm (INPA Journal Club)
Teruyuki Enoto, Stanford
LBL 50B-4205

August 2011:
Aug. 12, Friday 12:00 pm (INPA journal club)
Tristan Smith, UC Berkeley
LBL 50-5026
"Beyond the the standard cosmological model: neutrinos and non-Gaussianity"
The cosmic microwave background (CMB) has provided us the laboratory in which we entered the era of 'precision cosmology'. By and large these observations have confirmed the basic, standard, cosmological model which supposes a universe seeded with Gaussian initial fluctuations and filled with non-relativistic matter, photons, and 3 neutrino species. As observations have become more accurate it has become increasingly pertinent to test some of the assumptions that have gone into building the standard cosmological model. In this talk I will present some of my recent work on testing these assumptions.
First I will discuss how recent measurements of the small-scale CMB have hinted at the presence of extra relativistic energy density within the universe. Any interpretation of these results will necessitate the measurement of some of the properties of any extra relativistic energy density. Using recent small-scale measurements of the CMB, along with my colleagues, I have been able to constrain the clustering properties of the extra relativistic energy density. We show that current observations disfavor the interpretation that any extra relativistic energy consists of standard neutrinos.
Second, there has been an increasing interest in testing whether the initial fluctuations follow Gaussian statistics. These tests of 'primordial non-Gaussianity' use estimators constructed from either the CMB three-point (bispectrum) or four-point (trispectrum) correlation functions. Usually an estimator constructed from data is assumed to have a Gaussian probability distribution (PDF) as a result of the central limit theorem. However, in this case the central limit theorem does not apply since the number of terms that appear in these estimators are much greater than the number of measurements. A complete knowledge of the shape of the PDF is necessary in order to properly assign confidence limits to any constraint. I will discuss how Monte Carlo simulations show that the PDF for these estimators are highly non-Gaussian themselves, necessitating more care in using these estimators, especially for future observations with the Planck satellite. I will also show how the constraining power of these estimators may be improved by using a realization-dependent normalization.
Aug. 18, Thursday 12:00 pm (special cosmology seminar)
Jean Coupon, Tohoku University
LBL: Perserverance Hall Annex
"New insights on galaxy evolution since z ~ 1.2 from the CFHT Legacy Survey"
In the last few years, it is has become increasingly apparent that the mass of dark matter haloes in which galaxies reside is a key factor in regulating their formation and evolution. It is now evident that galaxies in low- and high-mass haloes experience very distinct fate. In this presentation, I will first explain why studying the relationship between stellar mass and halo mass brings valuable clues about physical processes involved in galaxy evolution. In the context of the halo model, the simple - but powerful - assumption that the number of galaxies only depends on halo mass, the halo occupation distribution (HOD) model, leads to an accurate analytic prediction of the galaxy distribution. Reciprocally, interpreting galaxy clustering using the HOD model allows to make a direct comparison between galaxy properties and halo mass. By using accurate galaxy clustering measurements over 133 deg2 of the "Wide" component of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS), we performed a detailed investigation of the changing relationship between galaxies and the dark matter haloes they inhabit from z ~ 1.2. I will then pursue my talk with a presentation of this unique data set combining depth, large area and high image quality, and I will finally present our results and their implications for galaxy evolution.
Aug. 23, Tuesday 2:10 pm
Andreas Burkert, Munich
Hearst Field Annex, B1
"The Physics of Self-Regulated Star Formation"
Star formation, despite its importance, is not well understood up to now. Galaxies, like the Milky Way contain large quantities of cold, dense molecular gas that should collapse gravitationally and burst into stars on a timescale of order a few million years. As a result, galaxies should be burned out by now which is in contrast to observations.
At the moment the physics of the interstellar medium and star formation is still in an early phase of exploration. This situation is however changing quickly. High-resolution observations provide detailed insight into the complex structure of the turbulent interstellar medium and its various gas phases. The star formation history of molecular cloud regions like Taurus and Orion has been investigated in great details. At the same time, numerical simulations have achieved enough resolution and complexity in order to explore the origin and evolution of turbulent molecular clouds and their fragmentation into stars and stellar clusters within the dynamical galactic environment.
I will first summarize some of the most puzzling and challenging questions of star formation and then discuss a powerful new approach that links star formation in galaxies to their cosmic baryonic accretion history. I then will present new numerical simulations by Dobbs et al. (2011a,b) on the evolution of the molecular web in disk galaxies that provide new insight into the self-regulated evolution of the multi-phase interstellar medium and its condensation into stars.
Aug. 25, Thursday 4:00 pm (RPM)
Joe Silk, Oxford/JHU
LBL 50A-5132
"Do We Understand How Galaxies Formed?"
Aug. 30, Tuesday 1:10 pm
Adrian Liu, MIT
Hearst Field Annex, B5
"From theoretical promise to observational reality: calibration and foreground subtraction in 21cm tomography"
By using the redshifted hyperfine transition to map out the cosmic distribution of neutral hydrogen, 21cm tomography has the potential to probe the Epoch of Reionization, the preceding Dark Ages, and fundamental physics at unprecedented levels of accuracy. Realizing this theoretical promise, however, will be challenging given that the cosmological signal is expected to be on the order of ~10mK, whereas contaminating foregrounds such as Galactic synchrotron radiation are expected to be ~100 to 1000K. A successful experimental effort with thus require an exquisitely well-calibrated radio interferometer array, as well as data processing algorithms that are capable of high precision foreground subtraction.
In this talk, I will first review existing proposals for 21cm calibration and foreground subtraction. I will then discuss the key differences between 21cm tomography, traditional radio astronomy, and other cosmological probes such as the cosmic microwave background and galaxy surveys. Understanding these differences naturally leads to our proposals for redundant calibration, principal component models of foreground spectra, and a systematic, unbiased framework for foreground subtraction. Utilizing all these tools, our recent work suggests that despite its challenges, turning 21cm tomography into an observational reality is an achievable goal, paving the way for a new understanding of both astrophysics and cosmology.

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.

Cosmology Seminars in Previous Years

   
            
 
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