Upcoming and Previous Seminars (Past months or Previous years)

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

Physics/Astronomy C290C Cosmology and Cosmology-BCCP Seminar
The Physics/Astronomy C290C series consists of the Cosmology-BCCP LBNL-Physics-Astronomy Cosmology seminars held Tuesdays 1:10-2:00 pm in room B1 (also videoconferenced to 50-5026) Hearst Field Annex. 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:

Aug 2013:
Sep 2013:
Sep 17, Tuesday 1:10 pm (Cosmology-BCCP)
Matthias Steinmetz, Potsdam
Hearst Field Annex, B1 (also videoconferenced to 50-5026)

Past Months

Previous years)
May 2013:
May 7, Tuesday 1:10 pm (Cosmology-BCCP)
Eric Bell, Michigan
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"The effects and importance of galaxy merging in a cosmological context"
Mergers between dark matter halos, and the galaxies in them, are a central feature of Lambda CDM. In this talk, I explore the role of galaxy merging in setting the properties of galaxies, in particular the properties of non-star forming (quiescent) early-type galaxies. I will discuss a number of relevant considerations : the observation that the best structural predictor of quiescence is light profile shape (i.e., relative size of the bulge); the comparison between inferred merger rates and the rate of creation of early-type galaxies; the effect of merging on setting the scaling relations of present-day early-type galaxies, and the result that < ~10% of cosmic-averaged star formation is directly triggered by mergers. I will argue that mergers are a crucial part of how early-type galaxies come into place. I will conclude with a number of potentially important open issues: the frequent existence of disks and/or rotation in early-type galaxies, controversies about the amount of evolution in stellar mass and size in the most massive early-type galaxies, the ever-open issue of the feedback mechanism that actually keeps cold gas out of galaxies, and thoughts about the importance of galaxy merging at small galaxy masses.
May 9, Thursday 4:00 pm (RPM)
Antony Lewis, Sussex
LBL 50A-5132
"Cosmological Parameters from Planck and Constraints and Neutrino Physics"
I will briefly review results from the first Planck data release, and explain how they can be used to measure various cosmological parameters. I'll describe the problems of model dependence and degeneracies, and then focus on what the data can tell us about neutrino physics: constraints on both total energy density and mass, and constraints on the properties of massive sterile neutrinos.

April 2013:
Apr 2, Tuesday 1:10 pm (Cosmology-BCCP)
Daniel Stark, Arizona
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Early Star Forming Galaxies and Cosmic Reionization"
Deep infrared images from the Hubble and Spitzer Space Telescopes have pushed the cosmic frontier back to just 500 million years after the Big Bang, delivering the first reliable census of galaxies in what is likely the heart of the reionization era. I will discuss implications of these results for the growth of early galaxies and their contribution to reionization. I will then present the latest results of a large spectroscopic program aimed at using galaxies as probes of the progress of reionization. Finally, I will discuss how spectroscopic study of gravitationally-lensed galaxies is yielding insight into the likely escape fraction and ionizing output of galaxies in the reionization era while simultaneously helping to define a new method of spectroscopically studying galaxies at z>7.
Apr 3, Wednesday 3:00 pm (special talk)
Douglas Finkbeiner, Harvard
325 LeConte Hall
Looking for WIMPs in all the right places: Fermi and the 135 GeV line"
The nature of dark matter is one of the great mysteries of physics. Both direct and astrophysical searches for weakly interacting massive particle (WIMP) dark matter have yielded tantalizing results in recent years, including hints of a gamma-ray line in the inner Milky Way at 135 GeV in Fermi LAT data. There is no process in Standard Model physics that can produce such a line, but some WIMP models could. If the line is confirmed by additional data, it would have a far-reaching impact on particle physics and cosmology. I will summarize the current state of the observations of the Galactic center, clusters, and unassociated halo objects, and speculate about models of particle dark matter that could explain the data.
Apr 4, Thursday 4:00 pm (RPM)
Douglas Finkbeiner, Harvard
LBL 50A-5132
"Looking for WIMPs in all the right places: Fermi and the 135 GeV line"
The nature of dark matter is one of the great mysteries of physics. Both direct and astrophysical searches for weakly interacting massive particle (WIMP) dark matter have yielded tantalizing results in recent years, including hints of a gamma-ray line in the inner Milky Way at 135 GeV in Fermi LAT data. There is no process in Standard Model physics that can produce such a line, but some WIMP models could. If the line is confirmed by additional data, it would have a far-reaching impact on particle physics and cosmology. I will summarize the current state of the observations of the Galactic center, clusters, and unassociated halo objects, and speculate about models of particle dark matter that could explain the data.
Apr 9, Tuesday 1:10 pm (Cosmology-BCCP)
Nicola Mehrtens, Texas A & M
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"The XMM Cluster Survey (XCS): results from the first data release"
The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM-Newton Science Archive. Its main aims are to measure cosmological parameters, trace the evolution of X-ray scaling relations, and investigate galaxy evolution in the densest environments. In this talk I will present the X-ray and optical methodology used to construct the XCS first data release (XCS-DR1); a catalog of 503 galaxy clusters of which 401 have measured X-ray temperatures. I will then feature some results derived from this catalog, highlighting investigations into the evolution of the X-ray luminosity--X-ray temperature scaling relation, the impact of AGN feedback on the intracluster gas, and the halo occupation of BOSS galaxies within XCS clusters.
Apr 12, Friday 12:00 pm (INPA talk)
Ofer Lahav, UCL
LBL Bldg. 50, room 5026 (the INPA common room)
"The Dark Energy Survey"
Apr 16, Tuesday 1:10 pm (Cosmology-BCCP)
no talk--BCCP meeting rest of week,
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
Apr 17-20, Wed-Sat
Cosmology Beyond The Power Spectrum
(Meeting, BCCP)

Apr 23, Tuesday 1:10 pm (Cosmology-BCCP)
Paul Martini, OSU
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"The Mystery of Dust in Early-Type Galaxies"
Approximately half of all early-type galaxies are observed to have dust, yet the origin of this dust remains a mystery. Two origins have been proposed to explain the dust: creation in the stellar winds of their evolved stellar populations and the accretion of dusty satellites, yet neither appears to be completely successful. In order to resolve this issue, I have fit dust models and estimated dust masses (or established upper limits) for a representative sample of early-type galaxies with mid- to far-IR photometry. I will present a demographic analysis of the dust mass distribution in these galaxies and combine estimates of the expected rate of internal production, the rate of dusty satellite accretion, and the dust destruction timescale to explain the origin of the dust.
Apr 23, Tuesday 4:00 pm (RPM)
Jon Sievers, Princeton
LBL 50A-5132
"Cosmology at 17,000 Feet: Results from the Atacama Cosmology Telescope"
The Atacama Cosmology Telescope (ACT) is a 6-meter diameter telescope observing the Cosmic Microwave Background (CMB) high in the Chilean Andes. ACT observed the intensity of the CMB from 2007-2010, and is about to begin polarization observations. We present results from the full ACT intensity-only dataset, such as the first direct detection of the motion of galaxy clusters through the kinematic Sunyaev-Zeldovich effect and the first detection of the lensing of the CMB through its signature on the 4-point function. We also combine ACT data with results from other CMB experiments (Planck,WMAP, South Pole Telescope) and complementary cosmological data such as measurements of the Hubble Constant and baryon acoustic oscillations.
Apr 26, Friday 2:00 pm (INPA talk-special time)
Alberto Vallinotto, UCB
LBL Bldg. 50, room 5026 (the INPA common room)
"Cosmic Team Play: how cross-correlations can help a more comprehensive understanding of the universe"
Cosmological observations are taking great strides toward a better characterization of the observable universe. In this talk I show how several different cosmological observables are correlated with one another, sometimes in unexpected ways. I will then argue that including cross-correlation information can help in tightening constraints on cosmological parameters. As examples, I will consider the effect of weak lensing on the measurement of Type Ia supernovae, the cross-correlation of CMB lensing with the Lyman-a forest (and the constraints that it can potentially yield on the sum of the neutrino masses) and the cross-correlation of CMB lensing with photometric galaxy and weak lensing survey.
Apr 30, Tuesday 1:10 pm (Cosmology-BCCP)
Chris Kochanek, OSU
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"The Structure of Quasar Emission Regions"
In a gravitationally lensed quasar, stars in the lens galaxy produce a time varying magnification of each lensed image whose amplitude is regulated by the size of the emission region. Using this ``gravitational microlensing'' we can now measure the sizes of accretion disks as a function of wavelength and black hole mass, as well as the sizes of the non-thermal X-ray and line emission regions. While the size of the disk appears to scale with black hole mass as expected from thin disk theory, the absolute size is several times larger than predicted. The X-ray emission is produced very close to the inner disk edge and the line emission region sizes are consistent with those measure by reverberation mapping.
Apr 29, Monday 12:10 pm (TAC)
Ben Oppenheimer, Leiden
Hearst Field Annex, B5
"Deviations from a Uniform Meta-Galactic Ionization Background: Implications for Galaxy Formation"
I will first motivate three reasons why metals in diffuse phases, the intergalactic and circumgalactic media, are important for problems in galaxy formation. The first poses the key test as to whether we can match the observed metal census across all phases, including the halos of galaxies, with the theoretical amount of metals produced from stellar nucleosynthesis. The second reason emphasizes how metals change the cooling dynamics of circumgalactic gas, altering processes of accretion and star formation that determine the stellar assembly histories of galaxies. Finally, quasar metal absorption lines at z>2 can trace signatures of early dwarf galaxies, perhaps even those responsible for reionization, which cannot be observed directly via stellar light since they are too faint. A uniform meta-galactic ionizing background is usually assumed in these studies to translate the observed metal absorption columns into the underlying physical properties of gas outside galaxies. I will argue this could be a dramatically bad assumption for metals, because AGN provide ionizing flux above the level of the standard ionizing background. Of course it is well-known that quasars ionize local proximity zones, but what I will emphasize is the stage that follows when the quasar turns off and metals remain out-of-equilibrium. Quasar proximity zone fossils, where metals are over-ionized for timescales exceeding the AGN lifetime could affect a significant fraction of diffuse metals and change the standard assumptions about the gas that typical metal absorbers trace. I will argue our proximity zone model can reproduce key observations of a metal absorber at z=0.9 with both Ne VIII and Mg II.

March 2013:
Mar 5, Tuesday 1:10 pm (Cosmology-BCCP and also AO--joint seminar)
Chris Fassnacht, Davis
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Taking a sharp look at galaxies and gravitational lenses"
The investigation of small-scale structure in galaxy halos and the determination of cosmological parameters benefit greatly from the combination of sensitive imaging and high angular resolution. In this talk I will show how Keck adaptive optics observations of strong gravitational lens systems (those in which multiple images of the background object are formed) can give us insight into these areas. For objects that are red, either because they are at high redshift or because they are dusty, I will demonstrate that the Keck AO imaging is of higher quality than HST observations of the same objects. I will show how the combination of lensing and high-resolution imaging has led to the detection of effectively dark substructure in galaxy halos and can be used to place competitive constraints on dark energy parameters.
Mar 8, Friday 2:10 pm
Julio Navarro, Victoria
"Dwarf Galaxies as Cosmological Probes"
A prime challenge to our understanding of galaxy formation concerns the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in the current #CDM paradigm. This is usually accounted for by assuming that energetic feedback from evolving stars confines dwarf galaxy formation to relatively massive halos spanning a narrow mass range. I will highlight a number of observations that may be used to test this assumption and discuss the puzzles and challenges that arise from this analysis.
Mar 11, Monday 12:10 pm (TAC)
Lars Hernquist, Harvard
Hearst Field Annex, B5
"Cosmology on a Moving Mesh"
Understanding the formation and evolution of galaxies in a cosmological context using numerical simulations remains an elusive goal. In this talk, I describe a new approach to modeling the hydrodynamics of galaxy formation in which the equations of motion are solved on a moving mesh. The use of a moving mesh makes the scheme fully Lagrangian, unlike popular particle-based codes which are quasi-Lagrangian in nature, and mitigates against advection errors when a spatially fixed grid is used. I present results from an initial study comparing results for a moving mesh with those obtained using a smoothed particle hydrodynamics solver. This preliminary work suggests that the new approach offers promise for resolving the long-standing problems which have plagued this field for nearly two decades.
Mar 12, Tuesday 1:10 pm (Cosmology-BCCP)
Raul Angulo, SLAC/Stanford
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Successes and limitations of Cosmological N-body simulations"
In this talk I will discuss recent advances in simulating the spatial distribution and properties of galaxies in the Universe. Firstly, I will show how numerical simulations will help us to understand and exploit the precise measurements of upcoming galaxy surveys. As an example of this, I will discuss the predicted distortions in the baryonic acoustic oscillation signal when it is measured in the galaxy distribution. In the second part of my talk, I will discuss the limitations of N-body simulations and how some physical results might be hidden due to numerical artifacts. As an example of this, I will discuss the case of Warm Dark Matter cosmologies and I will present a possible solution to these problems.
Mar 18, Monday 3 pm (special talk)
Jeffrey Filippini, Caltech
325 LeConte
"Casting a cold eye on the dark universe"
Decades of work by countless astrophysicists have built a quantitative understanding of the composition, history, and fundamental laws of our cosmos. Despite these successes major mysteries remain, among them the nature of the dark matter that forms the foundation of cosmic structure and the physics behind the inflationary epoch that begins our story of the universe. These and other mysteries suggest new fundamental physics waiting to be discovered. I will describe two efforts to probe such fundamental mysteries with novel instrumentation. The first is the quest to directly detect the interactions of dark matter in detectors deep beneath the earth's surface, in particular those of the Cryogenic Dark Matter Search (CDMS). The second is a suite of instruments to observe the imprint of cosmic inflation on the polarization of the cosmic microwave background from vantage points on (BICEP2, Keck) and far above (SPIDER) the Antarctic ice. Each of these instruments employs novel sub-Kelvin instrumentation to achieve the exquisite sensitivity and control of systematic errors needed to push forward the frontiers of these endeavors. I will discuss the status of these instruments and what the future of these programs may hold.
Mar 19, Tuesday 1:10 pm (Cosmology-BCCP)
Eduardo Rozo, SLAC/Stanford
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Ushering in DES Cluster Cosmology with redMaPPer"
We briefly review the current state of cluster cosmology, placing particular attention to the recent claims of 3sigma evidence for non-zero neutrino mass in the literature. Following this review, we will introduce redMaPPer, a new cluster finding algorithm specifically optimized for use in large photometric surveys like the Dark Energy Survey and the Large Synoptic Survey Telescope. We evaluate its performance by applying it to the SDSS data set, and discuss some of the exciting science question that redMaPPer clusters will enable to ask within DES.
Mar 21, Thursday 4:10 pm (Astronomy Colloquium)
Jason Prochaska, Santa Cruz
1 Le Conte
"Quasars Probing Quasars: Insights into Massive z~2 Galaxies"
I will discuss the Quasars Probing Quasars survey which is a spectroscopic campaign of close, z>2 quasar pairs discovered in SDSS, BOSS, and dedicated follow-up programs. Emphasis of this talk will be on using these pairs to study the circumgalactic medium (CGM) of the massive z~2 galaxies "tagged" by an active quasar. The results constrain the processes of inflow and outflow onto these massive galaxies, formation scenarios for the intragroup medium, and models for the radiative emission (and feedback effects) of bright AGN.
Mar 26, Tuesday spring break
Mar 26, Tuesday 4:00 pm (RPM)
Martin White, UCB/LBL
Building 50 Auditorium
Planck (audio plus slides here and there is also 432 Mb mp4 here)
The European Space Agency's Planck satellite was launched on 14 May 2009, and has been surveying the sky stably and continuously since 13 August 2009. In March of 2013, ESA and the Planck Collaboration released to the public a first complete set of data products. I will review some of the highlights of this release for cosmology and early Universe physics.

February 2013:
Feb 5, Tuesday 1:10 pm (Cosmology-BCCP)
Enrico Pajer, IAS
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"The Effective Field Theory of Large Scale Structures"
An analytical understanding of large-scale matter inhomogeneities is an important cornerstone of our cosmological model an helps us interpreting current and future data. The standard approach, namely Eulerian perturbation theory, is unsatisfactory for at least three reasons: there is no clear expansion parameter since the density contrast is not small everywhere; it does not consistently account for deviations at large scales from a perfect pressureless fluid induced by short-scale non-linearities; for generic initial conditions, loop corrections are UV divergent, making predictions cutoff dependent and hence unphysical. I will present the systematic construction of an Effective Field Theory of Large Scale Structures and show that it successfully addresses all three issues. The idea is to smooth the density and velocity fields on a scale larger than the non-linear scale. The resulting smoothed fields are then small everywhere and provide a well-defined small parameter for perturbation theory. Smoothing amounts to integrating out the short scales, whose non-linear dynamics is hard to describe analytically. Their effects on the large scales are then determined by the symmetries of the problems. They introduce additional terms in the fluid equations such as an effective pressure, dissipation and stochastic noise. These terms have exactly the right scale dependence to cancel all divergences at one loop, and this should hold at all loops. I will present a clean example of the renormalization of thetheory in an Einstein deSitter universe with self-similar initial conditions and discuss the relative importance of loop and effective corrections.
Feb 8, Friday 12:00 pm (INPA talk)
Paul Ricker, UIUC
LBL Bldg. 50, room 5026 (the INPA common room)
"AGN Feedback and Mass-Observable Scatter in Galaxy Clusters"
For more than a decade now it has been widely appreciated that active galactic nuclei at the centers of galaxy clusters can heat and disrupt the intracluster gas on scales of tens of kpc. A variety of subresolution models have been proposed to introduce these effects into hydrodynamic simulations of cluster formation. Meanwhile, the importance of clusters as cosmological probes has motivated a number of large cluster surveys in different wavebands. These surveys rely on observed correlations between cluster observable properties and masses in order to derive cosmological constraints. What effect does AGN feedback have on these correlations? Can we exploit observed trends to correct for systematic effects and scatter in them? How important is modeling uncertainty in answering these questions? I will address these topics using results from adaptive mesh refinement simulations.
Feb 11, Monday 12:10 pm (TAC)
Chiaki Hikage, Nagoya
Hearst Field Annex, B5
"Using lensing and correlation measurements to correct Finger-of-God"
For decades, cosmologists have been using galaxies to trace the large-scale distribution of matter. One of the largest systematic uncertainties in this analysis comes from the non-linear redshift distortion, i.e., Finger-of-God effect. If all galaxies sat in the centers of halos, there would be minimal Finger-of-God (FoG) effects and a simple relationship between the galaxy and matter distributions. However, many galaxies, even some of the luminous red galaxies (LRGs), do not lie in the centers of halos. Because the LRG-galaxy lensing and the cross-correlation of LRGs with photometric red galaxies are also sensitive to the off-centered LRGs, we develop an approach for using lensing and correlation measurements to determine the expected amplitude of FoG effects. Using SDSS DR7 LRG and photometric galaxy datasets, we find that 40 per cent of Brightest LRGs are off-centered galaxies in the multiple-LRG systems with typical off-centering radius of #400 kpc/h, and the velocity dispersion of about 500 km/s inside their host halos. The resulting FoG contamination in the LRG power spectrum can be significant at k> 0.1 h/Mpc, which may bias cosmological parameters determined by the shape of the power spectrum, such as the neutrino mass.
Feb 12, Tuesday 1:10 pm (Cosmology-BCCP)
Ryan Hickox, Dartmouth
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"The Dark and the Light: Black Holes, Dark Halos, and their Influence on Galaxy Evolution"
Supermassive black holes are amazingly exotic and yet ubiquitous objects, residing in the centers of essentially all stellar bulges in galaxies. Recent years have seen remarkable advances in our understanding of how these black holes form and grow over cosmic time, and how energy released by active galactic nuclei (AGN) connects the growth of black holes to their host galaxies and large-scale structures. I will review some recent work that explores these connections, with a focus on statistical studies of AGN clustering and the links between black hole growth and and star formation. I will highlight some new insights into how and when AGN "feedback" is important for galaxy evolution, and discuss some prospects for exciting future progress.
Feb 14, Thursday 4:00 pm (RPM)
Kfir Blum, IAS
"CMB Non-Gaussianity from Recombination and Hints for Dark Matter off the Beaten Track"
We show that dark matter annihilation around the time of recombination can lead to growing ionization modes that track the collapse of dark matter overdensities. This amplifies small scale cosmological perturbations to the free electron density by a significant amount. Electron perturbations lead to CMB non-gaussianity, offering a means of detection by Planck and other experiments. We present a novel analytic calculation of CMB non-gaussianity from recombination, improving over previous analyses by taking proper care of small scale electron perturbations and providing a clear identification of the relevant physical processes. We show that, even though electron perturbations can be markedly boosted compared with the standard model prediction, the effect of dark matter annihilation in the CMB bispectrum will be difficult to detect.
Feb 14, Thursday 4:10 pm (Astronomy Colloquium)
Alison Coil, UCSD
1 Le Conte
"What Shuts Down Star Formation in Galaxies?"
The main question I will address in my talk is what shuts down star formation in galaxies. I will highlight recent observational work on outflowing galactic-scale winds in post-starburst and AGN host galaxies and the potential impact of these winds on star formation in these galaxies. I will present new work on which galaxies host accreting supermassive black holes and the lack of evidence for these black holes impacting their host galaxies. Finally, I will show what galaxies look like when their star formation is being shut down and what we can learn from the morphological transformations they undergo during this process. At the end I will briefly mention a new Keck survey that several UC faculty members, including myself and your own Mariska Kriek, are leading to study even more distant galaxies with large, statistical samples.
Feb 15, Friday 12:00 pm (INPA talk)
Edward Macaulay , Oxford
LBL Bldg. 50, room 5026 (the INPA common room)
"Cosmology with Galaxy Redshifts and Peculiar Velocities - Current Mysteries and Future Prospects"
Galaxy redshift and peculiar velocity surveys provide a wealth of insight on cosmology, dark matter, and dark energy. Peculiar velocities can be measured at z=0 with hundreds of luminosity distances, or inferred at z>0 with Redshift Space Distortions (RSDs) from thousands of redshifts. In this talk, I'll present results with both methods which can appear in tension with Lambda-CDM. Many recent RSD measurements are systematically lower than LCDM, hinting that w>-1 (although with a surprisingly low scatter in the data). At z=0, the velocity dipole is several times higher than LCDM. I'll show results from the COMPOSITE peculiar velocity catalogue - the largest to date - and show that the tension with LCDM is dramatically reduced with higher-order moments of the velocity field, and present new, unbiased measurements of the matter power spectrum. I'll then present forecast results for future velocity and redshift surveys, in particular WEAVE - a new, extremely large redshift survey on the William Herschel Telescope - and compare the results to a survey similar to the Euclid spectroscopic survey. I'll show that both surveys will measure powerful and complementary results for dark energy, and forecast measurements for the properties of neutrinos, axions, and modified gravity.
Feb 19, Tuesday 1:10 pm (Cosmology-BCCP)
Stanley Seibert, U Penn
Hearst Field Annex, B1 (not videoconferenced to 50-5026)
"Taking Inventory of the Universe: Exploring the Mystery of Dark Matter with the MiniCLEAN Experiment"
Astronomical observations have produced a tremendous amount of evidence that the gravitational interactions we observe in the cosmos cannot be produced entirely by the particles in the Standard Model. The dark matter hypothesis can explain this mystery by postulating an additional kind of matter that does not interact electromagnetically. But can we detect a new particle in the lab that is even more elusive than the neutrino? I will review the current state of experimental results in the search for dark matter, and describe the upcoming MiniCLEAN experiment, the next member of the DEAP/CLEAN family of dark matter experiments. Coming online this summer, MiniCLEAN will use liquid argon scintillation to search for weakly interacting massive particles, a favored dark matter candidate. The technology is highly scalable, with a direct development path to 10-100 ton argon or neon target masses that can be used in both solar neutrino and dark matter studies.
Feb 26, Tuesday 1:10 pm (Cosmology-BCCP)
Peter Sorensen, LLNL
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Prospects for direct detection of dark matter in 2013 and beyond"
I will discuss efforts to directly detect interactions of galactic dark matter particles, with a focus on dual phase liquid xenon detector technology. First results from the 300 kg LUX experiment are expected before the end of 2013, placing LUX at the state of the art sensitivity over much of the mass range expected for Weakly Interacting Massive Particles (WIMPs). I will discuss the Achilles' Heel of this very successful detector technology, the nuclear recoil energy scale, and plans to address it. LUX was designed to detect WIMPs, and while the WIMP hypothesis is very compelling, it is not the only possibility. I will describe efforts to adapt liquid xenon detector technology to search for dark matter particles with non-weak scale masses, via "non-standard" detection techniques. Finally, I will discuss what we can expect from next-generation experiments such as LZ.
Feb 28, Thursday 4:10 pm (Astronomy Colloquium)
Miguel Morales, Washington
1 Le Conte
Peering through the EoR window with the Murchison Widefield Array
Measurement of the spatial distribution of neutral hydrogen via the redshifted 21 cm line promises to transform our knowledge of the Epoch of Reionization (EoR). In my talk I will give an accessible introduction to this new field, discuss how we plan to observe the faint 21 cm fluctuations in the face of strong foregrounds, and show our latest results from prototype and early commissioning observations with the MWA as we start to peer through the EoR window with the first generation of EoR observatories.

January 2013:
Jan 11, Friday 12:00 pm (INPA talk)
Norihiro Tanahashi, Davis
LBL Bldg. 50, room 5026 (the INPA common room)
"Gravitational wave signal from massive gravity"
Massive gravity theories have been attracting a great deal of interest partly because graviton mass may give an alternative explanation for the accelerated expansion of the universe. We argue how to probe features of the massive gravity theories focusing on the observations of stochastic gravitational wave background generated in the inflationary era. We conduct the analysis based on a general quadratic action for those theories. As a result, we find that a universal feature is a sharp peak appearing in the gravitational wave spectrum, from which we may extract information on the graviton mass and also on the inflationary era. We also discuss the detectability of such a gravitational wave signal using the future-planned gravitational wave observatories.
Jan 15, Tuesday 12:00 pm (INPA talk)
Tamara Davis, Queensland
LBL Bldg. 50, room 5026 (the INPA common room)
The WiggleZ Dark Energy Survey - Final Results
Observations are now complete for the WiggleZ dark energy survey and we have mapped the positions of 219,682 bright blue galaxies out to a redshift of about z=1, over a cubic giga-parsec of space. I will present the full complement of cosmological results coming out of this data set. With the addition of WiggleZ data, baryon acoustic oscillations are now able to confirm the acceleration of the expansion of the universe, independent of any supernova data, and this has since been further strengthened by the addition of Baryon Oscillation Spectroscopic Survey (BOSS) data. Arguably the most exciting results are our measurements of the growth of structure out to z~0.8, and measurements of the Alcock-Paczynski effect (sphericity of spheres) that allow us to measure the rate of expansion at different redshifts H(z) without needing a cosmological model. These allow us to distinguish between non-standard models of gravity that are indistinguishable using only measurements of expansion rate. I will also cover our constraints on the mass of the neutrino and the effective number of neutrinos, which are amongst the tightest constraints available from any experiment. Finally, I will show how the large volume we have sampled has allowed us to detect the scale at which the universe transitions from clustered to homogeneous, confirming one of the cornerstones of modern cosmology. The WiggleZ data have now been made public, and include data, random catalogues, and lognormal realisations. With it we have also released our CosmoMC module so our data can easily be included in your own cosmological analyses.
Jan 18, Friday 12:00 pm (INPA talk)
Morag Scrimgeour, Univ of Western Australia
LBL Bldg. 50, room 5026 (the INPA common room)
"Large-scale homogeneity vs. small-scale inhomogeneities: testing #CDM with large-scale structure"
The most fundamental assumption of the standard cosmological model (LambdaCDM) is that the Universe is homogeneous on large scales. This is not true on small scales, and some studies suggest that galaxies follow a fractal distribution up to very large scales (~200 h-1 Mpc or more), whereas #CDM predicts homogeneity at ~100 h-1 Mpc. We have tested this using the WiggleZ Dark Energy Survey, a UV-selected spectroscopic survey of ~200,000 luminous blue galaxies up to z=1, with the Anglo-Australian Telescope. The large volume and depth of WiggleZ allows us to probe the transition of the galaxy distribution to homogeneity on large scales, and see if this is consistent with a #CDM prediction. Conversely, the properties of small-scale inhomogeneities are an important probe of cosmology. The growth of primordial density perturbations to the large-scale structures present in the Universe today depends on the interplay between cosmic expansion and gravitational interaction. We use N-body simulations to investigate ways galaxy peculiar velocities, arising from these density inhomogeneities, can be used as an independent probe of cosmology.
Jan 25, Friday 12:00 pm (INPA talk)
Eric Baxter, Chicago
LBL Bldg. 50, room 5026 (the INPA common room)
Dark Matter Annihilation and Non-Gaussianity: Looking for Signals of New Physics in the Presence of Astrophysical Backgrounds
The Universe provides us with several unique laboratories for the exploration of physics beyond the Standard Model that is difficult or impossible to measure in the laboratory. In this talk, I will focus on two astrophysical probes of beyond Standard Model physics. First, by measuring gamma-ray photons produced by dark matter annihilations occurring in dark matter subhalos, we can constrain the particle properties of dark matter. Second, from redshifted 21 cm observations of the ionization field during reionization, we can place constraints on non-Gaussianity, which in turn tells us about the physics of inflation. The common challenge presented by these two measurements is separating a small signal of new physics from poorly constrained astrophysical backgrounds. Addressing this challenge will be a theme of the talk.
Jan 29, Tuesday 1:10 pm (Cosmology-BCCP)
Ian McGreer, Arizona
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Quasar evolution at high redshift from optical surveys"
Observations of the quasar luminosity function at high redshift tell a key part of the history of massive black hole evolution. High redshift quasars are more closely connected to their seed black holes, and their rapid growth -- reaching a billion solar masses in under a Gyr -- may point to highly efficient accretion mechanisms that are relatively unchecked by feedback effects. I will summarize three recent programs that greatly enhance our understanding of the evolution of the quasar luminosity function at high redshift: 1) the BOSS survey, comprising over 20,000 quasars at 2.2 < z < 3.5 in the DR9 complete sample, 2) a survey of faint z~5 quasars in the SDSS Stripe 82 region drawn mainly from MMT spectroscopy, and 3) an HST/WFC3 Snapshot program constraining the rate of gravitational lensing in z~6 quasars. A simple picture emerges from these observations, namely that the characteristic luminosity brightens by a factor of ~10 from z=2 to z=6, while the total number density declines exponentially; this is in contrast to the pure luminosity evolution seen from z=2 to z=0 and is likely connected to changes in accretion and feedback modes near the peak of quasar activity. Finally, I will assess the contribution of quasars to reionization and revise constraints on the duration of reionization derived from quasar spectra.

December 2012:
Dec 14, Friday 12:00 pm (INPA talk)
Vera Gluscevic, Caltech
LBL Bldg. 50, room 5026 (the INPA common room)
"CMB as a Probe of New Physics: The Story of Cosmic Birefringence"
Cosmological birefringence is a postulated rotation of the linear polarization of photons that arises due to a Chern-Simons coupling of a new scalar field to electromagnetism. In particular, it appears as a generic feature of simple quintessence models for Dark Energy, and therefore, should it be detected, could provide insight into the microphysics of cosmic acceleration. Prior work has sought this rotation, assuming the rotation angle to be uniform across the sky, by looking for the parity-violating TB and EB correlations in the CMB temperature/polarization. However, if the scalar field that gives rise to cosmological birefringence has spatial fluctuations, then the rotation angle may vary across the sky. In this talk, I will present the results of the first CMB-based search for direction-dependent cosmological birefringence, using WMAP-7 data, and report the constraint on the rotation-angle power spectrum for all multipoles up to the resolution of the instrument. I will discuss the implications for a specific models for rotation, and show forecasts for Planck and future experiments. I will then conclude with a brief discussion of other exotic physical models, such as chiral gravity, and astrophysical scenarios, such as inhomogeneous reionization, that can be probed using the same analysis.

November 2012:
Nov 1, Thursday 4:10 pm (Astronomy Colloquium)
Michael Kuhlen, Berkeley
2 Le Conte
"Most Matter is Dark Matter, but that's not all that Matters"
High resolution simulations of Galactic Cold Dark Matter halos reveal huge amounts of substructure, both in configuration space (subhalos) and in velocity space (tidal streams and debris flow). This substructure has important consequences for efforts aiming to detect non-gravitational signatures of dark matter in the sky and in Earth-bound underground laboratories. In this talk I will first review predictions from ultra-high resolution dark matter-only simulations, and then describe two examples of how the inclusion of baryonic physics in simulations alters these expectations. One example is the abundance of massive subhalos, where baryonic physics may help to reconcile the predictions from DM-only simulations with the relatively low number of observed bright Milky Way dwarf satellite galaxies. The other example is the surprising result that baryonic physics may lead to an offset between the point of maximum dark matter density and the dynamical center of the Galaxy, which could significantly alter theoretical expectations for the dark matter annihilation signal from the Galactic Center.
Nov 6, Tuesday 1:10 pm (Cosmology-BCCP)
Daniel Grin, IAS
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"New light on cosmic initial conditions and dark matter."
Deviations from adiabaticity and Gaussianity in the early universe may shed light on the physics seeding primordial fluctuations. I will discuss statistical techniques to extract local-type non-Gaussianity in the presence of the full CMB transfer function. I will discuss CMB methods to probe isocurvature fluctuations between baryons and dark matter (undetectable in linear theory), as well as a new limit to this mode. Extremely light axionic dark matter (m < 10^{-18}) is in theoretical vogue, and I will discuss ongoing work to search for such axions using large scale structure and the CMB. I will close with the results of a new telescope search for decaying relic axions.
Nov 8, Thursday 4:00 pm (RPM)
Oliver Zahn, UCB
LBL 50A-5132
"New Cosmology from the Microwave Background"
I will talk about two ongoing cosmological revolutions fueled by high angular resolution and high sensitivity observations of the cosmic microwave and infrared backgrounds: constraining the properties of the first galaxies in the Universe (the epoch of reionization) via the kinetic Sunyaev-Zel'dovich effect, and constraining astroparticle physics (in particular massive neutrinos) and gravitational physics (dark energy and matter) through gravitational lensing. I will report on the status and prospects of these endeavors, and discuss how they complement studies of the Lyman-alpha forest and highly redshifted 21-cm radiation, as well as particle physics experiments.
Nov 8, Thursday 4:10 pm (Astronomy Colloquium)
Michael Shull, Colorado
Le Conte
"New Results from the Cosmic Origins Spectrograph: Missing Baryons, AGN, and Reionization Epochs of H and He"
I present a survey of recent ultraviolet spectroscopic observations with the Cosmic Origins Spectrograph, installed on the Hubble Space Telescope in May 2009. I will describe the current status of the local baryon census, observations and theoretical modeling of thermal phases of the intergalactic medium (IGM) and circumgalactic medium (CGM), and the extent of heavy element transport away from galaxy halos. Other new results include the COS composite UV spectrum of quasars, measurements of metal reservoirs in galactic halos, and probes of the Helium-II epoch of reionization at redshifts z = 2.5 to 3.3. We have also used COS "parallel observations" with the new Wide-Field Camera-3 to discover galaxies at z = 8, likely responsible for the IGM reionization of hydrogen.
Nov 9, Friday 12:00 pm (INPA talk)
Azadeh Moradinezhad Dizgah, Buffalo
LBL Bldg. 50, room 5026 (the INPA common room)
"The physics of the early universe from CMB and Large Scale Structure"
Observations of both the Cosmic Microwave Background and large-scale structure are compatible with a spectrum of nearly scale-invariant and Gaussian primordial perturbations, in agreement with the predictions of the simplest inflationary models. However, inflation is not the only mechanism to generate cosmological perturbations consistent with data. In the first part of this talk I focus on the questions of what kind of cosmic evolution can give rise to the perturbations that can seed the structure in the universe. The second half of the talk is concerned with searching for a new probe of primordial non- Gaussianity to study the interactions during inflation. In particular I will discuss the possible imprint of primordial non-Gaussianity on dark matter halo profiles and present some preliminary results.
Nov. 9, Friday 3:00 pm (SSL Colloquium)
Michael Sholl, UC Berkeley
Addition Conference Room, SSL (shuttle from mining circle 2:40 pm)
"BigBOSS: A stage IV dark energy redshift survey"
BigBOSS is a Stage IV dark energy experiment based on proven techniques to study baryon acoustic oscillations and the growth of large scale structure. The 2010 Astronomy and Astrophysics Decadal Survey labeled dark energy as a key area of exploration. BigBOSS is designed to perform a 14,000 square degree survey of 20 million galaxies and quasi-stellar objects. The project involves installation of a new instrument on the Mayall 4m telescope, operated by the National Optical Astronomy Observatory. The instrument includes a new optical widefield corrector, a 5,000 fiber actuator system, and a multi-object spectrometer. Systems engineering flowdown from data set requirements to instrument requirements are discussed, along with the trade considerations and a pre-conceptual baseline design of the widefield optical corrector, spectrometer and fiber positioner systems.
Nov 13, Tuesday 1:10 pm (Cosmology-BCCP)
Rennan Barkana, Tel Aviv
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Detecting the First Stars from Redshift 20"
Understanding the formation and evolution of the first stars and galaxies is one of the exciting frontiers in astronomy. Since the universe was filled with neutral hydrogen at early times, the most promising method for observing the epoch of the first stars is using the prominent 21-cm spectral line of hydrogen. Current observational efforts are focused on a cosmic age of 500 million years, with earlier times considered much more challenging. We show that stars from a much earlier era may be observable as a result of a recently noticed effect of different motions of the dark matter and the ordinary matter in the early universe. We produce simulated maps of the first stars and show that these relative motions significantly enhance large-scale fluctuations and produce prominent structure on the scale of a degree in the 21-cm intensity distribution. The particular signature expected for this effect in the 21-cm power spectrum should make it easier to confirm the existence of million solar-mass halos at early times.
Nov 16, Friday 3:00 pm (SSL Colloquium)
Nico Cappelluti, INAF-Bologna, Italy
Addition Conference Room, SSL (shuttle from mining circle 2:40 pm)
"Clustering of the Cosmic X-ray Background"
In this talk I will present the state of the art on the studies of AGN clustering in the X-ray band and their applications in understanding the coeval growth of super-massive black holes (SMBHs) and dark matter halos. A well defined picture has been taken up to z~2 while, at high-z, where important physical phenomena connected with SMBH formation take place, the knowledge is still relegated to the study of anisotropies of the unresolved cosmic X-ray background (CXB).I will present recent applications of clustering analysis to the study of clustering patterns of the unresolved CXB fluctuations and their counterparts at IR wavelengths with a the detection of a possible signature of the first black holes in the Universe, through CIB-CXB cross-fluctuation analysis.
Nov 20, Tuesday 1:10 pm (Cosmology-BCCP)
Adam Christopherson, Nottingham
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Cosmological Perturbations: Isocurvature, Vorticity and Magnetic Fields"
In this talk I will discuss some recent, complementary work that I have undertaken using cosmological perturbation theory, a powerful technique for modelling inhomogeneities in the universe. After a brief review of the basics, I introduce isocurvature, or non-adiabatic pressure perturbations, and calculate their spectrum in the settings of standard, concordance cosmology, and inflationary models involving two scalar fields. I then extend the discussion beyond linear perturbations, and show that vorticity can be sourced at second order with only scalar perturbations, the source term being quadratic in the gradients of first order energy density and non-adiabatic pressure perturbations. I present a first estimate of this vorticity's power spectrum, and highlight some potential observational consequences. One of these is the possible sourcing of sizeable magnetic fields, and I briefly sketch some current work on including magnetic fields in perturbation theory in a consistent way. I close with some ideas for future work.
Nov 26, Monday 12:10 pm (TAC)
Debora Sijacki, Harvard
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
Nov 27, Tuesday 1:10 pm (Cosmology-BCCP)
no talk
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
no talk
Nov 30, Friday 12:00 pm (INPA talk)
Michael Mortonson, UCB
LBL Bldg. 50, room 5026 (the INPA common room)

October 2012:
Oct 2, Tuesday 1:10 pm (Cosmology-BCCP)
Andrew Wetzel, Yale
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Galaxy evolution in groups and clusters in a hierarchical Universe"
Satellite galaxies in groups and clusters play a critical role in the picture of galaxy evolution. As many as a third of all galaxies are satellites, and satellite star formation quenching is the dominant process in building the red-sequence population at low stellar mass. I will present an observational and theoretical investigation into the evolution of star formation in satellite galaxies, using the Sloan Digital Sky Survey to examine satellites across a wide range of host halo masses, from massive clusters to the lowest mass dwarf galaxy groups in the local Universe. I will place these results in a fully cosmological context using a high-resolution simulation to track satellite orbits and infall times, showing that satellite star formation histories follow a delayed-then-rapid quenching scenario. Using satellite orbital histories, I also will test various physical mechanisms thought to play a role in quenching satellites. Finally, I will examine the curious evolution of satellites that orbit beyond their host halo's virial radius.
Oct 4, Thursday 4:10 pm (Astronomy Colloquium)
Adam Riess, JHU
2 Le Conte
"Precision Measurement of the Hubble Constant and PASS"
The Hubble constant remains one of the most important parameters in the cosmological model, setting the size and age scales of the Universe. Present uncertainties in the cosmological model including the nature of dark energy, the properties of neutrinos and the scale of departures from flat geometry can be constrained by measurements of the Hubble constant made to higher precision than was possible with the first generations of Hubble Telescope instruments. Streamlined distances ladders constructed from infrared observations of Cepheids and type Ia supernovae with ruthless attention paid to systematics now provide 3.5% precision and offer the means to do much better. While WFC3 has helped open this new route, its full exploitation can come from a new technique, Parallel Astrometric Spatial Scanning (PASS), to measure parallax distances beyond a kilo parsec. I will review recent and expected progress.
Oct 5, Friday 12:00 pm (INPA talk)
Amanda Yoho, CWRU
LBL Bldg. 50, room 5026 (the INPA common room)
"Boosting the Universe: Observational consequences of our motion"
The Cosmic Microwave Background (CMB), photons from the earliest epoch that are able to free stream towards us, provides a unique opportunity to learn about many properties of the universe we live in. Already, the temperature fluctuations of the CMB have been studied by the Wilkinson Anisotropy Probe (WMAP) and have allowed many cosmological parameters to be pinned down to within a percent error. However, there are many more mysteries to be uncovered by precise measurements of the CMB polarization of these photons and weak lensing fields. Only with a robust understanding of the possible contaminants and astrophysical effects that can deform the measured fields will we be able to accurately characterize which models are favored over others. I will present here the challenges that will arise when analyzing data from future cosmological surveys due to our motion through the universe, and describe methods for accurately accounting for this particular systematic effect.
Oct 9, Tuesday 1:10 pm (Cosmology-BCCP)
Mark Wyman, Chicago
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Gravity's Dark Side"
Why is the Universe's expansion rate accelerating today? This question lies at the heart of modern cosmology. In my talk, I will argue that today's acceleration compels us to consider that General Relativity may need to be extended. If gravity has a new dark sector, it should be detectable by the powerful tools of modern observational cosmology. Today, I will focus on a theory that extends GR by giving the graviton a mass. This theory may explain today's accelerated expansion, and has distinctive observational consequences. I will discuss three aspects of this theory. First, I will describe its puzzling self-accelerating solutions. Second, I will present results from N-body simulations that show an intriguing pattern of enhanced large scale structure growth. Finally, I will describe a novel way that this theory alters weak gravitational lensing.
Oct 12, Friday 12:00 pm (INPA talk)
Louis Strigari, Stanford
LBL Bldg. 50, room 5026 (the INPA common room)
"Multiple facets of Galactic dark matter searches"
I will discuss two distinct aspects of searches for unknown constituents of the Milky Way Galaxy. I begin by covering recent advances in searches for particle dark matter, including reviewing results from indirect and direct searches. I will interpret the modern experimental results in the context of theoretical particle dark matter models. For the second part of the talk, I will discuss the implications of new microlensing results that indicate that 'free floating planets' are common in the Galaxy. I will discuss the theoretical origin of these objects, and the potential for future wide field surveys to significantly improve the census of these objects.
Oct 16, Tuesday 1:10 pm (Cosmology-BCCP)
Rachel Bezanson, Yale
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Galaxy quenching and the remarkable stability of the velocity dispersion function since z~1.5"
Massive galaxies have evolved dramatically in the last 10 billion years, undergoing dramatic changes to their sizes, shapes and stellar populations. In the context of this evolution, I will argue that velocity dispersion is the most fundamental property of galaxies, especially when attempting to identify unique populations of galaxies across cosmic time. Although directly measuring velocity dispersion is observationally expensive, we introduce inferred velocity dispersion as implied by the stellar mass, Sersic index and effective radius of galaxies in the SDSS. We calculate inferred velocity dispersions for galaxies in the UDS and NMBS Cosmos Surveys and derive the velocity dispersion function (VDF) out to z=1.5, both for the entire population and separately for star-forming and quiescent galaxies. Remarkably, we find that overall the VDF is quite stable, providing tentative evidence for inside-out galaxy growth. Specifically, we find that galaxies with high velocity dispersions form early: the number density of both star-forming and quiescent galaxies remains roughly constant with time. Additionally we find that the number of star-forming galaxies as a function of velocity dispersion is quite stable with time. The only galaxy population showing strong evolution are quiescent galaxies with low inferred dispersions, for which number density increases by a factor of ~4 since z=1.5. We show that our results are qualitatively consistent with a simple model in which star-forming galaxies quench and are added to the quiescent population. In order to compensate for this migration, the velocity dispersions of star-forming galaxies must increase, with a rate that increases with dispersion. This model predicts that there must be a significant population of quenching and recently quenched galaxies at z>1. Finally, I will present evidence for this model with the discovery of galaxies at z~1.5 with high velocity dispersions and strong Balmer lines.
Oct 18, Thursday 4:00 pm (RPM)
Ludo Van Waerbeke, UBC
LBL 50A-5132
"Weak Lensing with CFHTLS"
The CFHTLenS team has been working full time in the past 3 and half years on the analysis of the 150 sq.deg. of the Canada France Telescope Legacy Survey (CFHTLS). Our main goal was gravitational lensing science, and most of the practical work focussed on measuring the galaxy shapes and photometric redshifts with the best possible precision. In my talk I will present some of the science results, most of them are either accepted or under review. I will highlight some of the lessons learned from this project that will be useful for future lensing surveys. Our upcoming data release (november 1st 2012) will give full access to all our data products through the Canadian Astronomy Data Center (CADC).
Oct 19, Friday 2:00 pm Note special time (INPA/Cosmology)
Ying Zu, OSU
LBL 50-5026 (INPA Room)
"Cluster Cross-Correlation Cosmology"
Clusters are powerful probes of cosmic growth, which is the key to solving the mystery of cosmic acceleration. I will discuss two methods that investigate the distribution and motion of correlated matter and galaxies around clusters, one through cluster--shear correlation, the other through cluster--galaxy correlation in redshift space. I will present simple phenomenological models to explain the correlation signals observed in the Sloan Digital Sky Survey. Finally, I will discuss the prospect of combining the two methods, each of which probes a different part of the cluster potential, for revealing deviations from General Relativity on cosmological scales.
Oct 19, Friday 3:00 pm (SSL Colloquium)
Joaquin Vieira, Caltech
Addition Conference Room, SSL (shuttle from mining circle 2:40 pm)
"High-redshift, gravitationally lensed, dusty, starburst galaxies revealed by the South Pole Telescope and ALMA"
The South Pole Telescope has systematically identified large numbers of high-redshift strongly gravitationally lensed systems. These sources are selected by their extreme mm flux, which is largely independent of redshift and lensing configuration. I will report results from the first blind redshift survey undertaken with the recently commissioned Atacama Large Millimeter Array (ALMA). We targeted 26 rare, extraordinarily bright, dusty sources selected from a 2500 deg^2 mm survey conducted by the SPT and obtained redshifts via molecular carbon monoxide (CO) lines. We determine that roughly 40% of these sources lie at z>4, indicating the fraction of dusty starburst galaxies at high-redshift is far higher than previously thought. Two sources are at z=5.7, placing them among the highest redshift starbursts known, and demonstrating that large reservoirs of molecular gas and dust can be present in massive galaxies near the end of the epoch of cosmic reionization. These sources were additionally targeted with high resolution imaging with ALMA, unambiguously demonstrating them to be strongly gravitationally lensed by foreground structure. We are undertaking a comprehensive and systematic followup campaign to use these ``cosmic magnifying glasses'' to study the infrared background in unprecedented detail, inform the condition of the interstellar medium in starburst galaxies at high redshift, and place limits on dark matter substructure. I will discuss the scientific context and potential for these strongly lensed starburst galaxies, give an overview of our team's extensive followup efforts, and describe our latest science results.)
Oct 23, Tuesday 1:10 pm (Cosmology-BCCP)
Peter Behroozi, Stanford
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Galaxy Star Formation Efficiency from z=0 to z=8"
We present a robust, self-consistent, semi-empirical model which matches observed galaxy stellar masses and star formation rates over nearly all of cosmic history. Key results include constraints on star formation rates as a function of halo mass, average star formation histories for galaxies from z=0 to z=8, and the buildup of the intracluster light as a function of halo mass and time. We also examine the connections between halo growth and galaxy growth, and we find that the universe's star formation history since z~4 can be explained by a star formation efficiency which is strongly dependent on mass but only weakly dependent on time. We discuss the implications of this latter finding, especially in terms of the impact on black hole/supernova feedback models and the impact on the shape of the cosmic star formation rate for 0 < z < 8.
Oct 25, Thursday 4:10 pm (Astronomy Colloquium)
Marusa Bradac, Davis
2 LeConte Hall
"Dark Matter and First Galaxies Light Up"
The cluster of galaxies 1E0657-56 has been the subject of intense research in the last few years. This system is remarkably well-suited to addressing outstanding issues in both cosmology and fundamental physics. It is one of the hottest and most luminous X-ray clusters known, and is unique in being a major supersonic cluster merger occurring nearly in the plane of the sky, earning it the nickname "the Bullet Cluster". The newest HST/WFC3 data has revealed further interesting properties of this cluster. We have also studied a couple of new Bullet-like cluster, MACSJ0025-1222, A520, and DLSCL J0916.2+2951. Allthough they do not contain a low-entropy, high density hydrodynamical `bullet,' these clusters exhibits many similar properties to the Bullet Cluster. Furthermore, the advent of Wide Field Camera 3 (WFC3) on HST enabled us to detect galaxies at z~7. They are likely beacons of the epoch of reionization, which marked the end of the so-called ``Dark Ages'' and signified the transformation of the universe from opaque to transparent. Clusters of galaxies, when used as cosmic telescopes, can greatly simplify the task of studying and finding these galaxies. With a massive cluster one can gain several magnitudes of magnification over a typical observing field, enabling imaging and spectroscopic studies of intrinsically lower-luminosity galaxies than would otherwise be observable, even with the largest telescopes. In this talk I will present the new spectroscopy results we have obtained with LRIS@Keck and FORS2@VLT to study these galaxies behind some of the most powerful cosmic telescopes and discuss our future goals with MOSFIRE@Keck and Spitzer.
Oct 25, Thursday 4:00 pm (RPM)
Anze Slosar, Brookhaven
LBL 50A-5132
"BOSS Lyman-alpha Forest BAO Detection"
I will present a measurement of baryon acoustic oscillation features at z ~ 2.4 in the three-dimensional correlation function of the transmitted flux fraction in the Lyman-alpha forest of BOSS quasars. Our results are derived from a sample of ~50K high-redshift quasars from the Data Release 9 of the Baryon Oscillation Spectroscopic Survey (BOSS), part of the Sloan Digital Sky Survey (SDSS-III). A peak in the correlation function is seen at a position consistent with that expected from baryon acoustic oscillations and Lambda-CDM cosmology. I will discuss statistical significance and potential sources of systematic error.
Oct 26, Friday 12:00 pm (INPA)
Nishikanta Khandai, BNL
LBL 50-5026 (INPA Room)
"The large scale clustering of the Lyman alpha forest"
We use a large cosmological hydrodynamical simulation to study the large scale clustering of the lyman alpha forest. We extract the large scale bias and the redshift space distortion parameter \beta from the power spectrum of the lyman alpha forest. We find that both bias and beta evolve strongly with redshift with (bias,beta) = (-0.12,1.4) at z=2 and (bias,beta) = (-0.42,0.94) at z=3.5. We use two different methods to extract bias and beta. We also look at the variation of these parameters as a function of mean flux and conclude with a discussion on these methods.
Oct 26, Friday 3:00 pm (SSL Colloquium)
Mariska Kriek, UCB
Space Sciences Lab: Annex Conference room
"The Formation Histories of Massive Galaxies"
In the past decade, photometric and spectroscopic galaxy surveys have started to explore the Universe at redshifts z=1-3, the epoch during which galaxies and black holes appear to grow most rapidly. It was found that the galaxy population at this early epoch is quite diverse, and ranges from starburst galaxies with large and irregular morphologies to very small galaxies with quiescent stellar populations. However, despite this tremendous progress, these studies are hampered by the small sizes of spectroscopic galaxy samples, whereas much larger photometric samples lack the required spectroscopic information. I will discuss two observing programs which compromise between these two techniques: the 3D-HST survey, a grism survey with HST/WFC3 and the NEWFIRM Medium-Band Survey. I will show how these studies have contributed to our understanding of the formation histories of massive galaxies. Furthermore, I will present new stellar kinematic measurements of distant galaxies obtained using deep near-infrared spectroscopy, and discuss the implications for the structural evolution of galaxies.
Oct 30, Tuesday 1:10 pm (Cosmology-BCCP)
Kiyo Masui, CITA
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Pioneering 21 cm intensity mapping at the Green Bank Telescope"
The 21 cm radio line, from the hyperfine energy splitting in neutral hydrogen, has long been a useful tool in radio astronomy for studying the local universe. More recently it has been proposed that the line might be used to study a wide range of problems at high redshift, including reionization at z~8, large scale structure, galaxy formation and dark energy at z~1, and even the initial conditions of the universe at z>10. I will describe the first attempts to use the line to study large scale structure using a method referred to as intensity mapping. Our collaboration uses the Green Bank Telescope to observe the 21 cm line at low resolution in the redshift range 0.6 < z < 1. With promising early results from cross correlating with the WiggleZ galaxy survey, we are now pushing toward a completely autonomous detection.

September 2012:
Sep 4, Tuesday 1:10 pm (Cosmology-BCCP)
no talk
Sep 10, Monday 4:15 pm (Physics Colloquium)
Sean Carroll, CalTech
1 Le Conte
"The Origin Of The Universe And The Arrow Of Time"
Over a century ago, Boltzmann and others provided a microscopic understanding for the tendency of entropy to increase. But this understanding relies ultimately on an empirical fact about cosmology: the early universe had a very low entropy. Why was it like that? Cosmologists aspire to provide a dynamical explanation for the observed state of the universe, but have had very little to say about the dramatic asymmetry between early times and late times. I will discuss whether the problem of low-entropy initial conditions can be alleviated within the context of a multiverse.
Sep 11, Tuesday 1:10 pm (Cosmology-BCCP)
Drew Newman, Caltech
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"The Density Profiles of Galaxy Clusters Over 3 Decades in Radius"
The density profile of halos composed purely of cold dark matter (CDM) is precisely predicted in numerical simulations. Observations of real systems ranging from dwarf galaxies to galaxy clusters have suggested deviations from this form on small scales. This could reflect the role of baryons in the formation of these systems, or alternatively may inform us about the dark matter particle. I will present observations of 7 massive, relaxed clusters at z~0.2-0.3 using the techniques of strong and weak gravitational lensing, coupled with spatially-resolved stellar kinematics within the centrally-located brightest cluster galaxies (BCGs). Combining these high-quality data yields precise constraints on the density profile from ~3 kpc to 3 Mpc. At radii >~ 5-10 kpc, we find that the total density profiles (dark and baryonic) agree surprisingly well with state-of-the-art cluster simulations containing only CDM, despite the significant contribution of stars in the BCG on these scales. I will show how stellar kinematic data at small radii can be used to separate stellar and dark mass and isolate the inner dark matter density profiles. These are found to be shallow compared to CDM cusps and correlate with the properties of the BCG, demonstrating a close connection between the inner halo and the assembly of the central galaxy. I will discuss physical mechanisms proposed to account for this.`
Sep 18, Tuesday 1:10 pm (Cosmology-BCCP)
Ken Wong, Arizona
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Optimal Mass Configurations for Lensing High-Redshift Galaxies (and how to find them in the SDSS!)"
We investigate whether lines of sight containing multiple cluster-scale halos are the best cosmic telescopes for lensing high-redshift (z~10) sources into detectability. For lines of sight of fixed angular size and total mass, we test how the lensing cross section and the number of faint galaxies detected at high redshift change as that mass is distributed among multiple halos, as well as which physical properties of the halos are most important. We find that multiple projected halos are can result in improvement in the detection of faint, high-z sources compared to single halos of equivalent total mass due to the interactions among the lensing potentials when the projected halos overlap. Using integrated LRG luminosity density as a tracer of mass, we have identified lines of sight in the SDSS that are likely to contain the largest total integrated masses. These fields contain a diversity of single massive clusters and chance alignments of multiple halos in projection, and are likely to be among the best gravitational lenses known.
Sep 20, Thursday 4:00 pm (RPM)
Michael Mortonson, UCB/LBNL
LBL 50A-5132
"Observational Probes of Cosmic Acceleration"
Over the past decade, a variety of observations have solidified the evidence for an accelerating Universe. In the next decade, larger surveys will attempt to pinpoint the physical explanation for cosmic acceleration by increasing the precision of established methods and enabling new techniques to test models of dark energy and modified gravity. I will review the main observational tools available for investigating cosmic acceleration, using both recent results from surveys such as BOSS and forecasts for proposed surveys to demonstrate the complementarity between probes including Type Ia supernovae, baryon acoustic oscillations, and weak lensing. I will show how these forecasts can be used to study the sensitivity of predicted constraints on dark energy and modified gravity parameters to survey properties and theoretical assumptions, providing guidance for optimizing observational strategies. An unambiguous and robust explanation for the accelerating Universe can only be obtained by a program that combines and advances several probes of the expansion history and the growth of large-scale structure.
Sep 21, Friday 12:00 pm (INPA talk)
Lavinia Heisenberg, Univ of Zurich
LBL Bldg. 50, room 5026 (the INPA common room)
"From Einstein through Vainshtein to dRGT design"
Recently there has been a successful non-linear covariant ghost-free generalization of Fierz-Pauli massive gravity theory, the dRGT theory. I will explore the cosmology in the decoupling limit of this theory. Furthermore, I will discuss a Proxy to dRGT and study the cosmology there as well and compare the results.
Sep 25, Tuesday 1:10 pm (Cosmology-BCCP)
Blake Sherwin, Princeton
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"CMB Lensing Measurements: Mapping Dark Matter with ACT and ACTPol"
Measurements of lensing in the cosmic microwave background (CMB) directly probe the projected distribution of dark matter out to high redshifts. I will describe the first detection of the power spectrum of CMB lensing with the Atacama Cosmology Telescope (ACT) and its cosmological implications, and will show results from cross-correlations of ACT CMB lensing maps with quasars, galaxies and other tracers of dark matter. I will then explain the great scientific potential of upcoming polarization lensing measurements with ACTPol, and will discuss the development of a lensing pipeline for this experiment.
Sep 27, Thursday 4:10 pm (Astronomy Colloquium)
Naveen Reddy, Riverside
2 Le Conte
"The Characteristic Star Formation Histories of Galaxies from z~2-7"
We use a large spectroscopic sample of L* galaxies at redshifts 1.5 < z < 3.4 with Keck, Hubble, and Spitzer observations, to study the average star formation history of galaxies at z~2. We first perform a detailed comparison between the bolometric SFRs of z~2 galaxies and those obtained from SED-fitting. This comparison suggests that exponentially-declining models are, in general, a poor representation of the star formation histories at z~2. Taking into account a number of systematic biases, we find a near unity relationship between SFR and stellar mass for z~2 galaxies. The median specific SFR of our sample, when placed in context with the median specific SFRs found for higher redshift dropout samples, suggests a scenario where SFRs rise roughly exponentially with time. We find that the net cold gas accretion rate, as inferred from the specific SFR and the K-S relation, is typically 2-3 times larger than the SFR at z>4. However, if we evolve to higher redshift the star formation histories and the masses of the halos that are expected to host L* galaxies at z~2, then we find that 4 actually contribute to star formation at those epochs. These results highlight the relative inefficiency of star formation even at early cosmic times when galaxies were first assembling.
Sep 28, Friday 12:00 pm (INPA talk and Cosmology-BCCP talk)
Antonio Cuesta, Yale
LBL Bldg. 50, room 5026 (the INPA common room)
"Measuring BAO in the reconstructed field of SDSS galaxies"
The measurement of the Baryon Acoustic Oscillation (BAO) feature imprinted in the clustering distribution of galaxies is becoming a mainstream method for large galaxy surveys to determine the relation between distance and redshift. However, obtaining precise determinations of the distance-redshift relation requires a low uncertainty in the position of the BAO, which is usually achieved by extending the survey to probe a larger volume. In this talk I will describe how a simple method dubbed "reconstruction" is able to reduce the uncertainties in these measurements by partially undoing the effects of non-linear evolution responsible of washing away the BAO. The reduction in the error bar is therefore given for free, without the need for further additional observations, since the method uses information from the density field that is not captured by two-point clustering statistics. I will describe how reconstruction has successfully been applied for the first time this year to the LRG and CMASS galaxy samples from Sloan Digital Sky Survey, and how cosmological constraints benefit from these high-precision BAO measurements.

August 2012:
Aug 14, Tuesday 1:10 pm (Cosmology-BCCP)
Colin Hill, Princeton
Hearst Field Annex, B5
"Cosmological Constraints from Moments of the Thermal Sunyaev-Zel'dovich Effect"
The thermal Sunyaev-Zel'dovich (tSZ) effect is a distortion of the spectrum of the cosmic microwave background (CMB) due to the inverse Compton scattering of CMB photons off hot electrons in the intracluster medium (ICM) of galaxy clusters. The tSZ effect is a powerful cosmological probe, but the traditional statistic with which it has been characterized -- the power spectrum -- suffers from systematic uncertainty due to poorly-understood physics in the ICM. In this talk I will describe a different approach to studying the tSZ effect through moments of the temperature fluctuation PDF. In particular, I will highlight applications of the tSZ skewness, which is more sensitive to cosmology than the variance (or, equivalently, power spectrum), and is dominated by contributions from clusters that have been well-observed with X-rays and other techniques. I will describe our recent detection of the tSZ skewness with the Atacama Cosmology Telescope, and will present new methods to combine the skewness and variance to circumvent long-standing uncertainties in tSZ measurements due to ICM astrophysics, thus allowing improved constraints on a number of cosmological parameters.
Aug 20, Monday 12:10 pm (TAC Seminar)
Romain Teyssier, Zurich/Saclay
Hearst Field Annex, B5
New Frontiers in Computational Galaxy Formation
I will present recent results obtained with the Adaptive Mesh Refinement technique of galaxy formation, using both idealized numerical experiments and fully cosmological simulations. I will demonstrate that feedback processes are fundamental ingredients in defining the bulk properties of galaxies, both on small and on large scales. I will finally present a newly developed radiative transfer module developed for the RAMSES code, allowing us to perform full radiation hydrodynamics simulations of galaxy formation.
Aug 28, Tuesday 1:10 pm (Cosmology-BCCP)
Matt Becker, Chicago
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Weak Lensing Simulations and Precision Cosmology with Large Area Sky Surveys"
Weak lensing measurements are an essential part of near- and long-term large-area sky surveys aimed at an array of scientific goals, like understanding Dark Energy, elucidating further the connection between galaxies and dark matter halos, constraining modifications to General Relativity, etc. The weak lensing community has undertaken extensive simulation efforts, both CCD image simulations and computations of the cosmological weak lensing signals from large-scale structure simulations, in order to address the variety of systematic errors which can adversely effect these measurements and their interpretation. The next logical step in this effort is the construction of mock galaxy catalogs with weak lensing shear signals self-consistently from large-scale structure simulations. While these weak lensing mock galaxy catalogs have easily been made for small patches of sky (~10 square degrees), upcoming large-area sky surveys will image thousands of square degrees or more. I will describe a new multiple-plane ray tracing code which is able to produce full-sky weak lensing deflection, convergence, and shear fields suitable for the construction of weak lensing mock galaxy catalogs for large-area sky surveys. I will also highlight the application of this code to the Dark Energy Survey simulation effort. Finally, I will present a prototypical example of these simulation efforts, my recent work on interpreting weak lensing galaxy cluster mass measurements, emphasizing understanding their scatter and more importantly their potential biases. This work, and ongoing work by others in the Dark Energy Survey collaboration based on these new weak lensing mock galaxy catalogs, illustrates the utility these simulations in understanding systematic errors in current and future weak lensing measurements from large-area sky surveys.
Aug 30, Thursday 4:10 pm (Astronomy Colloquium)
Paul Schechter, MIT
2 Le Conte
"WFIRST: A cold, gold, unobstructed three-mirror-anastigmat with a large HgCdTe focal plane"
Aug 31, Friday 12:10 pm (Astronomy Journal Club)
Paul Schechter, MIT
B5 Hearst Field Annex
"Some things about telescope optics that nobody wanted to know and why they matter for dark energy"
How many wavefront sensors does a telescope need? To what order must the wavefront be measured? How often? The answers to these questions implicit in the design of the LSST -- four wavefront sensors measuring 36 Zernike terms once every 15 seconds -- may seem extreme. But something close to this may be needed to meet the stringent requirements for cosmological weak gravitational lensing measurements. We consider idealized telescopes with infinitely stiff mirrors and report on the GENERIC misalignment aberration patterns that such telescopes produce. By way of example we consider the case of a three mirror anastigmat. We introduce the ``subspace of benign misalignment'' in which the generic misalignment aberration patterns associated with defocus, coma and astigmatism are controlled and zeroed. A minimum of 3 wavefront sensors and control of at least 2 rigid surfaces is needed to stay within the subspace of benign misalignment. One or more additional higher order wavefront sensors may be needed to measure wavefront errors due to non-rigid mirrors.

Cosmology Seminars in Previous Years

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