Upcoming and Previous Seminars

Mar. 4, Tuesday, 11:00 am
Janna Levin, Barnard/Columbia
325 LeConte
"A Periodic Table for Black Hole Orbits"
We are on the verge of a truly remarkable observational possibility: the direct detection of black holes through gravitational radiation. Knowledge of the dynamics around rotating black holes is imperative to the success of gravitational wave observatories. While they have been studied extensively, a general understanding of the elaborate orbits has been elusive. We demonstrate that the entire dynamics around black holes can be understood through a beautiful, geometric taxonomy of perfectly periodic orbits. A remarkable implication of this taxonomy is that the simple precessing ellipse familiar from planetary orbits is not allowed in the strong-field regime. Instead, eccentric orbits trace out precessions of multi-leaf clovers in the final stages of inspiral. Finally, we sketch the potential application of the taxonomy to problems of astrophysical interest.

Mar. 4, Tuesday 1:10 pm
T.J. Cox, Harvard
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Unraveling the Formation History of Elliptical Galaxies"
The idea that galaxies in general, and elliptical galaxies in particular, are shaped by their merger history has gained widespread acceptance. However, a detailed mapping between specific merger histories, and the wide variety of galaxies observed is still uncertain. By using a comprehensive set of numerical simulations, we show that a single disk-disk merger, as originally proposed by the "merger hypothesis," is a plausible mechanism to form many elliptical galaxies provided that dissipation is involved. We also show that additional (merger?) processes are likely needed to form the largest ellipticals and we outline several properties commonly observed in elliptical galaxies that may provide insight into their formation history.

Mar. 6, Thursday 4:10 pm (Astronomy Colloquium)
Hans-Walter Rix, MPIA
1 LeConte Hall
"Do the Milky Way's Outskirts Live up to Cosmological Expectations?"
The current galaxy formation paradigm implies that galaxies, such as our own Milky Way, are 'baryon condensates' at the center of extensive dark matter halos, and exhibit a wealth of detailed substructure that reflects their hierarchical formation: numerous sub-halos and tidally disrupted streams. Only in the local group can we currently put galaxy formation to a test based on its fine-scale predictions. The Sloan Digital Survey, and its follow-on project SEGUE, have just provided an unprecedented data set to study the Milky Way's outskirts, and I will present recent quantitative comparisons between model predictions and these new observations.

Mar. 11, Tuesday 1:10 pm
Andrew Benson, Caltech
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Dark Matter Halo Mergers and Smoluchowski's Equation"
High-accuracy measures of the dark matter halo merger rate are crucial to studying a wide range of astrophysical processes (essentially anything that depends on the growth rate of large scale structure). I will describe constraints on dark matter halo merger rates obtained by utilizing Smoluchowski's coagulation equation, which must be obeyed by any binary merging process which conserves mass. The constraints are consistent with those obtained from fitting to N-body measures of progenitor mass functions, and provide a better match to the evolution of the overall dark matter halo mass function, particularly for the most massive halos. These merger rate solutions are highly accurate, permitting the dark matter halo mass function to be evolved over large redshift intervals with precision of order a few percent.

Mar. 14, Friday 12 noon (INPA Journal Club)
Douglas Spolyar, Santa Cruz
LBL Bldg. 50, room 5026 (the INPA common room)
"The effect of dark matter on the first stars: a new phase of stellar evolution"
Nobel Laureate David Gross recently commented that LHC is being built for Super Symmetry, Super Symmetry, Super Symmetry! The Lightest Super Symmetric Partner (LSP) is arguably the most favored dark matter candidate. In this talk, two mechanism are identified whereby dark matter (DM) in proto stellar halos can dramatically alter the formation of the first stars, which may lead to a new phase of stellar evolution driven by DM annihilation and the LSP in particular.

Mar. 18, Tuesday
Cosmology Astronomy Colloquium Thursday

Mar. 20, Thursday 4:10 pm (Astronomy Colloquium)
David Hogg, NYU
1 LeConte Hall
"The Fastest, Largest, and Least Well-organized Observatory in the World"
Historical plate archives, educational and outreach observatories, and the hard drives of amateurs contain countless images, many of which are uncalibrated as far as scientific uses are concerned. Nonetheless, they contain enormous information about asteroids, stellar proper motions, variability, and transients; indeed many amateurs and educators make important discoveries and measurements each year.
We have built a reliable and robust system that takes as input an astronomical image, and returns as output the pointing, scale, and orientation of that image (the astrometric calibration or WCS information). The system requires no first guess, and works with the information in the image pixels alone. The success rate is very high (~99.9 percent for shallow UV and optical imaging survey data), with essentially no false positives. With lower precision, it also determines the date at which the image was taken, the filter or bandpass, and the photometric zeropoint.
We are using this system to generate consistent and standards-compliant calibration data for all digital and digitized astronomical imaging, no matter what its origin or archival state. This is the first step in a program of making all of the world's heterogeneous astronomical data searchable and interoperable, and organizing the world's amateurs and educators into the largest, fastest, and most reliable observatory in the world.

Mar. 25, Tuesday 1:10 pm
Marcello Cacciato, MPIA
544 Campbell Hall (also videoconferenced to LBL 50F-1647) --Please note different room
"Modeling g-g lensing with the conditional luminosity function"
Galaxy-galaxy (g-g) lensing represents an ideal technique to constrain the dark matter distribution on galaxy scales. The required accuracy in the signal can be achieved only by stacking many foreground galaxies and averaging the ellipticity of the resulting background galaxies. Unfortunately, the stacking procedure complicates any astro-physical interpretation. In order to extract information from the composite g-g lensing signal, a reliable model of the way galaxies populate dark matter haloes is required. Previous attempt were based on simplistic assumptions. We use a more realistic description of the halo occupation statistics based on the conditional luminosity function. It provides a statistical prescription for the number of galaxies with a given luminosity living in dark matter haloes of a given mass. Being 'a priori' constrained by the luminosity dependence of the galaxy clustering, it can be used for predicting the g-g lensing signal without any additional tuning. Our model allows a thorough understanding of the different terms contributing to the signal. We carefully explore the effect of the assumptions entering the model. Our theoretical predictions are in very good agreement with SDSS data. Furthermore, we investigate the feasibility of g-g lensng as a probe for cosmology.

Mar. 28, Friday 12 noon (INPA Journal Club)
Oliver Zahn, Berkeley
LBL Bldg. 50, room 5026 (the INPA common room)
"The state of the art of 21 cm science"
As the only known probe of the evolutionary phase between decoupling of the CMB and z~6, the hydrogen spin-flip transition promises to play a crucial role for our understanding of the universe's dark ages and of reionization. The majority of our Hubble volume should emit in 21 cm, and observations of it promise to constrain more modes for obtaining fundamental cosmological information than any other probe. In practice there are many challenges, such as the orders-of-magnitude brighter galactic foregrounds and the computational requirements associated with doing radio-interferometry at multi-meter wavelengths. I will start with a brief introduction into 21 cm science, highlighting the different stages of spin temperature fluctuations. I will review the theoretical progress made over the last few years in predicting what the signal will look like, and talk about different ways of extracting cosmological information, and forecasts for the near future. I will focus on analytic and numerical modeling on the Epoch of Reionization (EoR) and discuss some of the unique statistical features imprinted into the 21 cm background by extended reionized regions.

Mar. 31, Monday 12:10 pm (TAC Seminar)
Kristen Menou, Columbia
544 Campbell
"Cosmological Physics with Black Holes"
The gravitational observatory LISA will detect coalescing pairs of massive black holes, accurately measure their luminosity distance and help identify a host galaxy or an electromagnetic counterpart. I will describe observational strategies focused on identifying such electromagnetic counterparts and associated host galaxies. Successful identifications would enable a novel type of astrophysical studies and new fundamental tests of gravitational physics on cosmological scales.

Mar. 31, Monday 2:30 pm (Particle Seminar)
Rachel Bean, Cornell
402 Old LeConte
"Observing Inflation Beyond Slow-Roll"

Feb. 4, Monday 4:30 pm (Physics Colloquium)
Reinhard Genzel, Berkeley
1 LeConte
"Massive Black Holes"
Evidence has been accumulating for several decades that many galaxies harbor central mass concentrations that may be in the form of black holes with masses between a few million to a few billion time the mass of the Sun. I will discuss measurements over the last decade, employing adaptive optics imaging and spectroscopy on large ground-based telescopes that prove the existence of such a massive black hole in the center of our Milky Way beyond any reasonable doubt. These data also provide key insights into its properties and environment. I will also briefly discuss the cosmological evolution of massive black holes.

Feb. 5, Tuesday 1:10 pm
Roderik Overzier, MPA
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
" Living fossils: A detailed view of distant Lyman break galaxies using a sample of local analogs"
We have used the Galaxy Evolution Explorer (GALEX) UV imaging survey to show that there exists a rare population of nearby compact UV-luminous galaxies (UVLGs) that closely resembles high redshift Lyman break galaxies (LBGs). These ``living fossils'' are providing us with many details of the properties of starburst galaxies at high redshift. Faint tidal features or companions can be seen in all of the rest-frame optical images, and the UV/optical light is dominated by unresolved (~100-300 pc) ``super starburst regions''. These remarkable structural features revealed by our HST images occur on very small physical scales and are thus not detectable in images of high redshift LBGs, except in a few cases where they are magnified by gravitational lensing. I will discuss the main implications of our new findings in a cosmological context.

Feb. 7, Thursday 4:10 pm (Astronomy Colloquium)
Kartik Sheth, Caltech
2 LeConte
"The Redshift Evolution of Galactic Structures (Bars, Bulges & Disks) at z < 1 from COSMOS: Quantifying the Assembly of the Hubble Sequence"
We have analyzed the redshift-dependent fraction of galactic bars over 0.2

Feb. 12, Tuesday 1:10 pm
Lam Hui, Columbia
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Standard Candle, Standard Yardstick and Non-standard Gravity"
I will discuss four topics: (1) how correlated peculiar flows constitute a surprisingly important source of error for supernova cosmology, (2) how gravitational lensing introduces an observable anisotropy to the galaxy correlation function, and how it impacts baryon acoustic oscillation measurements, (3) how large scale structure data already put interesting constraints on theories of modified gravity, in particular ruling out the popular DGP model at the 3 sigma level, (4) how viable gravity models can be constructed which exhibit a see-saw behavior: a large cosmological constant yielding a small Hubble constant.

Feb. 14, Thursday 11 am
Cristiano Galbiati, Princeton
324 Old LeConte
"Prospects for Direct Dark Matter Searches with Liquid Argon"
Direct searches for WIMP Dark Matter are se poised for a quantum leap in sensitivty. The new generation of liquid noble gas detectors promises to increase the sensitivity of direct dark matter searches by many orders of magnitude in the next five years. I will discuss recent results with a 3-kg detector and prospects of the WARP 150-kg liquid argon currently under construction at Gran Sasso.
I will also report on the recent discovery of the Princeton group of a first source of underground argon depleted in the cosmogenic 39Ar. This discovery opens a possibility for the construction of multi-ton argon-based detectors, capable of exploring a very broad range of WIMP Dark Matter candidates suggested by SUSY theories, with sensitivity to the WIMP-nucleon cross section extending below 10^-10 pbarn and sensitivity for the WIMP mass up to many TeV's.

Feb. 14, Thursday 4 pm (RPM)
Christof Wetterich, Heidelberg
LBL 50A-5132
"Dark Energy- A Cosmic Mystery"
Dark energy - a homogeneously distributed cosmic energy density - seems to explain various cosmological observations. The anisotropies in the microwave background radiation, the formation of structure and the late time acceleration of the Hubble expansion fit into a consistent picture. We discuss quintessence - a dynamical form of dark energy and possible signatures distinctive from a cosmological constant. Particular emphasis is paid to the possible presence of Early Dark Energy and on an explanation why Dark Energy becomes important in a recent cosmological epoch. Quintessence could be related to a new "fundamental" macroscopic force and induce a small time variation of fundamental constants.

Feb. 19, Tuesday 1:10 pm
Linda Tacconi, MPE
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"The Dynamical Properties of Submm Galaxies"
We discuss the results from sub-arcsecond resolution IRAM PdBI millimeter CO interferometry of a small sample of extremely luminous, dusty z~2 submillimeter galaxies (SMGs). These data reveal spatially resolved CO gas kinematics in the observed SMGs, and provide compelling evidence that these SMGs represent extreme, short-lived maximum star forming events in highly dissipative mergers of gas rich galaxies. The resulting high mass surface and volume densities of SMGs are similar to those of compact quiescent galaxies in the same redshift range, and much higher than those in local spheroids. From the ratio of the comoving volume densities of SMGs and quiescent galaxies in the same mass and redshift ranges, and from the comparison of gas exhaustion time scales and stellar ages, we estimate that the SMG phase duration is about 100 Myrs. We compare these results with the dynamical properties of other redshift ~2 galaxy populations, and finally discuss the potential of deriving the molecular gas properties of less luminous, star forming galaxies at redshift 2-3.

Feb. 26, Tuesday 1:10 pm
Dan Stern, JPL/Caltech
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Cosmic Clocks: Constraining the Equation of State of Dark Energy"
The nature of the physics driving cosmic acceleration is perhaps the biggest question facing physics today. Huge resources and large collaborations are now being amassed to determine the dark energy equation-of-state parameter, w. The avenues that are now receiving the most attention are supernova searches, weak lensing, baryon acoustic oscillations, and cluster counts. However, none of these will be free from systematics, and it is still not clear which is the most promising approach. Most likely, multiple approaches will be required, and new ideas still need to be explored. One novel suggestion, proposed theoretically by Jimenez & Loeb (2002), is to measure the relative ages of the red envelope of cluster galaxies, essentially using them as cosmic chronometers or standard clocks. This probe is particularly sensitive to the variation of w as a function of redshift. I will discuss the astrophysical underpinnings to this approach, results obtained using public spectra from the SDSS, and more recent data obtained from Keck. Although the new technique faces challenges from astrophysical uncertainties, these are not necessarily any more daunting than those associated with the other techniques.

Feb. 26, Tuesday 4 pm (RPM)
Shirley Ho, Princeton
LBL 50A-5132
"Small Scale CMB: First Glimpse and Prospects from Atacama CosmologyTelescope"
The observations of Cosmic Microwave Background have played an important role in revolutionizing our understanding of the Universe. They do not only allow us in probing the beginning, the age and the geometry of the Universe, but also enable us to understand the contents of the Universe. The Atacama Cosmology Telescope (ACT), is a new microwave telescope built in the Atacama desert in Chile which commenced observations in November 2007. By combining ACT observations with multiwavelength observations such as the Sloan Digital Sky Survey and Blanco Cosmology Survey, we will probe not only the physics of the early universe, but also the process of growth and assembly of galaxies and large scale structure. I will not only give an update on status of ACT, but also describe the science prospects of the measurements combining with multiwavelength observations.

Feb. 28, Thursday 4:10 pm (Astronomy Colloquium)
Judd Bowman, CalTech
1 LeConte Hall
"First Light" from New Probes of the Dark Ages and Reionization
The application of redshifted 21 cm emission from neutral hydrogen in the high-redshift intergalactic medium (IGM) to probe reionization and the early universe is transitioning rapidly from the realm of theory to practice. The Murchison Widefield Array (MWA) deployed its first 32 antenna tiles in November, 2007, followed by a "first light" demonstration in December. By the end of 2008, all 512 antenna tiles will be deployed and primary science observations will follow in 2009 and 2010.
Another, very different, approach to extracting information from the redshifted 21 cm signal is to directly constrain the global (mean) brightness temperature as a function of redshift. The Experiment to Detect the Global EOR Signature (EDGES) has been designed for this purpose (and is small enough to fit in your suitcase!). EDGES saw its "first light" at the end of the 2006.
In this talk, I will report on the status and preliminary findings of the initial MWA and EDGES deployments. These efforts, combined with recent developments in theoretical modeling and analysis techniques, are establishing a robust prediction of the reionization science possible with radio experiments. I will review the latest expectations -- now grounded with real hardware experiences -- and highlight the implications for the coming years.

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January 2008:

Jan. 15, Tuesday 1:10 pm
Stefan Hilbert, Garching
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
Ray-tracing through the Millennium Simulation
Gravitational lensing is playing an increasingly important role in astrophysics and cosmology. In collaboration with people from MPA and Bonn, I investigate gravitational lensing by carrying out ray-tracing through the Millennium Simulation, one of the largest simulations of cosmic structure formation. In this talk, I will present results for the statistics of strong lensing. Furthermore, I will talk about our efforts towards realistic simulations of weak galaxy-galaxy lensing and cosmic shear surveys. Finally, I will discuss the potential capabilities of future radio telescopes for imaging the cosmic matter distribution.

Jan. 16-18, Wed through Fri
Davis Fest

Jan. 18, Friday 12 noon (INPA Journal Club)
Anton Tikhonov, St. Petersburg
LBL Bldg. 50, room 5026 (the INPA common room)
"Voids in the Local Volume galaxy sample and in high resolution simulations: Limit on appearance of a galaxy in a Dark Matter halo"
Current explanation of the overabundance of dark matter subhalo in the Local Group (LG) indicates that there maybe a limit on mass of a halo, which can host a galaxy. This idea can be tested using voids in the distribution of galaxies: at some level small voids should not contain any (even dwarf) galaxies. We use observational samples complete to M_B=-12 with distances less than 8 Mpc to construct the void function (VF): the distribution of sizes of voids empty of any galaxies. There are ~30 voids with sizes ranging from 1 to 5 Mpc. We also study the distribution of dark matter halos in very high resolution simulations of the LCDM model. The theoretical VF matches the observations remarkably well only if we use halos with circular velocities larger than 30-40 km/s. This agrees with the Local Group predictions. Small voids look quite similar to their giant cousins: the density has a minimum at the center of a void and it increases as we get closer to the border. Thus, both the Local Group data and the nearby voids indicate that isolated halos below ~30 km/s must not host galaxies and that small (few Mpc) voids are truly dark. Luminosity function of Local Volume complete sample is well fitted by Schechter approximation of the average luminosity function of galaxies in the B-band in the Universe but there is an excess of very bright galaxi in the LV that gives luminosity overdensity ~0.5 in K-band (that can be directly convertedto overdensity of stellar mass) with respect to the mean in the local Universe.

Jan. 22, Tuesday
RPM talk at 4

Jan. 22, Tuesday 4 pm (RPM)
Catherine Heymans, UBC
LBL 50A-5132
"Mass, gas and galaxies in the Abell 901/902 supercluster"
I will present a high resolution dark matter reconstruction of the z=0.165 Abell 901/902 supercluster from a weak lensing analysis of the STAGES HST survey. The dark matter map shows the four main structures of the supercluster resolved at high significance, allowing us to detect substructure within and between the clusters. I will show how the distribution of dark matter is well traced by the cluster galaxies, with the brightest cluster galaxies marking out the strongest peaks in the dark matter distribution. I will also compare the dark matter distribution to the hot gas in the cluster, showing a significant extension of the dark matter distribution of Abell 901a in the direction of an infalling X-ray group. Comparing this space-based lensing analysis with an earlier ground-based lensing analysis of the supercluster demonstrates the great importance of space-based imaging for future weak lensing dark matter 'observations'.

Jan. 25, Friday 12:10 pm
Celine Eminian, Sussex
"Physical interpretation of the near-infrared colours of low redshift galaxies"
Near-IR colors of galaxies are poorly understood. I will discuss empirical techniques to interpret the near-IR colours of a sample of 1500 galaxies drawn from SDSS with YJHK photometry from UKIDSS Survey. We study correlations between colors of these galaxies and physical parameters derived from the spectra including specific star formation rate, stellar age, metallicity and dust attenuation. A surprisingly strong correlation is found between the near-IR colors of star-forming galaxies and their dust attenuation. We suggest that this correlation arises because Thermally Pulsing Asymptotic Giant Branch (TP-AGB) stars, which dominate the H and K-band light, are the main source of dust in the galaxies. Finally, I will compare the near-IR colours of the galaxies in our sample to the predictions of three different stellar population models: the Bruzual & Charlot 2003 model, a preliminary version of a new model under development by Charlot & Bruzual, which includes a new prescription for AGB star evolution, and the Maraston 2005 model.

Jan. 28, Monday 3:10 pm (RAL seminar)
Bob Becker, UCD/LLNL
544 Campbell Hall
"The FIRST SURVEY is Gone (from the schedule), but Not Forgotten"
After ten years, it is finally over. With over 800,000 distinct, cataloged sources, the FIRST survey stands as one of the premier archival records of the radio sky. The FIRST collaboration is now switching gears from surveying to mining. I will present some recent results on quasars based on combining the FIRST survey with data from other benchmark surveys such as 2MASS and SDSS. In particular, I will report on investigations into red quasars, FR2 quasars, and submJy radio AGN.

Jan. 28, Monday 4:30 pm (Physics Colloquium)
Wick Haxton, Washington
1 LeConte
"Solar Neutrinos: Old Questions About Hydrogen-Burning Stars"
I will describe progress made in solar neutrino physics over the past three decades, including the new opportunities to use neutrinos to probe physics beyond the standard model. But is the astrophysics end of this story - the question of whether we understand the internal workings of the sun - finished? I will argue the answer is perhaps no, pointing to the CNO neutrinos as one interesting possibility for probing primordial conditions relevant to the general theory of main-sequence stellar evolution.

Jan. 29, Tuesday
RPM Thursday

Jan. 31, Thursday 4 pm (RPM)
Ben Koester, U. Chicago
LBL 50A-5132
"The Average Properties of Galaxy Clusters from MaxBCG-SDSS"
As observational tracers of the most massive structures in the Universe, clusters of galaxies are a key component of many present and future astrophysical experiments. The combination of greater than 10,000 MaxBCG clusters and the Sloan Digital Sky Survey (SDSS) has enabled robust measurements of the average properties of galaxy clusters, as well as the development of a framework for designing future experiments. In this talk, I describe recent results derived from the SDSS and the MaxBCG catalog, including dynamical cluster masses, lensing and x-ray derived masses, measurements of the average properties of cluster galaxies, and cosmological constraints.

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December 2007:

Dec. 4, Tuesday 1:10 pm
Yen-Ting Lin, Princeton
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Fundamental properties of cluster galaxies and their redshift evolution"
Galaxy clusters represent an excellent laboratory for understanding various processes involving the galaxies, the dark matter potential, and the hot intracluster medium. Furthermore, in light of the on-going large scale cluster surveys (e.g. ACT, APEX, SPT), it is of critical importance that we understand the evolution of clusters towards z~1.

I will present a detailed analysis of several fundamental properties (spatial distribution, luminosity function, mass-observable scaling relations) for various classes of cluster galaxies, including the blue and red galaxies, AGNs, and brightest cluster galaxies, based on large samples of clusters at z<0.2. In particular, the relevance of these observations to the halo occupation distribution formalism, the evolution of cluster galaxies, and the environmental dependence of the radio-loud AGN phenomenon, will be discussed. Finally, the redshift evolution of the cluster galaxy population out to z=0.9 is studied in terms of the luminous red galaxies, as well as the scaling relations.

Dec 7, Friday 12 noon (INPA Journal Club)
Don Backer, Berkeley
LBL Bldg. 50, room 5026 (the INPA common room)
"Progress with PAPER: Precision Array to Probe the Epoch of Reionization"
The first stars in the Universe ionize bubbles in the intergalactic medium and heat the surrounding hydrogen that then glows in the 21cm line. We seek to observe the spatial and frequency structure of this emission in the redshift range 7-11, which is frequencies around 150 MHz, via a power spectrum analysis a la COBE. This detection would stimulate more powerful instruments that could chart the early growth of complexity as the Universe emerges out of the Dark Ages through the Epoch of Reionization and into the Galaxy era. Our experiment is taking a step-by-step approach to the many technical challenges in making this measurement. Our instrument, PAPER, has been deployed at a test site in Green Bank, West Virginia (PGB) and, this past July in the outback of Western Australia (PWA), where terrestrial interference is minimal. Early analysis of the Australia data has led to a confusion-limited "all" sky map that has ~1 K level noise in quiet parts of the sky. This is 3 orders of magnitude above the 1 mK we need to achieve to detect the level of signals predicted by Zahn and others. Our early deployments have been with 2-8 dipoles. A 16-dipole array is now being deployed in GB; a 32-dipole array is planned for 2008 in WA. An NSF proposal for a 128-dipole array is pending.

Dec. 10, Monday 3:10 pm (RAL seminar)
David Wilner, CfA
544 Campbell Hall
"Evidence for a population of high redshift submillimeter galaxies"
âtraluminous infrared galaxies are rare in the local universe but may well dominate the total bolometric emission from star formation at high redshifts. Recently, we used the Submillimeter Array to observe a flux limited sample of seven "submillimeter galaxies" in the COSMOS field, selected by the AzTEC camera on the JCMT at 1.1 millimeters. All of these sources-- two radio-bright and five radio-dim-- are detected at 870 microns as single unresolved (<1.2 arcsec) sources, with astrometric accuracy of 0.2 arcsec. These accurate positions allow counterpart identification at other wavelengths in the rich COSMOS data archive. As compared to the two radio bright sources in he sample and to those in previous studies, the five radio dim sources in the sample have (1) systematically higher submillimeter to radio flux ratios, (2) lower IRAC 3.6-8.0 micron fluxes, and (3) no detections at 24 microns. These properties, combined with size constraints, suggest that the radio-dim submillimeter galaxies represent a population of very dusty starbursts, with physical scales similar to local far-infrared bright galaxies, with redshifts higher han radio-bright sources (z > 3).

Dec. 11, Tuesday 1:10 pm
James Bullock , Irvine
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Dark Halo Mergers and Disk Survival"
Milky Way-type dark matter halos are predicted to form primarily from mergers with smaller systems. I will present merger history statistics for galaxy dark matter halos as derived from LCDM cosmological simulations and show that ~95% of Galaxy-size halos experience at least one merger with a system more massive than the Milky Way disk over their histories. I will present simulations aimed at understanding disk response to the types of merger histories expected and speculate on how disk galaxies may form and survive violent merger histories of this kind.

Dec. 14, Friday 12 noon
Michael Schneider, Davis
LBL 50-5026 (INPA journal club)
"Control of systematic errors in obtaining dark energy constraints from galaxy and weak lensing surveys"
While optical imaging surveys are potentially powerful probes of dark energy, their effectiveness depends critically on the control of a number of systematic errors. I will describe tools and techniques we have developed for mitigating several sources of error in future galaxy clustering and cosmic shear surveys. In particular, we have proposed a method to calibrate photometric redshift errors using the cross-correlation of galaxies at different inferred redshifts and are developing improved shear power spectrum estimators and statistical models of the non-linearly evolved mass-density field with the goal of obtaining unbiased and accurate parameter constraints. The latter work makes use of a new statistical framework for using limited numbers of N-body simulations to build a model for the sample variance distribution of the nonlinear matter power spectrum. The performance of these tools with preliminary models is promising and a demonstration using the Deep Lens Survey data is in the works.

Dec. 17, Monday 12:10 pm
Crystal Martin, UCSB
544 Campbell Hall
"Starburst Winds"
For some time now, we have seen overwhelming evidence that supernovae explosions in starburst galaxies drive significant amounts of metals out of galactic disks. The difficult question has been determining how far away from a galaxy these metals go. I will present new measurements of the size (and size evolution) of metal-enriched regions in the IGM and discuss their relation to starburst winds. I will attempt to synthesize these results with our direct knowledge of the wind dynamics in local starburst galaxies.

Dec. 18, Tuesday 1:10 pm
Neelima Sehgal, Rutgers
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Measuring the Growth of Structure with Multi-Wavelength Surveys of Galaxy Clusters"
Current and near-future galaxy cluster surveys at a variety of wavelengths may provide a promising way to obtain precision measurements of structure growth over cosmic time. This in turn would serve as an important precision probe of cosmology. However, to realize the full potential of these surveys, systematic uncertainties in cluster mass estimates and sample selection must be well understood. This work follows two different approaches to understand these uncertainties. 1.) X-ray and weak-lensing mass estimates are compared for shear-selected galaxy clusters in the Deep Lens Survey (DLS) to study possible biases in using cluster baryons or weak-lensing shear as tracers of the cluster dark matter. Results are presented for four galaxy clusters that comprise the top-ranked shear-selected system in the DLS. 2.) Cluster sample selection is investigated in the context of upcoming arcminute-resolution millimeter-wavelength surveys. Large- area, realistic simulations of the microwave sky are constructed and cluster detection is simulated using a multi-frequency Wiener filter to separate the galaxy clusters, via their Sunyaev-Zel'dovich (SZ) signals, from other contaminating microwave signals.

Dec. 19, Wednesday 4 pm (RPM)
Shirley Ho, Princeton
LBL 50A-5132
"Next Frontiers of CMB Research"
The Cosmic Microwave Background (CMB) has been providing us with a wealth of information for cosmology. Can we learn more from the CMB apart from its primary anisotropies? I shall present the next frontiers of CMB research: the Integrated Sachs-Wolfe (ISW) effect, Weak Lensing of the CMB (WL of CMB) and Kinetic Sunyaev-Zeldovich (kSZ) effect. In order to understand the gravitational potential (and thus cosmological parameters such as dark energy and curvature) of the Universe, we study the ISW effect and weak lensing of the CMB using the following datasets: WMAP, 2MASS, SDSS LRGs and Quasars, and NVSS. We perform a joint analysis of all samples, allowing a reliable covariance matrix to be constructed - including all the cross-correlations of different samples, which is necessary for joint cosmological parameter fitting. I present results from the first likelihood analysis of ISW and WL of CMB, that allows all cosmological parameters to vary. This also places cosmological constraints on parameters of the Universe such as curvature and dark energy equation of state. I will also discuss the prospects of using the kSZ effect as the first tool for systematically mapping the baryon density of the Universe. More specifically, I will present predictions for various on-going and upcoming surveys such as ADEPT with ACT/SPT/APEX and SDSS with PLANCK.

Dec. 20, Thursday 4 pm (RPM)
Joe Silk, Oxford
LBL 50A-5132
"Dark Matters"
One of the greatest mysteries in the cosmos is that it is mostly dark. That is, not only is the night sky dark, but also most of the matter in the universe is dark. For every atom visible in planets, stars and galaxies today, there exists at least five or six times as much weakly interacting ``Dark Matter'' in the universe. I will review the various signatures of dark matter, and discuss prospects for its detection.

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November 2007:

Nov. 2, Friday 12 noon (INPA Journal Club)
David Rapetti, SLAC
LBL Bldg. 50, room 5026 (the INPA common room)
"New contraints on dark energy from X-ray galaxy cluster studies"
Most of the energy density of the Universe appears to be in the form of dark matter and dark energy, and yet these two components are the most intriguing mysteries in current cosmology. Using two complementary X-ray galaxy cluster studies we present new constraints on the mean matter density of the Universe, dark energy density, normalization of the density fluctuation power spectrum, and dark energy equation of state. First, using Chandra measurements of the X-ray gas mass fraction in 42 hot, X-ray luminous, dynamically relaxed galaxy clusters spanning the redshift range 0.05

Nov. 2, Friday 12:30 -5pm
Galaxy/Cosmo theory meeting
Campbell Hall 2nd floor, Dean's Office Conference Room

Nov 5, Monday 12:10 pm (TAC seminar)
Robyn Levine, Colorado
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"From Megaparsecs to Milliparsecs: Modeling a Disk Galaxy with Cosmological Simulations"
Using a hydrodynamic adaptive mesh refinement code, we simulate the growth and evolution of a disk galaxy hosting a supermassive black hole within a cosmological volume. Reaching a dynamical range in excess of 10 million, the simulation follows the transport of gas from super-galactic scales all the way down to the outer edge of the accretion disk. I will present the results of our study of the circumnuclear region of the simulated galaxy. The self-gravitating, cold, molecular gas disk in this region is globally highly unstable, driving turbulence which maintains the local stability of the disk. The super-sonic turbulence prevents catastrophic star formation in the disk and provides a natural mechanism for angular momentum transport all the way down to sub-pc scales.

Nov. 6, Tuesday 1:10 pm
Simon De Deo , Chicago
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Gas and gravity: new techniques for secondary anisotropies in the CMB"
The "next generation" of CMB observatories will uncover a wealth of detail at smaller scales -- where the primary source of signal comes from matter well after the recombination epoch. I review some of my work in the theory and analysis techniques that will help us extract the most from the surveys, focusing in particular on new methods for the kinetic Sunyaev Zel'dovich effect.

Nov. 7, Wednesday 12:10 pm (theory lunch)
Christoph Pfrommer, CITA 501 Campbell Hall
"Cosmic Rays in Clusters of Galaxies - Tuning in to the Non-Thermal Universe"
Understanding the non-thermal physics connected to structure formation will be an important frontier for cosmology in the upcoming decade, while entering a new era of multi-frequency experiments that soon will go on-line. In this talk, I present theoretical work that complements this observational effort and describe high-resolution simulations of galaxy clusters that self-consistently follow dissipative gas and cosmic ray physics. A substantial pressure contribution from relativistic protons can have a major impact on the properties of the intra-cluster medium and modifies thermal cluster observables such as the X-ray emission and the Sunyaev-Zel'dovich effect. I will review different particle acceleration processes in clusters and put forward a unified model for the generation of cluster radio relics and giant radio halos. The resulting model signatures of the expected radio synchrotron, hard X-ray, and gamma-ray emission can then be tested with the upcoming new generation of low-frequency radio telescopes and gamma-ray instruments such as GLAST.

Nov. 8, Thursday 4 pm (RPM)
Nic Ross, Penn State
LBL 50A-5132
"Clustering of Luminous Red Galaxies, and Applications to Cosmology"
Luminous Red Galaxies (LRGs) have proved to be optimal tracers of large-scale structure. In this talk, I will present results from two recent LRG surveys, the 2dF-SDSS LRG And QSO (2SLAQ) Survey, and the AAOmega LRG Survey, paying particular attention to the dynamical and geometric (Alcock-Paczynski) properties given in the clustering signal of the LRGs. We will then look forward to upcoming galaxy redshift surveys and briefly discuss the observational challenges that will have to be overcome in order to make reliable measurements of cosmological parameters.

Nov. 13, Tuesday 1:10 pm
Sarah Hansen , Chicago
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Galaxy Content of Clusters and Groups in the Local Universe"
I will present recent analysis of SDSS imaging data quantifying the population of galaxies in MaxBCG-identified clusters and groups. I will discuss the distributions of satellite galaxy luminosity and satellite color and the dependence of these on cluster properties. I will also show the relationship of Brightest Cluster Galaxy luminosity to cluster mass and to satellite galaxy luminosity. These measurements of cluster light, in combination with lensing results, also allow measurement of ensemble cluster mass-to-light profiles. This study demonstrates the power of cross-correlation background correction techniques for measuring galaxy populations in purely photometric data, and provides a baseline for the study of galaxy evolution in higher redshift samples.

Nov. 13, Tuesday 4 pm (RPM)
Mark Trodden , Syracuse
LBL 50A-5132
"Interactions and instabilities in cosmology's dark sector"
Theories possessing a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the universe may exhibit an adiabatic regime in which the quintessence field always sits at the minimum of its effective potential, determined by the local dark matter density. I will discuss a generic instability in such situations, arising when If the coupling strength becomes much larger than gravitational. I will demonstrate how this instability occurs, and illustrate it by considering specific coupled CDM and Mass Varying Neutrino (MaVaN) models of dark energy.

Nov. 15, Thursday 12 noon (special INPA talk)
Ryan Foley, UCB
LBL 50-5026
"Constraining Cosmic Evolution of Type Ia Supernovae"
Measurements of high-redshift type Ia supernovae (SNe Ia) have revealed that the expansion of the Universe is accelerating. A decade after this realization, our measurements of the nature of Dark Energy is dominated by systematics associated with supernovae. One such error is possible evolution between low and high-redshift SNe. As part of the ESSENCE survey, spectra of SNe are obtained to determine their type and redshift. A by-product of this effort is a large sample of low to moderate signal-to-noise SN Ia spectra. I present composite spectra of high-redshift SNe (and their low-redshift counterparts) using the cumulative signal of ~100 high-redshift SN spectra to assess small differences between the two samples.

Nov. 15, Thursday 4 pm (RPM)
Josh Frieman, Chicago and FNAL
LBL 50A-5132
"SDSS SN/Dark Energy Survey"
While cosmological observations now point convincingly to an accelerating Universe, we have no fundamental understanding of the physics driving this expansion: is it a new form of stress-energy with negative pressure, e.g., the cosmological constant, or does it signal a breakdown of General Relativity on large scales? A number of observational probes are being applied to this problem---most prominently supernovae, weak lensing, galaxy clusters, and baryon acoustic oscillations---and a series of increasingly ambitious projects have been proposed to attack it over the next decade. This talk will focus on two projects, one on-going, the other near-term. The first is the SDSS Supernova Survey, a 3-year project now in the final stages of data-taking, which has measured multi-band light curves and spectra for several hundred type Ia supernovae at intermediate redshifts. I will discuss the early results and some of their implications for future supernova cosmology studies. The second is the Dark Energy Survey (DES), a large-area, multi-band imaging survey that will use a new wide-field camera on the 4-meter telescope at Cerro Tololo Inter-American Observatory. Covering 5000 square degrees and beginning in 3 years, DES will employ all four of the above dark energy methods.

Nov. 16, Friday 12 noon
Katie Mack , Princeton
LBL 50-5026 (INPA journal club)
"Primordial black holes in the Dark Ages"
I will discuss the effect of evaporating primordial black holes on the ionization history of the universe, with an emphasis on the limits derivable from future 21-cm observations of high-redshift neutral hydrogen.

Nov 20, Tuesday 1:10 pm
Shirley Ho, Princeton
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"The Dark Side and the Bright Side of the Universe"
In order to understand cosmological parameters of the Universe, such as the dark energy equation of state, the curvature of the Universe, we make joint analysis of large scale datasets such as 2MASS, SDSS LRGs, SDSS QSOs, NVSS with WMAP to investigate the Integrated Sachs-Wolfe effect(ISW) and Weak Lensing (WL) of CMB. We explore different cosmological models by using Monte-Carlo Markov Chains combining our detections on ISW and WL of CMB with WMAP.
As the background cosmological parameters are being set, an unavoidable question arises: how does these ''star stuff'' evolve in the Universe? I would like to discuss a few of these questions:

1. How do we relate the galaxies to the dark matter halos?
2. How long does it take for galaxies to merge?
3. Where are the missing baryons?
4. What are the energy inputs from the quasars to the surrounding medium of the galaxies?

Results and/or novel methods will be presented to these questions.

Nov 26, Monday 12:10 pm (TAC seminar)
Phil Hopkins, Harvard
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"The Role and Evidence of Dissipation in the Formation of Elliptical Galaxies"
Recent observations suggest that elliptical galaxies can be divided into two broad classes: those with central "cusps" in their surface brightness profiles, and those with central "cores." The "cusp" class dominates the population at intermediate and lower luminosities, where ellipticals are also observed to be much more dense than spiral galaxies of the same mass. This discrepancy has presented a long- standing challenge for the "merger hypothesis", that ellipticals formed from the merger of disk galaxies, and the formation of new stars in a dissipational starburst has generally been postulated as the means to reconcile the observations. By combining new generations of numerical simulations of gas-rich disk-disk mergers and observations of the nuclei of elliptical galaxies, we show that these "cusps" preserve a memory of the merger history of elliptical galaxies, and can be used to reconstruct the role of dissipation in the formation of ellipticals even after a Hubble time of subsequent evolution.

Nov. 26, Monday 4:30 pm (Physics Colloquium)
Andrei Linde, Stanford
1 LeConte
"Inflation and String Cosmology"
I will give a brief review of inflationary cosmology and describe recent progress based on string theory with stabilized internal dimensions. These developments lead to a different outlook on inflationary theory, on the theory of dark energy, and on the possibility to discover gravitational waves produced during inflation. I will also discuss string theory landscape and the probability measure in eternal inflation.

Nov. 27, Tuesday 1:10 pm
Louie Strigari, Irvine
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Dark matter, small-scale structure, and dwarf galaxies"
The standard model of cold dark matter (CDM) predicts the existence of thousands of small dark matter halos orbiting the Milky Way, and steep cusps in the central regions of dark matter halos. The low-luminosity, dark matter dominated dwarf satellite galaxies of the Milky Way provide an ideal laboratory to test these predictions, and place strong constraints on the nature of dark matter. I will discuss the extent to which the discovery of new dwarf satellites by the SDSS can test solutions to the CDM ``missing satellites problem," and how future astrometric data from the most luminous satellites will reveal the presence of dark matter cores or cusps. I will also discuss prospects for detecting gamma-rays from annihilating dark matter in the Milky Way, and how the cosmological gamma-ray background can be generally used to search for signals from alternative dark matter.

Nov. 28, Wednesday 12:30 pm, (Particle Theory Seminar)
Cedric Pahud, Sussex
LBNL 50-5026
"The inflaton as dark matter"

Nov. 29, Thursday 1:30 pm
Molly Swanson, MIT
LBL 50B-4205
"Using Galaxies as Cosmic Tracers"
A widely used cosmic mapping technique is to use galaxies as tracers of the underlying cosmic matter distribution. I will address some of the challenges of this method with SDSS measurements of galaxy bias that quantify its stochasticity and its dependence on scale, luminosity, and color. I will also present new tools I have developed for the MANGLE software package for managing angular masks of next-generation galaxy surveys and other cartographic applications that have recently been made publicly available.

Nov. 29, Thursday 4:00 pm
Richard Cool, Arizona
LBL 50B-5132
"Constraining the Evolution of the Most Massive Galaxies Since z~1"
The popular model for the formation of early-type galaxies is the hierarchical merging scenario. However, the details and frequency of merging are not yet known, particularly in dense environments. The high-mass end of the galaxy luminosity function, as the extreme example of the merger phenomenon, is the most sensitive to various merger model assumptions and thus provides an ideal testing ground for these models. I will present recent work utilizing wide-area spectroscopic surveys to place constraints on the star formation and merger histories of the most massive galaxies in the universe since z~1. In particular, I will show that massive red-sequence galaxies have had very little star formation since z~1, thus limiting the importance of gas-rich mergers since that epoch, and show that the number density of very massive galaxies has evolved little in that same epoch, suggesting that very massive galaxies assembled their stellar mass at z>1. I will close with a brief introduction of PRIMUS, a new spectoscopic survey aimed at observing 15 square degrees of the southern sky with high-quality archival optical, infrared, and X-ray data and obtaining 300,000 galaxy redshifts to z~1. PRIMUS will be the largest intermediate-redshift galaxy survey to date as well as the largest sample of Spitzer-detected objects and will allow for a broad-range of investigations.

Nov. 30, Friday 12:00 pm, (INPA Seminar)
Robert Quimby, Caltech
LBNL 50-5026 (INPA conference room)
"Big and Bright: Two Discoveries from the Texas Supernova Search"
Supernovae, the cosmic fireworks accompanying the catastrophic ends of some stars, have been the highly scrutinized subjects of multiple research consortia for decades. It is therefore initially surprising to learn that the most luminous and, in some sense, most obvious supernovae have only recently been found--and they were done so by one of the smallest telescopes competing in the field. In this talk I will review the Texas Supernova Search and our two most famous discoveries: SNe 2006gy and 2005ap. I will present the remarkable observations and a few of the theoretical models formulated to offer explanation. SN 2006gy is most likely an explosion from an exceptionally massive star and it is the first observed supernova for which a pair instability trigger must be considered. 2005ap, the most luminous supernova yet identified, may be a distinctly different phenomena, one perhaps related to gamma-ray bursts. I discuss possible reasons as to why such supernovae have yet to be found by other surveys.

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October 2007:

Oct. 2, Tuesday 1:10 pm
Peng Oh, UCSB
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Signatures of Heating in the Intergalactic and Intracluster medium"
I discuss observational signatures and physical consequences of heating in the intergalactic medium during hydrogen and helium reionization, and cosmic-ray heating in the intracluster medium.

Oct. 4, Thursday 4:00 pm (Astronomy Colloquium)
Darren Croton, UCB
2 LeConte
"What *don't* we know about galaxy formation?"
Amazing progress has been made in recent years in our understanding of galaxies and their evolution, thanks in large part to the quality of galaxy surveys at low and high redshift (e.g. 2dFGRS, SDSS, COSMOS, DEEP2, VVDS, ...). However, the focus of *next* generation surveys (e.g. DES, PanSTARRS, LSST, ...) is not primarily galaxy formation, but rather dark energy. Although "w" is certainly important for cosmology and will be measured, I will argue (perhaps controversially) that the bulk of the science from these "successor" surveys will NOT be dark energy related. Instead, most of their science will continue the current focus of unravelling of galaxy evolution, and this will continue well into the next decade.

Oct. 9, Tuesday 1:10 pm
Anze Slosar , Berkeley
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Locomotion in the Zoo"
In this talk I will discuss two disjoint, but equally interesting topics. First, I will talk about peculiar velocities of nearby supernovae. Coherent velocity flows introduce coherent perturbations to the apparent luminosities of nearby supernovae. This effect has recently been detected at high statistical significance. I will discuss present and future constraints on sigma8, effect on Hubble diagram measurements and potential systematic effects. Second, I will talk about Galaxy Zoo, a project that attempts to harness the power of Internet public to classify galaxies from the SDSS catalogue. In a couple of months the project has achieved over 30 million classifications from about 100 thousand users. I will discuss unique challenges of reducing this dataset and some preliminary results.

Oct. 10, Tuesday 12:10 pm (Theory lunch)
Oliver Zahn , Berkeley
501 Campbell Hall
"Gravitational lensing of the CMB: theory, detection, and future applications"
Light from our most distant source is deflected on its way past large scale structure, and the statistical properties of the final displacement field on the sky can be used to confirm our cosmological paradigm, and measure cosmological parameters. I will outline the basics of CMB lensing, talk about the recent detection in cross correlation with a radio galaxy survey, and elaborate on the future potential of this cosmological probe, with focus on efforts going on here at Berkeley. The observable promises new insight into the evolution of dark energy, tightened constraints on the neutrino mass scale, and it will also play an important role in our quest for detecting primordial gravity waves, the smoking gun of inflation.

Oct. 11, Thursday 4:00 pm (Astronomy Colloquium)
David Weinberg, OSU
2 LeConte
"Galaxies and Dark Matter"
I will discuss various aspects of the relation between galaxies and dark matter and more general issues in the theory of galaxy formation, including: disk galaxy scaling relations and the fraction of baryons in galaxies, the relation between satellite galaxies and dark matter substructures, the universality of the relation between central galaxies and dark matter halos, the relative accretion/merger rates of central and satellite galaxies, and the origin of bimodality in the galaxy color distribution and the shape of the galaxy luminosity function. While recent theoretical and observational developments have shed light on many of these issues, many puzzles remain.

Oct. 16, Tuesday 1:10 pm
Jason Prochaska , UCSC
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Studies of the ISM and IGM of the z>2 Universe with GRB Afterglow Spectroscopy"
I will discuss several results related to spectroscopic observations of bright GRB afterglows. These data constrain the physical conditions of gas near star-forming regions in high z galaxies, reveal the nature of galactic velocity fields, and probe the intergalactic medium in a fashion complimentary to quasar absorption line studies. I will introduce the techniques, and highlight current (startling) results.

Oct. 17, Wednesday 12:10 pm (Theory Lunch)
Anze Slosar , UCB
501 Campbell Hall
Sterile neutrinos as a dark matter candidate

Oct. 18, Thursday 4 pm (RPM)
Uros Seljak, Zurich
LBL 50B-4205
"Different paths to dark energy"
I will review some of the most promising paths to measure dark energy and its properties such as its density, redshift evolution, equation of state, its clustering properties etc. Among the techniques I will discuss are weak lensing, galaxy clustering, galaxy clusters, supernovae and others. I will argue that a combined approach of several methods holds most promise to uncover the mystery of dark energy.

Oct. 23, Tuesday 1:10 pm
Tristan Smith, Caltech
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
Local gravity and the cosmos: using local tests of modified gravity to probe cosmological physics"
We have two strong reasons to argue that Einstein's theory of general relativity may be incomplete. First, given that it cannot be expressed within a consistent quantum field theory there is reason to expect higher energy corrections. Second, the observation that we are undergoing a current epoch of accelerated expansion might indicate that our understanding of gravity breaks down at the largest scales. A generic result of modified gravity is the creation of a new degree of freedom within the gravitational sector. This new degree of freedom then generically connects local physics to cosmological dynamics. I will present the results of studying two modified theories of gravity emphasizing how they bridge the gap between local and cosmological physics. First I will discuss work I have done on f(R) modified gravity theories, delineating under what conditions these theories deviate strongly from general relativity. Using these results I will talk about some recent work on attempting to detect a characteristic signature of these theories from gravitational lensing. Second I will discuss recent results on ways we may test Chern-Simons gravity (a result of the low energy effective string action) in the Solar System. Chern-Simons gravity has been identified as a candidate for leptogenesis as well as a source for circularly polarized gravitational-waves from inflation. As I will discuss, constraints on Chern-Simons gravity may improve in the near future with further observations of double pulsar systems.

Oct. 24, Wednesday 12:30 pm, (Particle Theory Seminar)
Daniel Cumberbatch, Oxford
LBNL 50-5026
"Sterile neutrinos as subdominant warm dark matter"
In light of recent findings which seem to disfavour a scenario with warm dark matter entirely constituted of sterile neutrinos produced via the Dodelson-Widrow (DW) mechanism, we investigate the constraints attainable on this mechanism when relaxing the usual hypothesis that the relic neutrino abundance must necessarily account for all of the dark matter. With this purpose we first study how to interpret the limits attainable from X-ray non-detection and Lyman-alpha forest measurements in the case in which sterile neutrinos constitute only a fraction f_s of the total amount of dark matter. Then, assuming that sterile neutrinos are generated in the early Universe solely through the the DW mechanism, we demonstrate how the X-ray and Lyman-alpha results jointly constrain the mass-mixing parameters governing their production. Furthermore, we show how the same data allows us to put a robust upper limit f_s<0.7 at the 2 sigma level, rejecting the case of f_s=1 at approximately the 3 sigma level.

Oct. 25, Thursday 4 pm (RPM)
Julian Borrill and Peter Nugent, LBL/NERSC
LBL 50A-5132
C³: the new Computational Cosmology Center at LBL
In recent years astrophysics has undergone a renaissance, transforming from a data-starved to a data-driven science. A new generation of experiments - including the Planck and JDEM satellite missions - will gather data sets so massive that their analysis requires leading-edge high performance computing resources. Continuing their decade-long collaboration in this field, the Physics and Computational Research Divisions at LBNL have formed the Computational Cosmology Center. C^3 is a focused collaboration of astrophysicists and computational scientists to develop the tools, techniques and technologies to meet the analysis challenges posed by present and future cosmological data sets. We will give an overview of the science driving C^3's current activities, and present some of the highlights of the founding members' recent research.

Oct. 25, Thursday 4:00 pm, (Astronomy Colloquium)
Dan Stern, JPL/Caltech
2 LeConte
"Obscured Quasars at High Redshift"
The dominant sources of energy production in the universe are fusion in stars and gravitational accretion onto supermassive black holes. The tight correlation between nuclear black hole mass and bulge mass implies the processes are intimately connected. However, identifying an unbiased census of black holes in the universe remains challenging, hampering our ability to fully probe this connection. Furthermore, the spectrum of the X-ray background, which is significantly harder than that of bright, optically-selected quasars, requires a large population of heavily-obscured AGN. Only a handful of luminous examples of this population had been identified prior to recent years. Using data from wide-area surveys with the Spitzer Space Telescope and the Chandra X-Ray Observatory, we have recently uncovered a large population of heavily obscured, luminous quasars. I discuss the properties of this population, the relative merits of selection at different wavelengths, and how this population relates to unified models of active galaxies. I will also highlight other exciting science enabled by these wide-area, multi-wavelength surveys, and conclude with future prospects with warm Spitzer surveys and upcoming NASA missions such as WISE and NuSTAR.

Oct. 30, Tuesday 1:10 pm
Jeremy Tinker , Chicago
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Reverse-Engineering Galaxy Formation"
Measurements of galaxy clustering can provide significant insight to the problem of galaxy formation. The major theoretical advance in galaxy bias has been the Halo Occupation Distribution (HOD), which quantifies bias by specifying the distribution of galaxies within dark matter halos. I will show that the HOD can test an important question in galaxy formation-- namely, are the properties of a galaxy determined only by the mass of its host halo, or does large-scale environment play a role? The answer the data provides is that halo mass determines galaxy luminosity, color, and morphology, leaving little to no room for halo environment or formation history.

I will also show new results of applying the halo occupation technique to quasar absorption systems, thereby constraining the cold gas content of halos, the reservoir from which galaxies form their stars. The clustering of MgII absorbers can only be fit with a rapid reduction in the cold gas fraction at M~10^{11.5} Msol/h, the location of the cold-mode/hot-mode transition seen in simulations. The incidence rate must be near unity to account for absorber frequency, implying that MgII absorbers are correlated with all galaxies, not a special subset such as starbursting systems.

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September 2007:

Sep. 6, Thursday 10 am
Joel Primack, UCSC
LBL Building 50 Auditorium
"Report from The Beyond Einstein Program Assessment Committee"
Before 2004, NASA's Beyond Einstein program included ambitious space missions to understand the nature of the dark energy that has been accelerating the expansion of the universe, test general relativity, and discover gravity waves from the mergers of supermassive black holes and from the cosmic inflation that preceded the Big Bang. All of these, plus space missions to map our home galaxy and investigate whether planets around other stars have life, were indefinitely postponed when President Bush decided in January 2004 that NASA's highest priority is to put astronauts back on the moon and eventually send them to Mars. Under pressure from Congress, the National Academy of Sciences was commissioned in 2006 to report on how to restart the Beyond Einstein program. This colloquium by one of the members of this Academy study, released September 5, will summarize and explain the research strategy the report proposes and its implications for continued U.S. participation in the exploration of the universe.

Sep. 6, Thursday 4:00 pm (Astronomy Colloquium)
Andrey Kravtsov, Chicago
2 LeConte
"Cosmological simulations of galaxy clusters: successes, problems, and challenges"
I will describe high-resolution self-consistent cosmological simulations of clusters forming in the concordance Cold Dark Matter model with vacuum energy. The resolution of the simulations is sufficiently high to resolve formation and evolution of cluster galaxies and their impact on cluster gas. We use these simulations to study the effects of galaxy formation on the global properties of clusters, such as the shape of cluster dark matter halo and its density profile, the baryon fractions, gas density and temperature profiles. I will present comparisons of simulations results with the recent X-ray Chandra, Sunyaev-Zeldovich, and optical observations of clusters with highlights of both successes and problems of the models. I will show that despite complexities of their formation and uncertainties in their modeling, clusters of galaxies both in observations and numerical simulations are remarkably regular and consistent outside of their core region (~5% of the virial radius), which holds great promise for their use as cosmological probes.

Sep 7, Friday 12 noon (INPA Journal Club)
Huan Tran, Berkeley
LBL Bldg. 50, room 5026 (the INPA common room)
"Measuring the polarization of the Cosmic Microwave Background; From detection to probing Inflation"
While the spectrum and the temperature have been successfully measured by NASA Satellites, we are just now beginning to characterize the polarization. A high sensitivity map of the polarization will verify one of the major pillars of the gravitational instability induced model of the formation of cosmological structures. Higher sensitivity maps of the polarization will chart out the detailed anisotropies in the sky, and may eventually lead to detection of an extremely faint signal left by primordial gravity waves, left from the era of Inflation.
I will be describing a series of experiments, Maxipol, EBEX, and PolaRbeaR. Maxipol was a joint UC Berkeley-University of Minnesota balloon-borne project that flew in 2003. I will be describing the results and lessons learned from this flight. PolaRbeaR is the next generation in polarization measurements. This ground-based experiment has a 3.5m telescope coupled to a large array of bolometers. EBEX is a long-duration balloon-borne experiment sharing many technological features with PolaRbeaR. These experiments will be fielding in the next few years.

Sep 11, Tuesday 1:10 pm
Richard Cool, Arizona
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Constraining the Evolution of the Most Massive Galaxies Since z~1"
The popular model for the formation of early-type galaxies is the hierarchical merging scenario. However, the details and frequency of merging are not yet known, particularly in dense environments. The high-mass end of the galaxy luminosity function, as the extreme example of the merger phenomenon, is the most sensitive to various merger model assumptions and thus provides an ideal testing ground for these models. I will present recent work utilizing wide-area spectroscopic surveys to place constraints on the star formation and merger histories of the most massive galaxies in the universe since z~1. In particular, I will show that massive red-sequence galaxies have had very little star formation since z~1, thus limiting the importance of gas-rich mergers since that epoch, and show that the number density of very massive galaxies has evolved little in that same epoch, suggesting that very massive galaxies assembled their stellar mass at z>1. I will close with a brief introduction of PRIMUS, a new spectoscopic survey aimed at observing 15 square degrees of the southern sky with high-quality archival optical, infrared, and X-ray data and obtaining 300,000 galaxy redshifts to z~1. PRIMUS will be the largest intermediate-redshift galaxy survey to date as well as the largest sample of Spitzer-detected objects and will allow for a broad-range of investigations.

Sep 18, Tuesday 1:10 pm
Joerg Colberg, Pittsburgh
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Supermassive Black Holes and Their Environments"
We make use of the first high--resolution hydrodynamic simulations of structure formation which self-consistently follows the build up of supermassive black holes (Di Matteo et al., arXiv:0705.2269) to investigate the assembly of black holes and the relations between black holes, host haloes and large--scale environment. We discuss relations between halo and black hole masses, and between the activity of galactic nuclei and black hole and halo masses. We study the environments that contain the highest mass and most active black holes and the environments with the least active black holes, across the full range of available redshifts. We also briefly compare black hole activity with star formation in different environments.

Sep. 20, Thursday 4:00 pm (Astronomy Colloquium)
Joel Primack, UCSC
2 LeConte
"Restarting the Exploration of the Universe"
Before 2004, NASA's Beyond Einstein program included ambitious space missions to understand the nature of the dark energy that has been accelerating the expansion of the universe, test general relativity, and discover gravity waves from the mergers of supermassive black holes and from the cosmic inflation that preceded the Big Bang. All of these, plus space missions to map our home galaxy and investigate whether planets around other stars have life, were indefinitely postponed when President Bush decided in January 2004 that NASA's highest priority is to put astronauts back on the moon and eventually send them to Mars. Under pressure from Congress, the National Academy of Sciences was commissioned in 2006 to report on how to restart the Beyond Einstein program. This colloquium by one of the members of this recently released Academy study will summarize and explain the research strategy the report proposes and its implications for continued U.S. participation in the exploration of the universe.

Sep 25, Tuesday 1:10 pm
Rob Simcoe , MIT
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Galaxy Formation Feedback and the Early Chemical Enrichment of Intergalactic Matter"
Energetic heating from star formation and/or AGN seems to be an important regulating factor in the growth of galaxies, yet this phonemenon is notoriously difficult to observe and characterize. I will describe current measurements of intergalacic chemical abundances at high redshift - both near and far from star forming galaxies - and discuss their relevance for studies of galaxy formation feedback.

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August 2007:

Aug. 3, Friday 12 noon
Daniel Holz, LANL
LBL 50-5026 (INPA journal club)
"Cosmology with Gravitational Waves"
We discuss the use of gravitational wave sources as probes of cosmology. The inspiral and merger of a binary system, such as a pair of black holes or neutron stars, is extraordinarily bright in gravitational waves. By observing such systems it is possible to directly measure an absolute distance to these sources out to very high redshift. When coupled with independent measures of the redshift, these "standard sirens" enable precision estimates of cosmological parameters. We review proposed GW standard sirens for the LIGO and LISA gravitational wave observatories. Percent-level measurements of the Hubble constant and the dark energy equation-of-state may be feasible with these instruments

Aug. 9, Thursday 4 pm
Bob Nichol, Portsmouth
LBL 50A-5132
"Looking for dark energy using the SDSS and other massive sky surveys"
Dark energy has emerged as a serious problem for fundamental physics. I will review the present evidence for this mysterious quantity based on data from the Sloan Digital Sky Survey (SDSS). I will then look forward to the next generation of surveys which will move us from the 'discovery phase' into the 'measurement phase' of dark energy research.

Aug. 29, Wednesday 12:10 pm (Theory lunch)
Avishai Dekel, Hebrew Univ.
501 Campbell Hall
"Long-Term Gravitational Quenching by Clumpy Accretion in Galaxies and Clusters (or Is AGN Feedback Necessary?)"

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July 2007:

July 23, Monday 12:10 pm
Kevin Bundy, Toronto
544 Campbell Hall (also videoconferenced to LBL 50A-5131)
"Understanding Star Formation Downsizing: Testing the Role of Mergers and AGN"
Growing evidence suggests that the evolution of galaxies since the peak in global star formation activity at z~2 proceeds in a mass-dependent fashion. The most massive galaxies mature first while smaller systems appear to complete their evolution later. This "downsizing" pattern is intriguing in the context of the hierarchical Cold Dark Matter framework which suggests that the most massive structures should be the last to evolve. In such scenarios, downsizing likely indicates the presence of poorly understood physical mechanisms that play an important role in driving galaxy evolution and quenching star formation. I will summarize results from Palomar infrared imaging and the DEEP2 Galaxy Redshift Survey that help reveal and quantify the nature of downsizing and shed light on potential physical processes that may explain it. I will then present new work that seeks to test the roles played by two such processes in particular, namely major mergers and AGN feedback.

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June 2007:

June 13, Wednesday 12:30 pm, 4D seminar
Douglas Finkbeiner, Harvard
LBNL 50-5026 (INPA conference room)
"Exciting Dark Matter and the INTEGRAL SPI 511 keV signal"

Cosmology Seminars in Previous Years