October 5, 2005 | 3:30 PM | RI 480 | Wednesday colloquium Simulating Reionization: Yesterday, Today, Tomorrow Nick Gnedin, Fermilab
I will review the current status of modeling of the process of cosmic reionization with numerical simulations. With the rest of numerical cosmology, the study of reionization is going through a revolutionary transition from the first stage of primitive, semi-qualitative simulations to the realistic, quantitative models that can be sensisibly compared to observational data. This transition, when complete, will allow us to model reionization with spatial dynamic range in excess of 10 million. Armed with these new tools, we will be able to reach the next big prize in numerical cosmology - helium reionization.
October 12, 2005 | 3:30 PM | RI 480 | Wednesday colloquium A Cross-correlation Study of Galaxies and QSO Absorption-line Systems Hsiao-Wen Chen, University of Chicago
The forest of absorption line systems observed in the spectra of background QSOs offers a sensitive probe of tenuous gas in extended halos around galaxies as well as in intergalactic medium. Understanding the origin of QSO absorption line systems (QALS) bears directly on our effort to uncover missing baryons and to apply known absorption line statistics to constrain statistical properties of faint galaxies in the distant universe. I will show based on comparisons of galaxies and QSO absorbers along common lines of sight that extended gaseous envelopes are a common and generic feature of galaxies of a wide range of luminosity and morphological type. In addition, I will present a cross-correlation analysis between galaxies and absorbers that yields further constraints on the large-scale distribution of tenuous gas with respect to galaxies. Finally, I will discuss the prospects of studying absorption lines systems identified along the sightlines toward the optical afterglow of gamma-ray bursts.
October 19, 2005 | 3:30 PM | RI 480 | Wednesday colloquium Probing the ISM of High z Galaxies with DLA and GRB Afterglows Jason Prochaska, Lick Observatory, UC Santa Cruz
I will describe new results related to studies of the HI content of damped Lya systems and high resolution spectroscopy of GRB afterglows. The talk will highlight cosmological evolution in neutral gas (measured from the SDSS Data Release 3) and physical properties of gas surrounding star forming regions in high z galaxies.
October 26, 2005 | 3:30 PM | RI 480 | Wednesday colloquium The Swift Gamma-Ray Burst Explorer: Early views into black hole formation David Burows, Penn State
NASA's Swift Gamma-Ray Burst Explorer is designed to localize and study Gamma-Ray Bursts (GRBs) and their afterglows, beginning within a few minutes of the burst events. Swift has now discovered over 75 GRBs and has produced detailed X-ray light curves and spectroscopy on over 60 of these, exceeding in the past nine months the total sample of GRB afterglows found in the previous 8 years. Key findings to date include rapid decays at early times and giant X-ray flares, suggesting that the central engines of GRBs continue long past the end of the prompt gamma-ray emission. We have also localized 3 short GRBs, providing important supporting evidence for compact merger theories for short bursts. I will focus on the highlights of the mission so far, concentrating primarily on afterglow results from the Swift X-ray Telescope.
November 2, 2005 | 3:30 PM | RI 480 | Wednesday colloquium The Structure of Early-Type Galaxies Laura Ferrarese,
The inner few hundred parsecs of galaxies are of interests for a variety of reasons. Because gas, dust and dense stellar systems are naturally drawn to the bottom of the potential well, a galaxy history is best reflected in the central regions. Dynamical processes occur faster at the center, where dynamical timescales are shorter than elsewhere in the galaxy. Finally, the centers of most galaxies host supermassive black holes, the evolution of which is intimately related to that of the surrounding galaxy. The ACS Virgo Cluster Survey (ACSVCS) targeted 100 early-type members of the Virgo cluster, from giants to dwarfs, each imaged at 7pc resolution in the g- and z-bands using the Advanced Camera for Surveys on board HST. I will discuss some very recent results from the ACSVCS, focusing in particular on the core and nuclear strucure of this fascinating
November 9, 2005 | 3:30 PM | RI 480 | Wednesday colloquium High Resolution Observations of the Cosmic Microwave Background with ACBAR. William Holzapfel, UC Berkeley
Observations of the Cosmic Microwave Background (CMB) radiation provide a window to the Universe as it existed 400,000 years after the Big Bang. This snapshot of the early Universe encodes a wealth of information about the constituents of the Universe and perhaps the mechanism of inflation. High resolution observations of the CMB are an important compliment to the results of experiments with coarser resolution such as WMAP. The Arcminute Cosmology Bolometer Array Receiver (ACBAR) is a 16 element 230mK bolometer array designed to observe the CMB with a 5' beam. ACBAR has just completed its 4th and final season of observation at the South Pole. During it's lifetime it has produced maps of the CMB with unprecedented resolution and sensitivity. I will discuss the results of the full 2-year data set (to be released soon) and extrapolate to what we can expect from the 4-year data set.
November 16, 2005 | 3:30 PM | RI 480 | Wednesday colloquium ABOUT INFLATION Lev Koffman, CITA
The top-down approach to inflation seeks to embed it in the fundamental theory. I will review recent ideas about inflation, generation of fluctuations and reheating in string theory. The bottom-up approach to inflation reconstructs from available onservables the acceleration history of the universe. I will discuss the methods of inflationary trajectories reconstruction.
November 30, 2005 | 3:30 PM | RI 480 | Wednesday colloquium Pulsars in X-rays George Pavlov, Penn State
Chandra and XMM-Newton observations of about 60 isolated (nonaccreting) pulsars have provided valuable data on the X-ray properties of these objects. Thanks to the higher sensitivity and better spectral resolution of the Chandra ACIS and XMM EPIC detectors, we can separate the thermal and nonthermal components of their spectra and study the radiation from the neutron star surfaces and magnetospheres with much higher certainty than it was possible in the pre-Chandra era. Particularly important is the high spatial resolution of Chandra data, which allows one to separate the pulsar radiation from that of compact pulsar wind nebulae (PWNe) around young pulsars and study the PWN morphology and spectra. Monitoring observations of the brightest PWNe, around the Crab and Vela pulsars, revealed stunning pictures of their complicated dynamic behavior. The large sample of pulsars and PWNe observed with the Chandra and XMM-Newton observatories made it possible to examine the correlations between various properties of these objects and their evolution. I will overview the general X-ray properties of pulsars and PWNe and present most interesting results of observations of individual objects.
December 7, 2005 | 3:30 PM | RI 480 | Wednesday colloquium UV and X-ray Observations of the Warm-Hot Intergalactic Medium Smita Mathur, Ohio State University
Hydrodynamic cosmological simulations predict that most of the baryons at low redshift reside in warm-hot intergalactic medium, WHIM. One of the few prospects for detecting this shock heated, low-density gas is via the "X-ray forest" of absorption lines it should produce in quasar spectra. Such observations are now possible with Chandra X-ray Observatory. I will describe recent efforts to trace the WHIM and determine its physical properties, with Chandra as well as with HST and FUSE, and discuss the implications towards the missing baryon problem. I will also describe the attempts to detect the Local Group baryons with X-ray and UV observations.
September 30, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Miniquasar feedback before reionization Michael Kuhlen,
I will present results from recent AMR cosmological hydro simulations modeling the radiative feedback from an early miniquasar. Accreting intermediate mass black holes are powerful sources of X-ray radiation, which is able to penetrate the cold, neutral medium before reionization and significantly alter its thermal and chemical properties. I will discuss the miniquasar's effect on the proto-IGM's temperature, clumping factor, ionization fraction, and molecular hydrogen abundance, and comment on the possibility of observing these effects via redshifted 21cm emission against the CMB.
October 7, 2005 | 12:00 PM | RI 480 | Friday noon seminar Cosmology with Galaxy Clusters Joseph Mohr,
October 14, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Just how much information about cosmology does the nonlinear galaxy power spectrum contain? Andrew Hamilton,
The technology for measuring cosmological parameters from galaxy power spectra in the linear regime is now well-developed. Yet much of the information in real galaxy surveys potentially lies at smaller, non-linear scales. Can information about cosmology be extracted from non-linear clustering? In this talk I show how to answer this question quantitatively, from measurements of the Fisher information from simulations of large scale structure. The results are surprising: at translinear scales there is an order of magnitude less information than one might have expected, whereas at just-virialized scales there is an order of magnitude more information than one might have expected. The results impel a revision of one's (mine, anyway) thinking about clustering at non-linear scales.
October 21, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Multi-Scale Growth of Cosmic Structure Juna Kollmeier,
I will discuss the growth of structure from black holes to the intergalactic medium. Turning density fluctuations into galaxies and black holes is difficult and many outstanding issues remain to be solved. I will discuss three separate ways to attack this problem on different physical scales: IGM-Galaxy correlations on small and large scales, fluorescent Lyman alpha emission from gaseous structures produced in LambdaCDM hydrodynamic simulations, and black hole mass and Eddington ratio measurements with the AGN and Galaxy Evolution Survey.
October 28, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar New constraints on the extragalactic background light from TeV astronomy Simon Swordy, Kavli Institute for Cosmological Physics
New results from TeV observations from the most distant AGN yet observed have provided some constraints on the intensity of the EBL which are becoming interesting.
November 4, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar A New look at Dark Matter in the Universe Manoj Kaplinghat,
Supersymmetric theories predict two kinds of dark matter. One kind, cold dark matter, is made up of non-relativistic weakly interacting massive particles (WIMPs). The other kind has a non-thermal distribution and they are populated by decays of WIMPs in the early universe with a natural lifetime of about a month. This model of dark matter from early decays may be distinguished from the cold dark matter model by observations of structure on scales smaller than about a megaparsec. They may not suffer from problems on the small scales that seem to beset the cold dark matter model.
November 11, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Constraints on neutrino Physics from cosmology and their impact on world neutrino data Alessandro Melchiorri,
We demonstrate that Cosmic Microwave Background anisotropies and galaxy clustering data yield an indication for primordial anisotropies in the cosmological Neutrino Background. We then derive several cosmological bounds on Neutrino Physics. The results are discussed and compared with neutrino oscillation data and upper limits on the effective neutrino mass from beta decay experiments.
November 18, 2005 | 12:00 PM | LASR Conference Room | Friday noon seminar Science results with SDSS weak lensing Rachel Mandelbaum, Princeton University
The SDSS has proven to be an excellent dataset for exploring various problems in astrophysics and cosmology using weak lensing, with the highest lensing signal to noise to date and spectroscopic redshifts for lens galaxies, which simplifies theoretical interpretation by allowing us to compute signal as a function of transverse separation rather than angle. In this talk, I will describe our new Reglens reduction method that is used to measure galaxy shapes, discuss constraints on systematic errors, and describe several interesting science results that have resulted from it. Recently, we have placed constraints on dark matter halo ellipticity, and detected intrinsic ellipticity-density alignments that may be important contaminants of current and future weak lensing surveys. I will also describe ongoing work such as a measurement of the dark matter power spectrum using a combination of galaxy-shear cross-correlation and galaxy-galaxy autocorrelation techniques; a study of the relationship between stellar masses, luminosities, and dark matter halo masses as a function of morphology and local environment; and the determination of average halo profiles using the lensing signal around field galaxies.
October 4, 2005 | 12:00 PM | LASR Conference Room | Special seminar The Sources of Intergalactic Metals Evan Scannapieco, KITP
While there are many models for intergalactic enrichment, there are very few direct constraints to distinguish between them. I will present an analysis of the size distribution and clustering of ~ 1000 Carbon-IV, Silicon-IV, Magnesium-II, and Iron-II absorbers measured in 19 high signal-to-noise QSO spectra. When combined with detailed numerical simulations of the intergalactic medium, these results place unique constraints on the objects responsible for cosmological enrichment, and the typical sizes of the regions they enriched.
November 15, 2005 | 12:00 PM | LASR Conference Room | Special seminar Testing the Isotropy of the Cosmic Microwave Background Kate Land, Imperial College
I will review some recent claims of anomalous signatures in the WMAP data of the CMB - specifically those that indicate a departure from Statistical Isotropy. This will include an outline of various methods of analysis and the issues involved in testing the Gaussianity and Statistical Isotropy of the CMB. I will then discuss the various implications of the observations - the most exciting of which is that our Universe is not Isotropic and more complicated cosmological models need to be considered.
December 6, 2005 | 12:00 PM | LASR Conference Room | Special seminar Cosmological Magnetic Field:a fossilof density perturbations in the early universe Ichiki Kiyomoto,