April 7, 2004 | 3:30 PM | RI 480 | Wednesday colloquium Gamma-Rays, Cosmic Backgrounds and the Universe, as Calorimeter Scott Wakely, University of Chicago
Over long distances, the Universe is largely opaque to very high energy (VHE) radiation. I'll talk about the implications of this for GeV/TeV gamma-ray measurements, and discuss some possible methods for inferring interesting cosmological information about the production and composition of extragalactic background radiation fields at different wavelengths.
April 14, 2004 | 3:30 PM | RI 480 | Wednesday colloquium Two Tests of Environmental Affects on Galaxy Formation Ravi Sheth, University of Pittsburgh
Galaxy formation models make specific predictions for how the properties of galaxies depend on enviroment. I will outline the physical assumptions on which these predictions are based, and will then describe some tests of these assumptions which can be made with galaxy surveys which are just becoming available.
May 5, 2004 | 3:30 PM | RI 480 | Wednesday colloquium 21 cm fluctuations: a new window for cosmology Matias Zaldariagga,
I will discuss what 21 cm fluctuations produced by gas at high redshift can teach us about cosmology. I will discuss some of the challenges in making these observations.
May 19, 2004 | 3:30 PM | RI 480 | Wednesday colloquium Eternal Inflation, Multiple Universes, and other Dark Matters Anthony Aguirre, Institute for Advanced Study School of Natural Science
Several ideas in cosmology, including inflation, string cosmology, and quantum cosmology, have led to the notion of multiple "universes" with different properties. This immediately raises the question of which (theoretical) universe we should compare to ours, and also provides a context for application of the "anthropic principle". I will outline some of the issues and problems that arise in multiverse theories, and describe some specific progress that has been made toward resolving (or making more acute) these problems.
April 2, 2004 | 12:00 PM | LASR Conference Room | Friday noon seminar Adventures with Cold Dark Matter Halo Substructure Andrew Zentner, Center for Cosmological Physics
I will try to use this talk to address several issues. I plan to begin with a brief introduction to an approximate, analytic calculation of the properties of cold dark matter halo substructure by discussing a problem that many of you are likely rather familiar with, the problem of "missing" dwarf satellites of the Milky Way. I will discuss how such analytic models can be used to probe a wide range of parameter space and how such simple calculations can point towards ways in which substructure can be used as a cosmological probe. After this introduction to the model and some of it's virtues and drawbacks, I will discuss a project to use this model to better understand the physics of galaxy clustering. In particular, I will use this model in conjunction with the Halo Model to show how the processes of satellite accretion, mass loss due to tidal forces and dynamical friction all play a role in determining the galaxy correlation function. In the spirit of having the seminars be an informal discussion meeting, I have chosen to present work that is very much still in progress. As such, I have a request from the audience: Please ask questions! Because this work is in a developmental phase, it can still benefit greatly from questions and criticisms (however harsh) and if I can't finish, that will leave material that I can discuss on another Friday.
April 16, 2004 | 12:00 PM | LASR Conference Room | Friday noon seminar Revisiting Hawking Radiation in Odd Spacetime Dimensions Daniel Chung, University of Wisconsin
April 23, 2004 | 12:00 PM | LASR Conference Room | Friday noon seminar On Beyond Lambda: Dark Energy in the Next Generation Eric Linder, LBL
The acceleration of the expansion of the universe points toward new physics frontiers in cosmology, high energy physics, and gravitation. I examine various cosmological probes of the nature of dark energy, emphasizing the challenges in systematics control of the observations and interpretation of the data. Next generation experiments such as the Supernova/Acceleration Probe (SNAP) provide powerful, complementary tests I discuss what Joint Dark Energy Measurements can (and can't) tell us about going on beyond Lambda.
April 30, 2004 | 12:00 PM | RI 480 | Friday noon seminar Galaxy environments and galaxy formation at low redshift David Hogg, New York University
(1) Galaxy environments are much more closely related to galaxy spectral properties (ie, star formation histories) than they are related to galaxy structural properties (ie, morphological properties). (2) We can see new galaxy bulges being created in the local Universe,and they are being created at a rate that corresponds to about one percent of the galaxy population per Gyr.
May 7, 2004 | 12:00 PM | LASR Conference Room | Friday noon seminar Massive galaxies at high redshift in GOODS: observations in the context of LCDM, and challenges for galaxy & star formation theory Lexi Moustakas, Space Telescope Science Institute
May 14, 2004 | 12:00 PM | LASR Conference Room | Friday noon seminar String cosmology and other inflated opinions Emil Martinec, University of Chicago
String theory provides a context for inflationary cosmology in the framework of a comprehensive theory of gravity and particle physics. The basics of string theory and a few of the current scenarios for inflation within it will be described. Some of the obstacles to further progress will also be discussed.
May 21, 2004 | 12:00 PM | LASR Conference Room | Friday noon seminar MAGIC: a Framework for Cosmological Data Analysis Ben Wandelt, University of Illinois Urbana-Champaign
I will discuss powerful statistical techniques which are intended to enable the optimal analysis of real cosmic microwave background data. These techniques allow the exact propagation of statistical uncertainty about the power spectrum from the map (or time-ordered data) to the cosmological parameters under very general assumptions. New features of these methods include the ability to account for correlated noise, arbitrarily shaped observed regions on the sky, specify partial knowledge about foreground contributions in a very flexible way and to incorporate physical priors, if desired. I will present a preliminary application of these methods to the issue of the low power at low l in WMAP and COBE. If time permits, I may mention the promise these methods hold for optimal analyses of other astronomical data sets.
May 28, 2004 | 12:00 PM | LASR Conference Room | Friday noon seminar Astrophysics of Dark Energy Stars George Chapline, Lawrence Livermore National Laboratoy
Certain predictions of general relativity such as event horizons and closed time-like curves cannot be physically correct for the simple reason that they are inconsistent with ordinary quantum mechanics. On the other hand the overwhelming experimental evidence for relativistic kinematics suggests that general relativity ought to be correct. These seemingly conflicting points of view can be reconciled if it is assumed that an infinite red shift surface corresponds to a quantum critical point of the vacuum of space-time. This leads to an entirely new picture of objects that lie within their Schwarzschild radius, and a new perspective on a variety of astrophysical phenomena including supernovae explosions, gamma ray bursts, relativistic jets, dark energy, and dark matter.
June 4, 2004 | 12:00 PM | LASR Conference Room | Friday noon seminar From Spitzer to Herschel and Beyond: The Future of Far-Infrared Space Astrophysics Joel Primack, UC,Santa Cruz
I will present 1) recent results of semi-analytic galaxy formation models and compare them to the latest from SDSS, GOODS, GEMS, and other searches for high-redshift galaxies 2) new results from the galaxy merger simulations, now including stellar SED modelling and radiative transfer through dust. 3) New techniques for the non-parametric morphological classification of galaxies
June 18, 2004 | 12:00 PM | LASR Conference Room | Friday noon seminar Precession, Polaris and the Age of the Pyramids or Ancient Egyptian Astrometry Matthew Hedman, Kavli Institute for Cosmological Physics
Just last Quarter, I gave the 59th Compton Lecture Series entitled "The Age of Things: Sticks, Stones, and the Universe." This mutli-disciplinary series of talks dealt with various methods of determining when events happened in the past. Topics covered in these talks included: the recent reconstruction of Ancient Mayan History from dated historical texts the current efforts to determine the timescale of mammalian evolution using molecular dating, and the new estimates of the age of the universe from cosmological data. The second lecture in this series, entitled "Precession, Polaris and the Age of the Pyramids" provides a good example of the cross-disciplinary thrust of these lectures. While the Great Pyramids are among the most impressive ancient monuments on earth, historical records do not yet provide a precise date for the construction of these impressive monuments (residual uncertainties are as large as hundreds of years). Recently, a new method of estimating the age of the pyramids has been proposed, which combines astronomical and archaeological data in a very productive way. If this proposed method works, then the age of the pyramids can be measured to within a decade or so, which would place important new constraints on the chronology of the earliest history of Ancient Egypt.
June 17, 2004 | 2:00 PM | LASR Conference Room | Special seminar A Search for TeV Emission from X-ray Selected AGN Using the Milagro Observatory Liz Hays, University of Maryland
A TeV emission component has been detected for several active galactic nuclei (AGN). The majority of TeV detections of AGN are for nearby (z<0.13) X-ray selected BL Lacs in flaring states. The variability of these sources makes continuous monitoring necessary to detect flaring activity. The Milagro gamma-ray observatory is a wide-field (~2 sr) instrument that operates continuously allowing daily observations of the Northern hemisphere. A real time search of the overhead sky for transient activity on timescales of 2 hours and longer has been conducted for the last 2 years. No detections of unidentified sources have been made in this search to date. The Crab Nebula and Mrk 421 are the highest significance locations in the full map. The most significant locations not associated with known TeV sources are of interest for continued monitoring and comparison with results from other instruments. A similar transient analysis is used to set limits on the time-integrated behavior of a selected sample of BL Lacs. Costamante and Ghisellini (2002) present a selection of BL Lacs with X-ray and radio flux levels favorable for TeV emission and make predictions for the TeV flux levels. Twenty-seven objects selected from this sample are the subjects of a search for TeV emission on time scales from 8 days to 2.8 years in data taken between December 15, 2000, and September 8, 2003. None of the selected BL Lacs are detected on any of the time scales. Flux limits are available for each object and time scale and comparisons are made with the predicted emission.
May 6, 2004 | 12:00 PM | LASR Conference Room | Thursday lunch discussion Thermonuclear Supernovae: Predictions versus Observations Wolfgang Hillebrandt, Max Planck Institute for Astrophysics
Recent progress in modelling type Ia supernovae by means of 3-dimensional hydrodynamic simulations is addressed. Our models are based on the assumption that thermonuclear burning inside a Chandrasekhar-mass C+O white dwarf is similar to turbulent chemical combustion and that, thus, thermonuclear supernovae can be modelled by means of numerical methods which have been developed and tested for laboratory and technical flames. It is shown that these models have considerable predictive power and allow to study observable properties of type Ia supernovae, such as their light curves and spectra, without adjustable non-physical parameters. This raises a quest for better data, covering the spectroscopical and photometric evolution in all wave bands from very early epochs all the way into the nebular phase. First such results obtained by the European Supernova Collaboration (ESC) for a sample of nearby SNe Ia and their implications for constraining the models and systematic differences between them are also discussed.