KICP Seminars & Colloquia, Fall 2003

Seminar schedule for Fall 2003
September 30, 2003
Special seminar
Niayesh Afshordi
Princeton University
Cross-correlating the CMB with the large-scale structure in the universe   [Abstract]
October 1, 2003
Wednesday colloquium
Alan Watson
The mass composition of cosmic rays above 10^17eV   [Abstract]
October 3, 2003
Friday noon seminar
Nick Gnedin
University of Colorado
6,10,17   [Abstract]
October 9, 2003
Thursday lunch discussion
Asantha R Cooray
The Quest for First Stars   [Abstract]
October 10, 2003
Friday noon seminar
Pengjie Zhang
Measuring the thermal history of the universe by the Sunyaev Zeldovich   [Abstract]
October 15, 2003
Wednesday colloquium
Lloyd Knox
University of California, Davis
Peculiar Velocities, Gas Temperatures and other Benefits of Multi-frequency Sunyaev-Zeldovich Observations of Galxy Clusters   [Abstract]
October 17, 2003
Friday noon seminar
Yong-Seon Song
University of California, Davis
Cosmological parameters from future CMB and cosmic shear observations   [Abstract]
October 24, 2003
Friday noon seminar
Paul Sommers
University of Utah
The Auger Observatory attacks fundamental puzzles posed by high energy cosmic rays   [Abstract]
October 29, 2003
Wednesday colloquium
Tom Weiler
Vanderbilt University
Physics to Do with Cosmic Neutrinos   [Abstract]
October 31, 2003
Friday noon seminar
Marcus Runyan
Unversity of Chicago
The ACBAR Experiment   [Abstract]
November 4, 2003
Special seminar
James Bullock
Cosmology and the Milky Way's Stellar Halo   [Abstract]
November 6, 2003
Thursday lunch discussion
Savvas M. Koushiappas
The Ohio State University
The observability of gamma-rays from neutralino annihilations in   [Abstract]
November 7, 2003
Friday noon seminar
Ariyeh Maller
University of Massachusetts
Large Scale Structure in the Two Micron All Sky Survey   [Abstract]
November 11, 2003
Special seminar
Peter Biermann
Max Planck Institute fur Radioastronomie
North versus South - the origin of the highest energy cosmic rays -   [Abstract]
November 12, 2003
Wednesday colloquium
Chris Kochanek
Ohio State
Quasar Microlensing -- Results From <10 milliMACHOS   [Abstract]
November 14, 2003
Friday noon seminar
Priyamvada Natarajan
Yale University
Probing the nature of dark matter via gravitational lensing   [Abstract]
November 21, 2003
Friday noon seminar
Emil Mottola
Dark Energy, Conformal Invariance, and the CMBR   [Abstract]
December 5, 2003
Friday noon seminar
Ishwaree Neupane
University of Taiwan
Cosmology from M-theory compactification with fluxes:Cosmic Speed-up and Dark Energy   [Abstract]
December 10, 2003
Wednesday colloquium
Mike Gladders
Carnegie Observatory
The Red-Sequence Cluster Surveys   [Abstract]
December 12, 2003
Friday noon seminar
Thomas Cox
UC (Santa Cruz)
Simulations of Collisional Starbursts   [Abstract]

  • October 1, 2003 | 3:30 PM | RI 480
    The mass composition of cosmic rays above 10^17eV
    Alan Watson, Leeds

    It is becoming clear that we will have excelent new data on the energy spectrum and mass composition of cosmic rays up to 10^20 eV within the next few years. However, it may be diffcult to make firm statements about the origin of the cosmic rays from these data alone and we also need new information on the mass composition above 10^17 eV. I will review the present situation, showing that, while there is currently much confusion, there is also some hope for the future.
  • October 15, 2003 | 3:30 PM | RI 480
    Peculiar Velocities, Gas Temperatures and other Benefits of Multi-frequency Sunyaev-Zeldovich Observations of Galxy Clusters
    Lloyd Knox, University of California, Davis

    We will soon have SZ surveys conducted from four continents and from space as well. I will review the motivation for these surveys and then concentrate on the benefits of flux measurements at multiple frequencies. Such measurements of galaxy clusters in the 30 to 350 GHz range can be used to simultaneously determine a galaxy cluster's integrated pressure along the line of sight, its bulk velocity with respect to the cosmic microwave background (CMB), and its mass-weighted average gas temperature. I will show how the Sunyaev-Zeldovich effects make these determinations possible in principle and how contamination from the CMB itself, from high-redshift dusty galaxies and from synchrotron-emitting cluster galaxies can be controlled, making it possible in practice. I will highlight the benefits of multi--frequency measurements to a broad range of cosmological applications.
  • October 29, 2003 | 3:30 PM | RI 480
    Physics to Do with Cosmic Neutrinos
    Tom Weiler, Vanderbilt University

    We begin with a brief overview of extreme-energy (EE) cosmic ray data, arguments for EE cosmic neutrinos, and the experiments which will perform neutrino astronomy. Next we discuss particle physics aspects of neutrinos which can best(or only) be probed using the large energy E or large distance L or cosmic sources. Potentially measurable neutrino physics includes the detection of the relic neutrino density liberated one second after the big-bang, finite neutrino lifetimes, and neutrino doubling ("pseudo-Dirac" neutrinos). The neutrino-nucleon cross-section at a CMS energy orders of magnitude beyond terrestrial accelerators is also accessible.Measurement of an anomalously large neutrino cross-section would indicate radically new physics(e.g. low string-scale, extra dimensions, precocious unification),while a smaller than expected cross-section would reveal an aspect of QCD evolution.
  • November 12, 2003 | 3:30 PM | RI 480
    Quasar Microlensing -- Results From <10 milliMACHOS
    Chris Kochanek, Ohio State

    Quasar microlensing is the forgotten stepchild of microlensing experiments primarily because it seemed too difficult to convert the observational data into physical results. We have developed an analysis method that can be applied to quasar microlensing data of arbitrary complexity and apply it to the OGLE data for the four-image quasar lens Q2237+0305. The results are surprisingly good given that the data set is equivalent to 2 weeks of observations by a large Galactic microlensing project. We estimate the stellar mass fraction, the average stellar mass, the size of the quasar accretion disk and the mass of the quasar black hole.
  • December 10, 2003 | 3:30 PM | RI 480
    The Red-Sequence Cluster Surveys
    Mike Gladders, Carnegie Observatory

    The Red-Sequence Cluster Survey is an ~100 square degree imaging survey in the R and z' filters designed to locate and characterise galaxy clusters to redshifts as high as 1.4. After a brief discussion of the survey motivation, execution and basic results, this talk will focus on recent science results arising from the RCS cluster catalogs. Topics will include strong lensing by clusters and the properties of a sub-sample of RCS clusters at z>1. Time permitting, I will also discuss recent work aimed at quantifying the evolution of the radio source population in clusters over the entire RCS redshift range, and the global correlations between large scale structure as traced by both AGN and clusters.


  • October 3, 2003 | 12:00 PM | LASR Conference Room
    Nick Gnedin, University of Colorado

    Cosmological reionization-the process of ionization of the bulk of cosmic gas by ultra violet radiation from primeval galaxies-is by far the most dramatic event that occurred in the universe since the formation of the first star. I will overview recent observational and theoretical progress(and regress)in our understanding of reionization, and will discuss the future observational avenues that are going to open for us in the next decade.
  • October 10, 2003 | 12:00 PM | LASR Conference Room
    Measuring the thermal history of the universe by the Sunyaev Zeldovich
    Pengjie Zhang, FNAL

    The Sunyaev Zeldovich (SZ) effect directly probes the thermal and kinetic energy of ionized baryons and so is a sensitive measure of the thermal history of the universe. I will discuss the two key ingredients of its precision modeling: analytical models and hydrodynamic simulations. I will address various limitations in these two approaches and the way to quantify and overcome them. I will then forecast the power of planned SZ experiments to measure the thermal history of the universe.
  • October 17, 2003 | 12:00 PM | LASR Conference Room
    Cosmological parameters from future CMB and cosmic shear observations
    Yong-Seon Song, University of California, Davis

    Precision cosmological observations can determine a large number of cosmological parameters which are the keys to understanding the Universe. I sort out all parameters into three types:primordial parameters(primordial power spectrum amplitudes, scalar tilt, tensor tilt, etc.),intermediate parameters (which are mainly determined at last scattering surface) and low-redshift parameters(neutrino mass, dark energy,etc.). Future CMB experiments will allow us to determine the primordial parameters and intermediate parameters. With the primordial and intermediate parameters highly constrained, low-redshift observations can be used to place amazingly tight constraints on the low-redshift parameters. In particular I show how the dark energy component's equation-of-state parameter can be determined as a function of redshift with future observations such as LSST nd Planck or CMBpol.
  • October 24, 2003 | 12:00 PM | LASR Conference Room
    The Auger Observatory attacks fundamental puzzles posed by high energy cosmic rays
    Paul Sommers, University of Utah

    Observations of cosmic rays above the expected GZK spectral cut off have challenged every model of their production and propagation. The Auger Observatory will provide copious high-quality data to disspell the mysteries and identify the sources of high energy cosmic rays. Its collecting power will exceed that of previous experiments by more than an order of magnitude. It will have full-sky coverage for sensitive anisotropy analyses. Exploiting the combination of surface detectors and air fluorescence detectors, it will accurately measure the energy and arrival detection of each cosmic ray, and it can statistically determine the types of primary particles. The observatory in Argentina is now operational and growing day by day.
  • October 31, 2003 | 12:00 PM | LASR Conference Room
    The ACBAR Experiment
    Marcus Runyan, Unversity of Chicago

    I will discuss the Arcminute Cosmology Bolometer Array (ACBAR) experiment which made observations of small-scale CMB anisotropy from the South Pole in 2001 and 2002. ACBAR is a multi-frequency millimeter-wave bolometer array with ~5' resolution from the 2m Viper telescope. I will describe the instrument and the results from the first two years of the project, as well as expectations from observations in 2004 and 2005.
  • November 7, 2003 | 12:00 PM | LASR Conference Room
    Large Scale Structure in the Two Micron All Sky Survey
    Ariyeh Maller, University of Massachusetts

    The recently completed Two Micron All Sky Survey (2MASS) is the largest catalog of near infrared data, containing more than 500 million stars and 1.6 million extended sources. The near infrared offers us the opportunity to study galaxies in a band where dust obscuration is minimized and for which mass-to-light ratios vary the least. I will discuss large scale structure in 2MASS, focusing on the angular correlation function and the flux dipole we measure using 2MASS galaxies. The flux dipole is 16 degrees from the CMB velocity dipole, where this offset seems to be entirely due to the contribution of the few hundred brightest galaxies. >From comparing the acceleration of the Local Group from the flux dipole with our motion with respect to the CMB I find that K-band selected galaxies are unbiased tracers of the mass distribution. I will show that the angular correlation function of 2MASS galaxies deviates significantly from a pure power law as expected in halo occupation models. Finally I will invert the angular correlation function to determine the power spectrum of K-band selected galaxies which is well fit by a CDM type power spectrum on linear scales.
  • November 14, 2003 | 12:00 PM | LASR Conference Room
    Probing the nature of dark matter via gravitational lensing
    Priyamvada Natarajan, Yale University

    Galaxy-galaxy lensing in clusters provides constraints on properties of early-type galaxy halos. The tidally truncated radii thus inferred from these studies is then used to obtain constraints on the nature of dark matter. Current observations of HST cluster-lenses strongly rule out fluid-like equations of state and are in fact consistent with collisionless dark matter.
  • November 21, 2003 | 12:00 PM | LASR Conference Room
    Dark Energy, Conformal Invariance, and the CMBR
    Emil Mottola, LANL

    The discovery of dark energy comprising some 70% of the energy density of the universe has brought the long-standing cosmological constant problem to the attention of observational cosmologists. The consistent treatment of quantum vacuum energy in gravity and cosmology very likely requires some revision in classical general relativity. The minimal revision required is the inclusion of the trace anomaly of massless fields, whose fluctuations do not decouple from the metric even at the very largest space and time scales. The trace anomaly predicts a conformally invariant phase of gravity, which has consequences for the spectrum and statistics of the CMBR. Conformal invariance leads in general to deviations from naive classical scaling. The spectral index of the two-point function of density fluctuations is given in terms of the quantum trace anomaly and is greater than one, leading to less power at large distance scales than a strict Harrison-Zel'dovich spectrum. Conformal invariance also implies non-gaussian statistics for the higher point correlations and completely determines the large angular dependence of the three-point correlations of the CMBR.
  • December 5, 2003 | 12:00 PM | LASR Conference Room
    Cosmology from M-theory compactification with fluxes:Cosmic Speed-up and Dark Energy
    Ishwaree Neupane, University of Taiwan

    I discuss the time-dependent compactifications of higher-dimensional gravity models and M-theory with fluxes to generate a potential for the moduli. I analyse some exact complicated scalar potentials for the dimensionally reduced effective theories, present various solutions that lead to a transient period of acceleration of the 4D spacetime(universe),and examine on the possibility of obtaining sufficient inflation by warped and product space complifications, in general. I will also comment upon the cosmic acceleration due to negative powers of curvatures in modified gravity in four and higher dimensions, including some gravitational tests.
  • December 12, 2003 | 12:00 PM | LASR Conference Room
    Simulations of Collisional Starbursts
    Thomas Cox, UC (Santa Cruz)

    There is mounting evidence that galaxy interactions play an important role in galaxy evolution. Elliptical galaxies, spiral bulges, and a significant fraction of all the stars in the universe may be byproducts of galaxy mergers, especially mergers at high redshift. In order to better understand the roles mergers play in galaxy evolution we are using high resolution N-body simulations, including hydrodynamics and star formation, to sample the large parameter space of pre-merger galaxy properties and interaction parameters. We briefly discuss how this improves upon previous work in this area and demonstrate how our simulations can be used as inputs to semi-analytic models of galaxy formation. Finally, we show how mock observations of our simulations can provide insight into observations of galaxy spectra and morphologies.


  • September 30, 2003 | 3:00 PM | LASR Conference Room
    Cross-correlating the CMB with the large-scale structure in the universe
    Niayesh Afshordi, Princeton University

    The fluctuations of the CMB at angles larger than a degree are mostly of primordial nature. Cross-correlating these fluctuations with the observable tracers of matter(e.g. galaxies, clusters, and cosmic shear gives us a unique way of extracting small secondary anisotropies that probe the low redshift universe. In this talk, I will discuss the dominant sources of the cross-correlation signal, i.e. ISW and the thermal SZ. The ISW effect is seen on large angles and is a direct probe of the dark energy, while the thermal SZ effect dominates smaller angles and probes the hot gas inside galaxy clusters. I will describe the current observational status, as wll as theoretical expectations for detection of each signal.
  • November 4, 2003 | 12:00 PM | LASR Conference Room
    Cosmology and the Milky Way's Stellar Halo
    James Bullock, Harvard/CfA

    If the LCDM cosmology is correct, then the Milky Way's dark matter halo should have accreted many tens of dwarf galaxies in the last ten billion years. Roughly have of these systems should have been tidally disrupted, and the stellar halo of our Galaxy should be made in large part by the debris of these disruption events. Evidence for this process should be visible as substructure in the outer stellar halo. I discuss efforts to model the accretion and disruption history of the Milky Way using idealized N-body simulations and discuss how deep probes of the stellar halo could test whether structure formation is truly hierarchical on small scales.
  • November 11, 2003 | 1:30 PM | LASR Conference Room
    North versus South - the origin of the highest energy cosmic rays -
    Peter Biermann, Max Planck Institute fur Radioastronomie

    Using the jet-disk symbiosis theory, which describes electromagnetic emissions of jets from stellar to supermassive black hole systems we estimate the possible cosmic ray contributions from nearby black hole systems in the local universe. We determine both cosmic ray flux, and maximum particle energy, both as upper limits. Allowing for the possibility that other particles are formed in local interactions in the host galaxy yields possible sources at cosmological redshifts. In order for just a few sources to account for the observations, rather thorough magnetic mixing of orbits is required, and so we also discuss possible models for the local magnetic field topology. However, the cosmological local black hole systems yield some very clear candidates: M87 in the North and Cen A in the South can easily account for almost all cosmic ray flux above $3 imes 10^{18}$ eV. So, we have the choice of two alternatives: Either we have a) many sources at cosmological redshifts, and require a new particle to be created at nearly the full flux possible for protons (possibly enhanced by relativistic boosting), and looking like a proton or neutron in airshowers, or b) we have rather thorough magnetic orbital mixing without enhancing the path length in the latter case M87 produces a moderate flux, but to very high energy of particles, in the North, and Cen A produces a large flux, only to a few $10^{19}$ eV, in the South.


  • October 9, 2003 | 12:00 PM | LASR Conference Room
    The Quest for First Stars
    Asantha R Cooray, Caltech

    Recent cosmic microwave background anisotropy results from the Wilkinson Microwave Anisotropy. Probe suggest that the universe was reionized at a redshift around 20. Such an early reionization could arise through the ionizing radiation emitted by first stars at redshifts of 15 and higher. We discuss a possibility to detect the prescence of such stars through measurements of the near infrared background surface brightness spatial fluctuations. We show that the contribution to the angular scales and thi excess can be potentially detected when resolved foreground galaxies out to a redshift of a few are removed from the clustering analysis. We are planning a rocket-based experiment for this purpose and we will discuss th extent to which first stars can be identified with the Near Infrared Fluctuation Experiment (NIFE) and ASTRO-F.
  • November 6, 2003 | 12:00 PM | LASR Conference Room
    The observability of gamma-rays from neutralino annihilations in
    Savvas M. Koushiappas, The Ohio State University

    I estimate the probability of detecting gamma-rays from the annihilation of neutralino dark matter in dense, central regions of Milky Way substructure. I model Galactic substructure statistically based on Monte Carlo realizations of the formation of a Milky Way-like halo using semi-analytics method that have been calibrated against the results of cosmological N-body simulations. I find that it may be possible for the upcoming experiments GLAST and VERITAS, working in concert, to detect gamma-rays from dark matter substructure if the neutralino is relatively light ($Mchi lsim 100 GeV$), while for $Mchi gsim 500 GeV$ such a detection seems unlikely. I perform most of my calculations within the framework of the standard $Lambda$CDM cosmological model however, I also investigate the robustness of these results to various assumptions and find that the probability of detection is sensitive to poorly-constrained input parameters, particularly those that characterize the primordial power spectrum such as spectral running and/or neutrino mass. Specifically, the best-fitting power spectrum of the WMAP team, with a running spectral index, predicts roughly a factor of fifty fewer detectable subhalos compared to the standard $LCDM$ cosmological model with scale-invariant power spectrum. I therefore conclude that the lack of a detected gamma-ray signal gives very little information about the supersymmetric parameter space due to uncertainties associated with both the properties of substructure and cosmological parameters. I also conclude that extrapolating the mass function of substructure to masses much smaller than those resolved in simulations may not necessarily lead to an abundance of detectable substructure.