March 30, 2011 | 3:30 PM | RI 480 | Astronomy Colloquium A generative model of everything in the Universe (including astrophysicists) David Hogg, New York University
April 6, 2011 | 3:30 PM | RI 480 | Astronomy Colloquium Radio astronomical studies of galaxy formation: the dense gas history of the Universe and the ALMA/EVLA revolution Chris Carilli, NRAO
Deep optical and near-IR surveys have traced the star formation history of the Universe as a function of environment, stellar mass,and star formation rate, back to cosmic reionization and the first galaxies (z > 6). While progress has been truly impressive, near-IR studies of early galaxies are fundamentally limited in two ways: (i) obscuration of rest-frame UV emission by dust, and (ii) near-IR studies reveal only the stars and ionized gas, thereby missing the evolution of the cool gas in galaxies, the fuel for star formation. Line and continuum studies at radio wavelengths (cm through submm) address both these issues, by probing deep into the earliest, most active, and dust obscured, phases of galaxy formation, and by revealing the molecular and cool atomic gas. I will summarize the techniques of radio astronomy to perform these studies, then present two recent examples. The first will consider the atomic and molecular gas, dust, and star formation, in the host galaxies of z ~ 6 quasars. The host galaxies are under-going extreme starbursts, with star formation rates > 1000 Mo/year, and molecular gas masses in excess of 1e10 Mo. Through gas dynamics, we can estimate the ratio of the bulge mass to black hole mass. These observations imply that we are witnessing the co-eval formation of massive elliptical galaxies, and super-massive black holes, within 1 Gyr of the Big Bang. The second entails observations of normal galaxy formation during the 'epoch of galaxy assembly' (z ~ 1.5 to 2.5). These observations reveal massive gas reservoirs without hyper-starbursts, and that active star formation occurs over a wide range in galaxy stellar mass. We find that the peak epoch of star formation in the Universe also corresponds to an epoch when the baryon content of galaxies was dominated by molecular gas, not stars. I will conclude with a description and status report of the Atacama Large Millimeter Array, and the Expanded Very Large Array. These telescopes represent an order of magnitude, or more, improvement over existing observational capabilities from 1 GHz to 1 THz, promising to revolutionize our understanding of galaxy formation.
April 13, 2011 | 3:30 PM | RI 480 | Astronomy Colloquium Bringing our Galaxy's Supermassive Black Hole and its Environs into Focus with Laser Guide Star Adaptive Optics Andrea Ghez, UCLA
The proximity of our Galaxy's center presents a unique opportunity to study a galactic nucleus with orders of magnitude higher spatial resolution than can be brought to bear on any other galaxy. After more than a decade of astrometry from diffraction-limited speckle imaging on large ground-based telescopes, the case for a supermassive black hole at the Galactic center has gone from a possibility to a certainty, thanks to measurements of individual stellar orbits. The advent of adaptive optics technology has significantly expanded the scientific reach of our high-spatial-resolution infrared studies of the Galactic center. In this talk, I will present the results of several new adaptive optics studies on (1) our current understanding of the galaxy's central gravitational potential, (2) the puzzling problem of how young stars form in the immediate vicinity of the central black hole, (3) the surprising, apparent absence of the predicted central stellar cusp around the central supermassive black hole (an essential input into models for the growth of nuclear black holes), and (4) how future large ground-based telescope may allow these studies to test general relativity and cosmological models.
April 20, 2011 | 3:30 PM | RI 480 | Wednesday colloquium Gamma-ray Burst Afterglows as Cosmic Probes Hsiao-Wen Chen, University of Chicago
Gamma-ray bursts are among the most energetic events in the universe. Many bursts are followed by extremely luminous optical afterglows that can serve as a sensitive probe of "dark", intervening baryonic matter in space. I will review recent progress in our understanding of interstellar medium and intergalactic matter in the distant universe based on observations of long-duration gamma-ray bursts.
April 27, 2011 | 3:30 PM | RI 480 | Wednesday colloquium The Effects of Small Scale Inhomogeneities on Large Scale Dynamics in Cosmology Robert Wald, University of Chicago
Nonlinear gravitational phenomena associated with small scale (as compared with the Hubble radius) density inhomogeneities are prevalent throughout our universe. Could the nonlinear effects of these small scale inhomogeneities produce significant effects on the large scale dynamics that are not properly taken into account by standard FLRW models, which treat the matter distribution as homogeneous? I will describe recent work with S. Green that provides a framework within the context of general relativity that allows one to analyze this issue in a mathematically precise manner. Within this framework we prove quite generally that, provided that matter satisfies the weak energy condition (i.e. has positive energy density in all frames), the “effective gravitational stress energy” associated with small scale inhomogeneities also must satisfy the weak energy condition and must be traceless---corresponding to gravitational radiation. In particular, nonlinear effects of small scale inhomogeneities cannot be responsible for the acceleration of our universe. We also analyze cosmological perturbation theory within this framework and calculate the corrections produced by small scale inhomogeneities to the equations satisfied by long wavelength perturbations.
May 4, 2011 | 3:30 PM | RI 480 | Wednesday colloquium Unveiling the Cosmic Far-IR Background with Herschel: The Nature of Dusty Star-Forming Galaxies Asantha Cooray, University of California Irvine
The talk will summarize latest results from HerMES and H-ATLAS extragalactic surveys at 250, 350 and 500 microns with the SPIRE instrument on the Herschel Space Observatory. HerMES is the multi-tiered SPIRE instrument GTO survey covering about 70 square degrees on a variety of extragalactic fields with existing ancillary data. H-ATLAS is currently the largest open-time program in Herschel with 600 hours of observations to map 550 square degrees. I will discuss a newly discovered population of lensed sub-mm galaxies, the halo properties of bright and faint sub-mm galaxies as revealed by clustering and fluctuation studies, evolution of dust and molecular properties, the role of sub-mm sources in galaxy formation and evolution models, sub-mm source follow-up effort, and the future of sub-mm astronomy. I will also summarize the scientific goals of the Herschel-SPIRE Legacy Survey, a program now under discussions with ESA to cover 1500 sq. degrees with SPIRE in a fast-scan mode with the ultimate goal of recovering a catalog of 1.5 million bright sub-mm sources for future studies with ALMA, CCAT, and SPICA.
May 11, 2011 | 3:30 PM | KPTC 106 | Astronomy Colloquium The Circumgalactic Medium: 50 Years of Intellectual History and the Latest News from HST/COS Jason Tumlinson, Space Telescope Science Institute
In recent years we have come to appreciate the great importance of the gas just outside galaxies - the circumgalactic medium - to galaxy formation and evolution. I will survey the intellectual history of this subject going back to the 1960s before presenting the latest results from two large HST projects that are using the new Cosmic Origins Spectrograph to systemically characterize the gaseous halos of low-redshift galaxies. COS has uncovered a clear link between star formation and hot gas in gaseous halos beyond 100 kpc, and strong indications of winds propagating from star-forming galaxies. These results show that the circumgalactic medium likely does participate in the ongoing star formation and evolution of modern galaxies.
May 18, 2011 | 3:30 PM | KPTC 106 (talk) | Wednesday colloquium Inflation, infinity, equilibrium and the observable Universe Andy Albrecht, University of California, Davis
Cosmic inflation has given us a remarkably successful cosmological phenomenology. But the original goal of explaining why the cosmos is *likely* to take the form we observe has proven very difficult to realize. I first review the popular idea of "eternal inflation" with an eye on the roles various infinities have (both helpful and unhelpful) in our current understanding. I then discuss attempts to construct an alternative cosmological framework that is truly finite using ideas about equilibrium and dark energy. I report some recent results that point to observable signatures.
May 25, 2011 | 3:30 PM | KPTC 106 | Wednesday colloquium The Multiple Crossroads of Clusters of Galaxies August Evrard, University of MIchigan
In this talk, I will present galaxy clusters as systems spanning multiple spaces: the traditional crossroads of astrophysics and cosmology as well as the fast developing crossroads of theory, computation and observation. While the current paradigm for large-scale structure formation - a hierarchical web of quasi-equilibrium halos emerging from a noise field imposed by inflation - is largely secure, important details ranging from the profound (nature of dark energy) to the practical (rate of star formation as a function of galactic environment) remain poorly understood. Clusters of galaxies present opportunities for detailed testing of cosmological and astrophysical models, and I will discuss challenges posed by survey selection and cluster characterization. What's clear is that precise analysis of the cluster population requires that theory/computation meet observation on a common ground. The angle-wavelength space of the sky offers a natural crossroads for such a meeting, and this choice imposes new requirements on the community to build an efficient "cosmic sky machine". I will sketch ideas for developing community-wide cyberinfrastructure that could accelerate the pace of understanding cosmic structure formation.
June 1, 2011 | 3:30 PM | KPTC 106 | Astronomy Colloquium The diverse, yet orderly lives of galaxies Mariska Kriek, Center for Astrophysics, Harvard
At first glance the galaxy population today and even more so at earlier times exhibits a huge diversity. However, the well-known correlations between different galaxy properties, such as spatial structure, stellar population, stellar mass, stellar dynamics, and environment suggest that galaxy formation is actually an orderly process. With the recent large photometric and spectroscopic surveys and new instrumentation on the Hubble Space Telescope, it is now finally possible to study galaxies in a systematic way at earlier times, so that we can see directly how these relations change over cosmic time and what the physical processes are that drive them. Until very recently, these studies were hampered by the small sizes of spectroscopic galaxy samples, whereas much larger photometric samples lack the required spectroscopic information. I will discuss a novel approach, that makes use of medium-band photometry to perform detailed spectroscopic studies of ~3500 galaxies at 0.5
April 8, 2011 | 12:00 PM | LASR Conference Room | Friday noon seminar Propagation of Galactic Cosmic Rays: The Measurement of the Boron-to-Carbon Ratio of TRACER Andreas Obermeier, Radboud Universiteit Nijmegen
The big question in cosmic-ray physics is still open: What are the cosmic-ray sources and their properties? In order to be able to investigate the sources, the propagation of cosmic rays through the Galaxy must be understood, since it modifies the source spectra until they can be observed at the Earth. In a simple propagation model a cosmic-ray particle may reach the Earth, may escape the Galaxy, or may spallate into a lighter, secondary nucleus. The faster the escape from the Galaxy takes place, the fewer secondary nuclei are produced. Therefore, information on the propagation of Galactic cosmic rays can be inferred from the abundance ratio of secondary to primary cosmic-ray elements, like the boron-to-carbon ratio. Measuring this ratio poses formidable experimental challenges as the observations have to be conducted above the atmosphere and large exposure is needed to reach high energies. The TRACER detector was designed to achieve this measurement. It is currently the largest balloon-borne detector and capable of detecting cosmic rays well into the TeV/amu energy region with single element resolution. Here we present the results of the last long-duration balloon flight of TRACER, including a new measurement of the boron-to-carbon ratio up to 2 TeV/amu. We also present implications of this measurement for cosmic-ray propagation and, subsequently, their sources.
April 15, 2011 | 12:00 PM | LASR Conference Room | Friday noon seminar Elements of MHz Radio Emission and Radio Detection of the Electric Field Emitted by the Extensive Air Showers Benoit Revenu, SUBATECH, CNRS
The properties of ultra-high energy cosmic rays have to be inferred from the extensive air shower (EAS) of secondary particles that they produce in the atmosphere. Our current EAS detection technique involves two components. The first employs instruments deployed in a large surface array that sample the particle density as the EAS arrives. Then, the second uses telescopes to collect the fluorescence light emitted from atmospheric nitrogen excited by charged particles of the EAS. An alternative detection approach could be the radio detection of the electric field emitted by the charged particles of the EAS. I will present some basics of radio emission in the MHz range and show that the predicted signal is representative of the longitudinal profile of the EAS allowing the identification of the incoming cosmic ray. Then, we will discuss the experimental aspect of this domain with the presentation of the CODALEMA experiment installed at the Nancay Observatory in France. Finally, the last results from the radio detection experiments located at the site of the Pierre Auger Observatory will be presented.
April 22, 2011 | 12:00 PM | LASR Conference Room | Friday noon seminar Primordial Non-Gaussianity in Large-scale Structure Marilena LoVerde, Institute for Advanced Study
Primordial non-Gaussianity is among the most promising of few observational tests of physics at the inflationary epoch. At present non-Gaussianity is best constrained by the cosmic microwave background, but in the near term large-scale structure data may be competitive so long as the effects of primordial non-Gaussianity can be modeled through the non-linear process of structure formation. I will discuss recent work modeling effects of a few types of primordial non-Gaussianity on the large-scale halo clustering and the halo mass function. More specifically, I will compare analytic and N-body results for two variants of the curvaton model of inflation: (i) a "tau_NL" scenario in which the curvaton and inflaton contribute equally to the primordial curvature perturbation and (ii) a "g_NL" model where cancellations vanish the usual quadratic f_NL term in the potential, but give rise to a large cubic term.
April 29, 2011 | 12:00 PM | LASR Conference Room | Friday noon seminar Recoiling Black Holes in Merging Galaxies Laura Blecha, Harvard-Smithsonian Center for Astrophysics
Ample evidence suggests that the growth of SMBHs and their host galaxies is closely linked. However, in the event of a merger, gravitational-wave (GW) recoil may displace a SMBH from its galactic center, or eject it entirely. To explore the consequences of this phenomenon, we use hydrodynamic simulations of gaseous galaxy mergers that include GW recoil kicks to the merged BHs. We have conducted a large parameter study with a range of recoil velocities and galaxy merger models, enabling us to identify systematic trends in the behavior of recoiling BHs. Specifically, I will describe our results concerning (i) the dynamics of recoiling BHs in gaseous merger remnants, (ii) their observable signatures, including kinematically- and spatially-offset AGN, and (iii) their effects on the co-evolution of BHs and galaxies, including scatter in the BH-bulge relations and extended starburst phases in the merger remnant.
May 6, 2011 | 12:00 PM | LASR Conference Room | Friday noon seminar The recent observation of the ultra-high energy universe with the IceCube neutrino telescope Aya Ishihara, Chiba University
IceCube is a cubic kilometer scale, deep-ice neutrino detector which had been under construction at the South Pole since January 2005 and the construction was completed in December 2010. IceCube's high energy neutrino search includes the TeV energy region, where atmospheric neutrinos are dominant, and the EeV regime, where ultra-high energy cosmic-ray emissions play leading roles in the flow of astrophysical energies. The 2008-2009 science run with the partially (~50 %) constructed detector has surveyed neutrino emissions with the world's best sensitivity from TeV energies to far beyond. This talk will report the most recent results of observations of the neutrino universe from 1016eV to 1020eV by IceCube. The results constrain the ultra-high energy cosmic-ray radiations at cosmological distances and will be discussed in context of the Fermi-LAT diffuse gamma-ray measurement in the GeV region.
May 13, 2011 | 12:00 PM | LASR Conference Room | Friday noon seminar What to do with 400,000 Astronomers Chris Lintott, Adler Planetarium, University of Oxford
Citizen science - the involvement of volunteers in the analysis of scientific data - has the potential to make a huge impact in this era of widespread broadband and enormous data sets. In this talk, Galaxy Zoo principal investigator Chris Lintott, will tell the story of and review the results from one of the largest distributed projects, which recruited hundreds of thousands of volunteers to provide hundreds of millions of classifications of galaxies drawn from the Sloan Digital Sky Survey and from Hubble Space Telescope surveys. Drawing on education research and game design, the talk will also cover the evolution of the project from Galaxy Zoo to the Zooniverse, a collection of projects which has volunteers hunting for planets, scouring the lunar surface and even examining ancient papyri.
May 20, 2011 | 12:00 PM | LASR Conference Room | Friday noon seminar Modified Gravity makes Galaxies Brighter Eugene Lim, University of Cambridge
Attempts to modify gravity to achieve late time cosmic acceleration usually run into already stringent solar system constraints on general relativity (GR). Recently, it is realized that one can evade these constraints via "screening" -- one construct theories where the effective gravity is dependent on ambient gravitational potential, hence since the solar system is embedded in a deep potential well of the Milky Way and local Group, GR is restored. Meanwhile at cosmological scales, gravity can be modified to resemble dark energy. Such theories include the venerable f(R) gravity theory, and the more recent trendy models such as the Chameleon and the Symmetron. I will show that modified gravity will change the stellar structure equations dramatically in dwarf galaxies not associated with clusters. Stars in these galaxies are generically hotter and more luminous, and live much shorter lives as a result. Not only are the galaxies then brighter, they are also bluer -- allowing us to put new bounds modified gravity by an order of magnitude or more.
May 27, 2011 | 12:00 PM | LASR Conference Room | Friday noon seminar Infrared-luminous galaxies: their evolution, clustering, and fates Benjamin Weiner, Steward Observatory/University of Arizona
Infrared-luminous galaxies are powered by star formation or active galactic nuclei, but emit much of their light as radiation reprocessed by dust into the far infrared. The most massive starbursts in both the local and high redshift universe manifest themselves as ultraluminous infrared galaxies. This class of galaxies was discovered by IRAS and studied extensively with Spitzer. However, it remains controversial what IR-luminous galaxies at z=1 are, and what they will evolve into. Are IR-luminous galaxies at high redshift mostly galaxy mergers, as they are at low redshift? Are ultraluminous IR galaxies strongly clustered, and can we infer whether they must evolve into cluster galaxies today? I will discuss these questions using data from Spitzer/MIPS, HST, and the DEEP2 redshift survey. I will also show near-infrared slitless spectroscopy from the new WFC3 instrument on Hubble, and its application as a probe of star-forming galaxies at high redshifts. Near-IR slitless spectroscopy from space is a technique planned for the WFIRST satellite and prefigures the science it can yield for studying galaxy evolution.
June 3, 2011 | 12:00 PM | LASR Conference Room | Friday noon seminar Using weak lensing to probe the link between galaxies and dark matter Alexie Leauthaud Harnett, Lawrence Berkeley National Lab
I will present a new theoretical framework that combines measurements of galaxy-galaxy lensing, galaxy clustering, and the galaxy stellar mass function in a self-consistent manner. While considerable effort has been invested in exploring each of these dark matter probes individually, attempts to combine them are still in their infancy despite the potential of such combinations to elucidate the galaxy-dark matter connection, to constrain cosmological parameters, and to test the nature of gravity. I will then present an application of this model to the COSMOS data and will show how the stellar-to-halo mass relation evolves from z=1 to z=0. Finally, I will discuss the potential of future weak large surveys for galaxy-galaxy lensing measurements and I will show some early work from a new 170 deg2 weak lensing survey ("CS82") we have recently completed in the Stripe82 equatorial region.
April 12, 2011 | 4:00 PM | KPTC 106 | Special seminar Universe or Multiverse Martin Rees, Astronomer Royal, Cambridge
Martin Rees is Master of Trinity College, Cambridge and holds the honorary title of Astronomer Royal. He was previously Director of the Institute of Astronomy at Cambridge, and has lectured widely in the US, Europe and the Far East. His research interests include cosmology, galaxy formation, black holes and 'high energy' phenomena in the universe. As well as his research publications, he is the author of eight books, and numerous articles on scientific and general subjects. He is a foreign associate of the US National Academy of Sciences, the Russian Academy of Sciences, the Pontifical Academy, and several other foreign academies. He is a member of the UK's House of Lords, and recently completed a five-year term as President of the Royal Society (the UK's national science academy).
April 28, 2011 | 2:00 PM | LASR Conference Room | Open Group seminar PIXIE: A CMB Polarization Measurement Dale Fixsen, U MD/Goddard Space Flight Center
PIXIE is a proposed NASA Midex satellite experiment to measure CMB B-mode polarization. It measures the polarization spectrum from 30GHz to 6THz over the whole sky with 30GHz spectral resolution and 2 degree angular resolution. It also measures the absolute spectrum of the CMB and foregrounds.
May 10, 2011 | 2:00 PM | LASR Conference Room | Open Group seminar Influence of long wavelength modes on local dynamics Tobias Baldauf, University of Zurich
The gravitational coupling between short and long wavelength modes is of essential influence for modern cosmology, for instance for perturbation theory, galaxy biasing and primordial non-Gaussianity. In the case of local non-Gaussianity the high-k behaviour of galaxy clustering is a promising probe for constraints on inflationary physics. This motivated us to revisit the coupling in a general relativistic context making use of Fermi local coordinates. We show that long wavelength modes can be generally interpreted as curved Universes and present a mapping that enables the inclusion of long modes into intermediate scale simulations.