List of Past Astronomy Colloquia : 01-Jan-2011 to 01-Jun-2011

Date:   Wednesday 02-Feb-2011
Speaker:   Dr. Tim Heckman (JHU)
Title:  "Local Starbursts in a Cosmological Context"

Local starburst galaxies provide excellent laboratories in which to undertake detailed investigates of the physical processes at work in typical galaxies in the early universe. In this talk I will describe the basic properties of starbursts and relate these properties to a number of major issues in galaxy formation and evolution. I will specifically highlight the effects of global feedback from massive stars, the reionization of the universe, and the co-evolution of galaxies and supermassive black holes.

Date:   Wednesday 09-Feb-2011
Speaker:   Dr. Jonathan Tan (University of Florida))
Title:  Star formation rates of disk galaxies and circumnuclear starbursts

Star formation is highly localized, occurring within particular, parsec-scale regions of giant molecular clouds (GMC). On the other hand, there appear to be correlations between galactic-scale gas inventories, dynamical timescales and star formation rates. I review the physical processes that may be driving star formation activity, including turbulence, large-scale dynamical instabilities, and converging flows created by GMC collisions. I discuss recent theoretical and observational work to distinguish these possibilities. The former includes analytic theory to understand GMC collision rates and large-scale numerical simulations of disk galaxies and star cluster formation. The latter includes infrared studies of dense, cold regions of GMCs - the so-called infrared dark clouds - and a large, unbiased survey of dense gas in the Milky Way to probe the demographics of star cluster formation. The most extreme star formation rates are found in circumnuclear starbursts, such as in Arp 220. I describe how these systems may be understood by a unified, self- similar model of star formation in disk systems.

Date:   Wednesday 16-Feb-2011
Speaker:   Dr. Massimo Stiavelli (StSci)
Title:  Observing the epoch of reionization with the Hubble and James Webb Space Telescopes

I will review recent observational results on the highest redshift objects discovered with the Wide Field Camera 3 on the Hubble Space Telescope. After discussing the implications of these discoveries for the reionization of Hydrogen and the early evolution of galaxies I will give an overview of theoretical results on the first galaxies and discuss their observability with Hubble's successor: the James Webb Space Telescope. I will end by presenting a status of the Webb Telescope.

Date:   Wednesday 23-Feb-2011
Speaker:   Dr. Paul Demorest (NRAO)
Title:  Testing Fundamental Physics with Radio Pulsars

Millisecond radio pulsars provide us with unique astronomical "laboratories" for exploring fundamental physics in a variety of ways -- from the physics of matter at super-nuclear density, to experimental tests of gravity, to the possible direct detection of gravitational radiation. In this talk, I will focus on our recent discovery of a two solar mass pulsar, currently the highest well-measured neutron star mass. In addition to several astrophysical implications, this measurement places strong constraints on theories of neutron star composition via the nuclear matter equation of state.

Date:   Wednesday 02-Mar-2011
Speaker:   Dr. Rychard Bouwens (Leiden Observatory)
Title:  Galaxy Build-up and Evolution at z>=7: Early results from ultra-deep WFC3/IR observations over the HUDF and GOODS

The new WFC3/IR camera aboard HST enables us to survey the sky in the near-IR 40x more efficiently than ever before -- allowing for enormous progress in searches for z>=7 galaxies. Already in the first year of observations, we have deep and ultra-deep observation over 52+ arcmin**2 in legacy fields like the HUDF and GOODS. With these data, we have been able to select 80+ z~7 galaxies, 60+ z~8 galaxies, and even possible z~10 galaxies. These new selections have allowed us to quantify the evolution of the UV LF and faint-end slope from z~10, significantly constrain the stellar populations and dust properties of z~5-8 galaxies, and construct a general picture of how galaxies build up early in the universe. In this presentation, I provide a summary of some of our early results.

Date:   Wednesday 09-Mar-2011
Speaker:   Dr. Rosemary Wyse (JHU)
Title:  Extremely Metal-poor Stars in the Milky Way and its Satellite Galaxies

I will present results on the population of stars with extremely low values of iron abundance, including those with less than one-thousandth of the solar value, in both the Milky Way's field stellar halo and satellite systems. I will discuss elemental abundances, and their implications for the stellar IMF and star formation at early epochs.

Date:   Wednesday 16-Mar-2011
Speaker:   Dr. Hector Arce (Yale University)
Title:  Stellar feedback during the early stages of star formation and its effect on the environment

Young stars go through a mass-loss process during the early stages of their lives. They drive winds that deposit energy and momentum into their surroundings and have a considerable impact on the dynamics, distribution, and chemical composition of the gas in star-forming clouds. Collimated outflows as well as wide-angle winds originate within a few AU (or less) of the forming star and may reach parsec-scale sizes. Thus, they interact with a variety of environments in the interstellar medium, from the high-density envelope surrounding the protostar to the low-density atomic medium surrounding the parent molecular cloud. I will discuss the importance of outflow impact on molecular clouds and the star formation process at different evolutionary stages ---from the very early, so-called, first hydrostatic core phase to the pre-main sequence (T Tauri) stage--- in both isolated sources and clustered regions. I will also briefly touch on how studying outflows allows to improve our understanding of the infall and accretion processes in young stars.

Date:   Wednesday 23-Mar-2011

Date:   Wednesday 30-Mar-2011
Speaker:   Dr. Greg Madejski (Stanford University)
Title:  "The Fermi Observatory View of the Gamma-ray Sky."

Fermi Gamma-ray Space Telescope has been operating for nearly three years, and is providing excellent data for celestial gamma-ray sources, but it is also capable of measuring the spectrum of cosmic-ray electrons. This presentation will highlight the recent results from Fermi's Large Area Telescope, and will cover new insight resulting from the measurements of gamma-ray properties of rotating neutron stars (pulsars), supernova remnants, and gamma-ray bursts; it will cover in more detail the new insights gleaned from observations of relativistic jets in active galaxies.

Date:   Wednesday 06-Apr-2011
Speaker:   Dr. Snezana Stanimirovic (U. Wisconsin-Madison)
Title:  Galaxy evolution begins at home: GALFA, 21-SPONGE and GASKAP

While studies of galaxy evolution generally focus on extensive HI surveys at large redshifts, understanding of detailed physical processes that drive HI evolution within galaxies is equally important. Specifically, I focus on three open questions regarding the very first step in the star-formation cycle in galaxies: What are the basic properties of the warm neutral gas, the progenitor of cold star-forming clouds? What are the origin and level of interstellar inhomogeneities as seeding agents for molecule and star formation? And, what processes control the ratio of atomic to molecular gas? The very local Universe offers an unparalleled high-resolution view for answering these questions and current and upcoming radio telescopes (e.g. Arecibo, EVLA, ASKAP) promise great advances.

Date:   Wednesday 13-Apr-2011
Speaker:   Dr. Rosalba Perna (U. Colorado)
Title:  Gamma-Ray Bursts in the Swift Era: Impact for Cosmology

Gamma-Ray Bursts (GRBs) are the brightest light sources in the Universe, as well as the most distant sources known. These characteristics, combined with their powerlaw spectra, make them ideal cosmological probes. In this talk I will discuss how GRBs are impacting several areas of cosmology. In particular, I will show how they can be used to trace the evolution of the mean density and clumpiness of the interstellar medium with redshift, and the properties of dust in high-z galaxies. Detection of GRBs at very high redshifts can help set constraints on the small-scale power spectrum of density fluctuations. High-resolution observations of long GRBs allow to shed light on the properties of their massive star progenitors. Statistical studies of short GRBs can improve our understanding of evolutionary binary scenarios.

Date:   Wednesday 20-Apr-2011
Speaker:   Dr. Alice Shapley (UCLA)
Title:  Narrowband Imaging Observations of Lyman-Continuum Radiation at z~3

Determining the contribution of galaxies to the reionization of the universe is a fundamental goal for studies of the intergalactic medium (IGM), and galaxy formation and evolution. A direct measurement of ionizing Lyman-continuum radiation escaping from galaxies is not possible at the epoch of reionization, due to the high optical depth of the IGM, and therefore observations of this process at slightly lower redshift are crucial for understanding what happens at z~6. Building on previous spectroscopic detections of escaping Lyman-continuum radiation, I present new results based on narrowband imaging. The high level at which especially the faintest objects are detected challenges standard models for the escape of ionizing radiation from galaxies. Furthermore, the detailed relationship between the spatial distribution of ionizing and non-ionizing radiation will provide important insights into the process through which ionizing radiation escapes. These new measurements provide a crucial ingredient for models of reionization.

Date:   Wednesday 27-Apr-2011
Speaker:   Dr. Dave Charbonneau (Harvard)
Title:  The Fast Track to Finding an Inhabited Exoplanet

When exoplanets pass in front of their stars, we can estimate their densities and undertake studies of their atmospheres. Such systems have profoundly impacted our understanding of giant exoplanets akin to Jupiter or Neptune, but the study of smaller, rockier, and potentially life-bearing exoplanets has only just begun. By targeting nearby small stars, humble ground-based telescopes could discover super-Earths with temperatures appropriate for liquid water. By differencing spectra gathered when the planet is in view from those when it is occulted by the star, we could study the atmospheres of these worlds to search for the molecular fingerprints of life on the surface below.

Date:   Wednesday 04-May-2011
Speaker:   Dr. Dan Durda (Southwest Research Institute)
Title:  "Ejecta blocks as tracers of the formation and evolution of asteroid regoliths"

Regoliths on small bodies represent valuable natural laboratories for evaluating various models of impact cratering processes since they may present crater structures or ejecta features that either do not form or are hidden on higher-gravity bodies like the Moon. Quantifying the extent to which impact processes generate and redistribute regoliths on small body surfaces is pivotal to the issue of how to relate meteoritical samples to their asteroidal parent bodies and a better understanding of the processes at work in these unique environments is crucial for designing technologies and techniques for future robotic and human exploration, resource utilization, and impact hazard mitigation. Ejecta blocks represent the coarsest fraction of small body regoliths and are important, readily-visible 'tracer particles' for crater ejecta blanket units that may be linked back to specific source craters, thus yielding valuable information on physical properties and constraining various aspects of impact cratering in low-gravity environments. These blocks, launched from the surface of a small, rapidly-rotating, and highly-elongated and irregularly-shaped body, are subjected to a complex dynamical process. Dynamical models of reaccretion of impact ejecta on asteroids thus provide important and necessary tools for a detailed investigation of the distribution and morphology of blocks and finer regolith across their surfaces.

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