List of Past Astronomy Colloquia : 01-Sep-2009 to 31-Dec-2009


Date:   Wednesday 02-Sep-2009
Speaker:   Prof. Andrew Baker (Rutgers University)
Title:  "Star Formation in Lyman Break Galaxies, Near and Far"

Large samples of star-forming galaxies at high redshift, including "Lyman break galaxies" (LBGs) at z~3, can be selected on the basis of their distinctive rest-frame UV colors. Such UV-selected samples have provided important insights about the properties and histories of high-redshift galaxies; however, due to individual systems' faintness at long wavelengths, we still have relatively little information about the details of how they are turning gas into stars. I will discuss two strategies for improving our understanding of star formation in LBGs and their ilk: observing gravitationally lensed systems at high redshift, and observing their unlensed (but very rare) close analogs at low redshift. I will use this discussion to address the important question of whether radio astronomers are necessary.


Date:   Wednesday 09-Sep-2009
Speaker:   Prof. Eric Bell (University of Michigan)
Title:  Old, Red and Dead Galaxies in a Lambda CDM Universe

Roughly half of all stars reside in 'old, red and dead' galaxies. These galaxies form stars at very low rates, have little cold gas and typically have a dominant stellar spheroid supported by random motions. In this talk, I will review the evolution of the old, red and dead early-type galaxy population, demonstrating that there is growth in this population between z~1 and the present day. I will show that this build-up affects even the most massive galaxies, although in that case the degree of growth in the population is substantially less certain. In both cases, I will argue that galaxy merging in the amount naturally predicted in a cosmological framework is a key (but by no means the only) driver of that evolution.


Date:   Tuesday 15-Sep-2009
Speaker:   Prof. Stacy McGaugh (UMD)
Title:  "Gravity and Dark Matter in the Universe"

Astronomical observations now constrain the parameters of cosmology to unprecedented precision. Many lines of evidence indicate the presence of a novel form of non-baryonic dark matter that permeates the cosmos and outweighs normal baryonic matter by roughly 5:1. As yet, there is no persuasive laboratory detections of these hypothesized dark matter particles. An alternative hypothesis is that instead of dark matter, fundamental duynamical laws need revision at very low accelerations. I will discuss the evidence for and against these ideas. Physics Colloquiua are preceded by light refreshments at 3:30pm.


Date:   Wednesday 16-Sep-2009
Speaker:   Prof. Chris Done (Durham University)
Title:  "Black Hole Accretion Flows: spectra and variability!"

I will describe a physical model for the observed X-ray spectra and variability in black hole accretion flows. This is based on the truncated disc, hot inner flow geometry, where the truncation radius of the thin disc decreases as the mass accretion rate increses until the disc reaches the last stable orbit. I will show that (MRI) turbulence in this hot flow can match the broad band continuum noise power spectral shape, while the strong, low frequency Quasi-Periodic Oscillation (QPO) can be formed from Lense-Thirring precession of the hot flow. However, this low frequency QPO is probably *not* the counterpart of the, so far unique, AGN QPO seen in RE J1034+396. I will show instead how this is more probably related to a higher frequency (67 Hz) QPO seen in the super Eddington black hole GRS1915+105.


Date:   Wednesday 23-Sep-2009
Speaker:   Dr. Fred Lamb (University of Illinois)
Title:  High-Frequency X-ray Oscillations from Neutron Stars: Probing Dense Matter and Strong Gravity

Using NASA’s RossiXTE satellite, astronomers have discovered that disk- accreting neutron stars with weak magnetic fields produce three distinct types of nearly periodic high-frequency X-ray oscillations. Two are powered primarily by conversion of gravitational binding energy into heat at the stellar surface. The third is powered by sudden nuclear burning of accreted matter. All three oscillations are affected by the strong gravitational field of the star. They are being used to explore fundamental physics, such as strong-field gravity and the properties of matter under extreme conditions, as well as important astrophysical questions, such as the formation and evolution of neutron stars. These studies have narrowed the possible descriptions of ultradense matter and revealed that dozens of neutron stars have very high spin rates and dynamically important magnetic fields. Analysis of the highest-frequency oscillations has provided the first evidence for the existence of the innermost stable circular orbit around compact massive objects that is predicted by strong-field general relativity. The magnetic fields of these neutron stars are strong enough that they are expected to become millisecond radio- emitting pulsars when accretion ceases.


Date:   Wednesday 30-Sep-2009
Speaker:   Dr. Maura McLaughlin (WVU)
Title:  TBA


Date:   Wednesday 7-Oct-2009
Speaker:   Dr. Eric Smith (NASA Headquarters)
Title:  NASA's Astrophysics Program

I will provide an overview of NASA's astrophysics portfolio, including current and planned space missions, research support program, and details of the suborbital and technology development opportunities. I will also review the federal budget process, the President's Fiscal Year 2010 budget request for NASA's Astrophysics Division, and programmatic guidance offered to the Astro2010 Astronomy & Astrophysics decadal survey.


Date:   Wednesday 14-Oct-2009
Speaker:   Dr. Jian Ge (Florida)
Title:  The SDSS-III Multi-object APO Radial-Velocity Exoplanet Large-area Survey

I will present results from the on-going Multi-object APO Radial-Velocity Exoplanet Large-area Survey (MARVELS) as part of the SDSS-III program. The survey is to monitor a total of 11,000 V=8-12 FGK stars over ~800 square degrees over the 6 years to produce a large, statistically well defined sample of giant planets (~200) with a wide range of masses (0.2-15 Jupiter masses) and orbits (1 day-2 years). These planet samples will be used for studying the diversity of extrasolar planets and constraining planet formation, migration & dynamical evolution of planetary systems and identifying signposts for lower-mass or more distant planets.


Date:   Wednesday 21-Oct-2009
Speaker:  
Title:  NO COLLOQUIUM


Date:   Wednesday 28-Oct-2009
Speaker:   Dr. Norm Murray (University of Toronto)
Title:  Stellar Feedback and Galaxy Formation

Star formation in galaxies is remarkably inefficient; naively one might expect that gas would cool rapidly, and collapse to form stars on a dynamical time. Observations, on the other hand, show that only two percent of the gas in a galaxy is turned into stars per dynamical time. Similar comments apply to star formation in individual giant molecular clouds. In the case of galaxies, current models attribute the low efficiency to turbulence induced by energy input from supernovae. In giant molecular clouds, the low efficiency is attributed to turbulent stirring by ionized gas (HII regions or shocked stellar winds). I will argue that the low efficiency in both cases is driven primarily by radiation pressure, from light produced by massive star clusters, on dust. I will present models that reproduce the Carina and Westerlund I clusters in the Milky Way, the 20 or so massive clusters in M82, and even more massive clusters, with masses up to 100 million solar masses, that dominate the dynamics of the ISM in ultraluminous galaxies like Arp 220. If time permits, I will discuss winds from such clusters.


Date:   Wednesday 04-Nov-2009
Speaker:   Dr. Gerhardt Meuerer (JHU)
Title:  Star Formation Laws in HI Selected Galaxies

Star formation is complex, and very hard to model even with the fastest computers. Instead, simulations of galaxy evolution usually resort to emprical based prescriptions to set the amount of ISM that is converted into stars (the Star Formation Law - SFL) and the mass distribution of stars formed (the Initial Mass Function - IMF). These "laws" have proved remarkably resilient, having been proposed over 50 years ago. I will show results from the Survey of Ionization in Neutral Gas Galaxies (SINGG) and the Survey of Ultraviolet emission in Neutral Gas Galaxies (SUNGG) which survey the star formation properties of galaxies as traced by H-alpha and Ultraviolet emission. Our simple neutral hydrogen (HI) only selection criteria results in a sample that captures all types of star forming galaxies, while the use of two star formation tracers and integrated HI fluxes provide new constraints on both the SFL and IMF. We find strong correlations between the Halpha/FUV flux ratio and the optical surface brightness of galaxies. The only plausible explanation of this result is that the IMF is not constant. This result has enormous implications for galaxy evolution. Meanwhile strong correlations between the HI, star-formation, and old stellar population properties of galaxies are tighter than the Kennicutt-Schmidt SFL. The existence of an HI - star formation connection has been somewhat of a mystery since stars form in the molecular not the neutral ISM, while the highest mass stars and the HI have very different distributions in galaxies. I will argue that the IMF and the other star formation scaling relations result from pressure-regulated star-formation in a disk maintained at near critical dynamical stability.

I will show results and ongoing work from the Survey of Ionization in Neutral Gas Galaxies (SINGG) and the Survey of Ultraviolet emission in Neutral Gas Galaxies (SUNGG) which survey the star formation properties of galaxies as traced by H-alpha and Ultraviolet emission, respectively. Our simple HI only selection criteria results in a sample that captures all types of star forming galaxies, while the use of two star formation tracers gives us sensitivity to the Initial Mass Function. Our team has found strong correlations between the Halpha/FUV flux ratio and the optical surface brightness of galaxies. The only plausible explanation of this result is that the IMF is not constant. This result has enormous implications for galaxy evolution in both the near and distant universe. Our sample also shows strong correlations between the HI, star-formation, and old stellar population properties of galaxies. These scaling relations are tighter than the Kennicutt-Schmidt Star Formation Law. The existence of an HI - star formation connection has been somewhat of a mystery since stars form in the molecular not the neutral ISM, while the highest mass stars and the HI have very different distributions in galaxies. I will argue that the IMF and the other star formation scaling relations result from pressure-regulated star-formation in a disk maintained at near critical dynamical stability.


Date:   Wednesday 11-Nov-2009
Speaker:   Dr. Jason Tumlinson (STScI)
Title:  "The First Stars and the Fossil Record"

Understanding the first stars and galaxies is a major goal of astrophysics now and in the coming decade. We now recognize that the truly first stars may lie beyond the view even of JWST, so I am investigating how we can use the "fossil record" of star formation preserved in old, extremely metal-poor stars in the Milky Way to probe star formation in the first few billion years of cosmic time. I will describe the new type of chemical evolution modeling developed to study this fossil record, evaluate several places where the record of the first stars can be sought, and speculate about what we might find out when we look there.


Date:   Wednesday 18-Nov-2009
Speaker:   Dr. Adam Leroy (NRAO)
Title:  Where is the Interstellar Medium Good at Forming Stars?

I will discuss what recent multiwavelength surveys tell us about why stars form where they do in galaxies and what makes the ISM good at forming stars. The question is an open one, with results in the last few years variously identifying gravitational stability, metallicity, pressure, opacity, and collisions in the ISM as the regulating quantity. From large programs with the IRAM 30m ("HERACLES") and the VLA ("THINGS") we know the distribution of atomic and molecular gas in several dozen galaxies that have also been observed by Spitzer and GALEX. These data allow us to estimate a range of physical conditions over kiloparsec-sized resolution elements across each galaxy (e.g., the star formation rate, HI mass, H2 mass, stellar mass, kinematics, dust-to-gas ratio). We are using these estimates to push beyond galaxy-averaged scaling relations, testing proposed local drivers for the formation of molecular clouds and stars from diffuse neutral gas. I will summarize these tests and give our current best answers to the basic question: "where is the interstellar medium good at forming stars?"


Date:   Wednesday 25-Nov-2009
Speaker:  
Title:  NO COLLOQUIUM


Date:   Wednesday 2-Dec-2009
Speaker:   Dr. Bret Lehmer (GSFC)
Title:  New Results from a Deep Chandra Observation of the SSA22 Protocluster at z = 3.09

ABSTRACT: It is now widely accepted that the growth of galaxies and their central supermasive black holes (SMBHs) are linked. Observations and CDM theories of large scale structures indicate that galaxy growth is accelerated in high-density environments, and the highest density structures underwent their most vigorous star formation at z > 2--3. To study the corresponding growth of SMBHs in such high-density environments, we have conducted a deep ~400 ks Chandra survey covering the SSA22 protocluster at z=3.09: the Chandra Deep Protocluster Survey. The protocluster itself contains a factor of ~6 overdensity in galaxies (i.e., LBGs and LAEs) and is predicted to collapse into a z=0 cluster resembling a rich local cluster (e.g., Coma). I will report on the current status of the Chandra Deep Protocluster Survey and will highlight two recent investigations that make use of the new Chandra data. These investigations include (1) a study of how the growth of galaxies and SMBHs depends on environment in the z=3 Universe, and (2) a comprehensive exploration of the role that AGN and star-formation activity play in the production of enigmatic extended (>30 kpc) Lyman-alpha emitting blobs (LABs) that are found in excess in the protocluster.


Date:   Wednesday 9-Dec-2009
Speaker:   Dr. Geoffrey Bower (Berkeley)
Title:  Wide Field Transient Surveys

The time domain of the radio wavelength sky has been only sparsely explored. Nevertheless, recent discoveries from limited surveys and serendipitous discoveries indicate that there is much to be found on timescales from nanoseconds to years and at wavelengths from meters to millimeters. These observations have revealed unexpected phenonmena such as rotating radio transients and coherent pulses from brown dwarfs. Additionally, archival studies have revealed an unknown class of radio transients without radio, optical, or high-energy hosts. The new generation of centimeter-wave radio telescopes such as the ATA, SKAMP, and ASKAP will exploit wide fields of view and flexible digital signal processing to systematically explore radio transient parameter space, as well as lay the scientific and technical foundation for the SKA. Known unknowns that will be the target of future transient surveys include orphan gamma-ray burst afterglows, radio supernovae, tidally-disrupted stars, flare stars, and magnetars. While proving the variable sky, these surveys will also provide unprecedented information on the static radio sky. I will present results from three ATA surveys: the Fly's Eye survey, the ATA Twenty CM Survey (ATATS), and the Pi GHz Survey (PiGSS).


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