Astrophysics Science Division Colloquium Series
Schedule: Fall 2011
Astrophysics Science Division Colloquium Series
Schedule: Fall 2011
Through the courtesy of the speakers since 2004, some presentations are available on line.
Recent schedules:
ASD Colloquia are Tuesdays at 3:45 pm (Meet the Speaker at 3:30 pm)
in Bldg 34, Room W150
unless otherwise noted.
Gravity and Extreme Magnetism SMEX missionJoe HillGSFCTuesday, September 20, 2011AbstractThe Gravity and Extreme Magnetism SMEX mission will be the first mission to catalogue the X-ray polarisation of many astrophysical objects including black-holes and pulsars. This first of its kind mission is enabled by the novel use of a time projection chamber as an X-ray polarimeter. The detector has been developed over the last 5 years, with the current effort charged toward a demonstration of it's technical readiness to be at level 6 prior to the preliminary design review. This talk will describe the design GEMS polarimeter and the results to date from the engineering test unit. |
Active Galaxy Demography, Physics, and Ecology in the Distant Universe: A Dozen Years of Progress with Ultradeep Chandra SurveysNiel BrandtPenn State UniversityTuesday, September 27, 2011AbstractExtragalactic X-ray surveys over the past dozen years have dramatically improved understanding of the majority populations of active galactic nuclei (AGNs) over most of the history of the Universe. I will present results from ultradeep surveys with the Chandra X-ray Observatory, such as the Chandra Deep Fields, highlighting some of the exciting findings about AGN demography, physics, and ecology. I will discuss studies of highly obscured AGNs at z = 0.5-1 as well as through the galaxy formation era at z = 1-4. I will also describe constraints upon the co-evolution of supermassive black holes and massive galaxies set via studies of AGN host colors, magnitudes, and masses. I will end by describing some key unresolved questions and future prospects. |
VERITAS Observations of the Crab and Other Cosmic-Ray AcceleratorsMartin SchroedterSAOTuesday, October 4, 2011AbstractVERITAS is an astrophysical gamma-ray detector with excellent sensitivity between 0.1 and 50 TeV. It consists of four 12-meter imaging atmospheric Cherenkov telescopes located near Tucson, AZ, and in its fourth full year of operation, VERITAS is studying the most extreme astrophysical accelerators in the Universe: supernova remnants, binary systems, starburst galaxies, GRBs, AGN and massive stars. The Crab was the first confirmed source of TeV gamma rays and until recently was considered a steady "candle" with no indication of flickering nor any pulsation. The improved sensitivity provided by VERITAS and a deep exposure of the Crab has revealed pulsed emission above 100 GeV. This discovery challenges existing theories, requiring both the location and acceleration mechanism to be reconsidered. I will discuss the measurements in the context of measurements made by Fermi space telescope below 10 GeV. |
The Co-Evolution of Galaxies & Black Holes: Clues in the Modern UniverseTim HeckmanJohns Hopkins UniversityTuesday, October 11, 2011AbstractI will summarize our current understanding of the relationship between the evolution of black holes and galaxies in the local universe. I will show that the growth of super-massive black holes as traced by optically luminous active galactic nuclei is strongly linked to the on-going formation of stars in the bulge component of galaxies. It is likely that this co-evolution is driven by the accretion and radial transport of cold gas, but major mergers of galaxies are not the primary mechanism for doing this. I will show that the fueling source for the black hole growth is likely to be mass loss from intermediate mass stars. I will show that the characteristic mass scales for the populations of growing black holes and bulges are substantially lower now than in the past. The most massive black holes are largely quiescent today with low-level activity driven by the slow accretion of gas shed by evolved stars. The weak radio jets such black holes produce nonetheless may play a key role in suppressing star formation, keeping their surrounding host galaxy "red and dead". Evidence for galaxy-scale feedback in the form of powerful AGN-driven outflows in the strongly accreting radio-quiet black holes is not clear in typical active galactic nuclei today. However, feedback from the massive stars whose formation accompanies the growth of the black hole can be significant. |
Probing Nearby Planetary Systems by Debris Disk ImagingKarl StapelfeldtNASA/GSFCTuesday, November 1, 2011AbstractMany main-sequence stars possess tenuous circumstellar dust clouds believed to trace extrasolar analogs of the Sun's asteroid and Kuiper Belts. While most of these "debris disks" are known only from far-infrared photometry, a growing number of them are now spatially resolved. In this talk, I'll review what is currently known about the structure of debris disks. Using images from the Hubble, Spitzer, and Herschel Space Telescopes, I will show how modeling of these resolved systems can place strong constraints on dust particle properties in the disks. Some of the disks show disturbed structures suggestive of planetary perturbations: specific cases will be discussed where directly-imaged exoplanets are clearly affecting debris disk structure. I'll conclude with thoughts on the future of high contrast exoplanet imaging. |
Searching for redshift 7 quasars with the UKIRT Infrared Deep Sky SurveyDaniel MortlockImperial CollegeTuesday, November 8, 2011AbstractQuasars are powerful probes of the early Universe, although it has not previously been practical to search for quasars beyond a redshift of z > 6.5 because they have been identified primarily in optical surveys. Using data from the UKIRT Infrared Deep Sky Survey (UKIDSS), it has been possible to search beyond this optical limit, resulting in the discovery of a dozen high-redshift quasars including one, ULAS J1120+0641, at a redshift of z = 7.085. ULAS J1120+0641 hosts a 2x109 M_Sun black hole, the existence of which just 0.8 Gyr after the Big Bang places significant restrictions on the possible models of black hole growth. The small visible size of the ionized "near zone" around the quasar, combined with a Ly alpha transmission profile that is consistent with a damping wing, provide strong evidence that the neutral fraction of the inter-galactic medium immediately in front of the quasar was greater than 10 per cent. |
Life on the Edge: Planetary Atmospheres in Extreme EnvironmentsHeather KnutsonUniversity of California BerkeleyTuesday, November 15, 2011AbstractThe past decade has marked a period of great progress in our quest to discover and characterize the properties of the planets outside of our own solar system. A majority of the planets observed to date have properties that are distinctly different from those of the solar system planets; for instance, "hot Jupiters" are a class of gas giant planets orbiting at distances of less than 0.05 A.U. from their host stars. As a result of their short orbital periods we expect that these planets should be tidally locked, potentially leading to dramatic variations in both temperature and composition between the day- and night-side hemispheres. In my talk I will discuss how these exotic worlds serve as a testbed for our understanding of the physical processes that shape planetary atmospheres, which can in turn impact our ability to accurately predict the properties of smaller and cooler planets. I will present multi-wavelength Spitzer observations of the infrared emission spectra of a representative sample of hot Jupiters as a function of orbital phase, and discuss the resulting implications for their atmospheric properties. I will then close with a look ahead at the prospects for applying these same techniques to characterize the atmospheres of smaller and cooler planets. |
Quasar Absorption Lines as Probes of Galaxy EvolutionVarsha Kulkarni(University of South CarolinaTuesday, November 29, 2011AbstractThe evolution of galaxies and the cosmic history of element production are fundamental themes in modern astrophysics and cosmology. However, the light emitted by distant galaxies is often too faint to allow detailed studies. Absorption lines in quasar spectra can be used to probe interstellar gas in galaxies at various stages of evolution, and thus provide powerful probes of the history of star formation and chemical enrichment in galaxies. Using this technique, we have uncovered a ``missing metals problem'' in low-redshift galaxies, i.e. a discrepancy between the observed amount of metals and the amount predicted by the chemical evolution models. On the other hand, there appears to be a population of galaxies with very high levels of metals, including some that had reached several times the Sun's metallicity 7-10 billion years ago! What are these galaxies, and why did they get enriched so quickly? We will discuss clues emerging from our imaging/ spectroscopic observations that promise to shed light on various aspects of galaxy evolution. Finally, we will discuss observations of interstellar dust in the quasar absorbers, and implications for dust composition in distant galaxies. |
LIGO: Searching for the most violent events in the Universe at the attometer levelDave ReitzeCaltechTuesday, December 6, 2011AbstractThe detection of gravitational waves will open up a new 'dark' window into the universe later this decade. In this colloquium, I'll talk about gravitational waves and what makes them so interesting and challenging to detect, how we search for them using Really Big interferometers, as well as the results of LIGO's science runs to date and the prospects for multi-messenger astronomy from the coming second generation global gravitational-wave network. |
The Quest for the Dynamical Signature of Close Supermassive Binary Black HolesMike EracleousPenn State UniversityTuesday, December 13, 2011AbstractSupermassive binary black holes (masses of order 1 million to 1 billion solar masses and separations less than 1 pc) are predicted to be an inevitable late stage in the evolution of galaxy mergers. Such binaries have also been invoked as explanations of the formation of the cores of elliptical galaxies following a merger and the mass deficits therein, the apparent precession of radio jets, and the formation of X-shaped radio sources and they are predicted to be prime sources of gravitational waves. Yet, they remain elusive. After a historical introduction, I will describe a systematic search for such objects using the SDSS spectroscopic database and the followup observations of the initial candidates. I will present the first results from this search and discuss critical tests of the methodology as well as plans for future work. |
Judith Racusin