Talks & Events
Astronomy Colloquia: 2008
Deciphering the Gamma-ray Sky: GeV Astronomy in the Era of GLAST
The GeV sky was first studied in detail by the Energetic Gamma-Ray Experiment Telescope (EGRET) in the 1990s. Together with an impressive array of data on high-energy systems, the legacy of the EGRET mission includes persisting puzzles, such as the nature of the many yet-unidentified gamma-ray sources, the details of the mechanism producing the Galactic diffuse emission, and the origin of the diffuse, isotropic, persumably extragalactic gamma-ray background. The launch of the Gamma-ray Large Area Space Telescope in the summer of 2008 will once again open the GeV-window of energies to observations, with unprecendented sensitivity and angular resolution. I will discuss recent progress, using model-independent approaches, on the interconnected questions of unidentified sources and the gamma-ray diffuse backgrounds, as well as novel tests that GLAST will enable us to perform to constrain models of nonthermal high-energy processes in Galactic and extragalactic scales.
Dynamics of Protoplanetary Disks: Vortices and Turbulence
Protoplanetary disks are gaseous accretion disks around young stars. I will show how, in hydrodynamical accretion disks such as these, vortices form out of a nonlinear instability. I will also show that a vortex's ultimate fate in 3D depends on whether it is weak or strong. Weak vortices live essentially forever. Strong vortices decay into turbulence via a 3D instability. One interesting implication is that in protoplanetary disks dust can be trapped by weak vortices, triggering planet formation. A second implication is that strong vortices can be responsible for the turbulence that makes these accretion disks accrete.
Star Formation and Gasdynamics in the Nuclear Regions of Galaxies
How are active galactic nuclei (AGNs) and supermassive black holes (SMBHs) fed? To feed them in the absence of major mergers suggests that gas must be transported from kpc-scales the 100s of parsec scales to parsec and sub-parsec scales. I will discuss two interesting cases that might shed light on some of the relevant physics: the formation of the young stellar disk in the nuclei of M31 and the formation of star clusters in the nuclear rings of galaxies. In the case of M31, I will show how a preexisting eccentric stellar disk can radially transport gas on parsec scales, which is reflected in the morphology of the young stellar disk. In the case of star clusters in nuclear rings, tidal interactions between the clusters and the ring result in their separation. The physics of these systems may help elucidate the mechanism by which AGNs and SMBHs are fed.
At the horizon: Imaging black holes and testing General Relativity
We are now at the advent of a golden age for observational tests of strong-field General Relativity. Gravitational wave experiments such as LIGO and LISA have promised to provide extraordinary insights into the structure and evolution of compact objects. However, I will discuss a more modest, complementary approach: directly imaging the horizons of nearby super massive black holes. Such observations are already technically feasible and demonstration experiments are presently underway. I will describe how such experiments can be used to address outstanding problems in black hole astrophysics, provide evidence for the existence of horizons and directly verify that the Kerr metric provides an appropriate description of the spacetime around black holes.
Probing the Turbulence Dissipation Range and Magnetic Field Strengths in Molecular Clouds
I will present a study of the turbulent velocity dispersion spectra as a function of length scale for the coexistent HCN and HCO+ molecular species in the M17 star-forming molecular cloud. I will show that the observed downward shift of the ion's spectrum relative to that of the neutral is readily explained by the existence of an ambipolar diffusion range within which ion and neutral turbulent energies dissipate differently. I will also demonstrate how these observations can be used to evaluate this decoupling scale and estimate the strength of the plane-of-the-sky component of the embedded magnetic field in a completely novel way.
Kepler's Cosmology and Proof of the Heliocentric Theory
Mapping the Dark Universe with Absorption Line Spectroscopy
I will discuss what we have learned about the intergalactic medium and interstellar medium in the young universe through absorption line spectroscopy of distant sources.
Preliminary SNLS 3rd Year Results
The Supernova Legacy Survey (SNLS) is primarily designed to measure the Dark Energy "equation of state parameter" w. The measurement relies on determining the brightness of supernovae with redshift. The goal is to obtain a precision of about 5% in w, which requires controlling flux measurement errors to a level of about 2%. A secondary goal is to be able to characterize the supernova host galaxy population to better understand the astrophysics of supernovae. The SNLS photometric data is obtained from four color, "every 5 nights" images taken with the Megaprime Camera at the CFHT. Spectra to type the supernovae and obtain redshifts are acquired at Gemini, VLT and Keck. Better methods, combined with more data, allow us to reduce our statistical error by about one third from our first year results. Allowance for systematic errors both increases the errors and shifts the point of best fit. A current complication is the necessity to compare to low redshift measurements in the Landolt photometric system, which will be greatly reduced once low redshift data in the SDSS system become available. These measurements are complementary to the CMB and BAO measurements and lead to improved constraints on cosmology.
Binary Compact Objects and their Powerful Astrophysics
Close binary systems harboring two compact objects play a prominent role in a wide range of astrophysics areas, powering some of the most energetic events in nature. In this talk I will highlight their prominence in the context of gravitational-wave searches and the quest for uncovering the origin of gamma-ray bursts. I will review our current understanding of the formation frequency of binary compact objects, their expected gravitational-wave signatures and the challenges facing gravitational-wave astronomy. I will also discuss how studies of formation and evolution of binary compact objects couple to the star formation history in the nearby Universe and potentially provide an explanation of current gamma-ray burst observations.
The Formation and Evolution of a Cosmological Population of Black Holes and Galaxies
There is a growing observational evidence for a close connection between the formation and evolution of galaxies and of their central supermassive black holes. Motivated by this connection, we investigate the coupled formation and evolution of black holes and galaxies using state-of-the-art cosmological hydrodynamic simulations of structure formation in the Lambda-Cold Dark Matter model. Along with the gravitational evolution of dark matter, gas dynamics, cooling and star formation, the simulation follows black hole growth and associated feedback self-consistently. I will discuss black hole growth in the centers of galaxies and the impact of AGN feedback on different aspects of galaxy formation.
The growth of Large-scale Structure from a perspective of 25 years: from CFA1 to DEEP2
25 years ago we thought we knew quite a bit about galaxy clustering, but the first redshift surveys showed just how primitive our knowledge was. In the intervening years enormous changes in technology have made it possible to greatly advance our understanding of large-scale structure, and I will briefly review the the advance of knowledge from my personal perspective. I summarize the recent progress made with the DEEP2 survey on the Keck telescope, a fantastic tool to study galaxies, and galaxy clustering, at redshift one. We have now finished this survey, and as expected from the collection of enormous data sets, we find many unanticipated surprises.
New Measurements of the Hubble Constant and Dark Energy
The Dark Energy Survey
The Dark Energy Survey is a 5000 sq degree imaging survey of the South Galactic cap starting in 2011. It aims to make a photometric redshift galaxy map of the area that will be used in cluster counting, baryon acoustic oscillation, and weak lensing measurements of cosmology and dark energy, in conjunction with a supernova time domain survey. This talk will describe the DES, its status, and parts of the underlying cluster counting work.
The Stratospheric Observatory for Infrared Astronomy (SOFIA)
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a joint U.S./German Project to develop and operate a 2.5-meter infrared airborne telescope in a Boeing 747-SP that flies in the stratosphere at altitudes as high as 45,000 and is capable of observations from 0.3um to 1.6mm with an average transmission greater than 80 percent. SOFIA will be staged out of the NASA Dryden Flight Research Center aircraft operations facility at Palmdale, CA and the SOFIA Science Mission Operations Center (SSMOC) will be located at NASA Ames Research Center, Moffet Field, CA. First science flights will begin in 2009, the next instrument call and the first General Observer science call will be in 2010, and a full operations schedule of about 120 8 to 10 hour flights per year will begin in by 2014. The observatory is expected to operate for more than 20 years. SOFIA will initially fly with nine focal plane instruments that include broadband imagers, moderate resolution spectrographs that will resolve broad features due to dust and large molecules, and high resolution spectrometers capable of studying the kinematics of molecular and atomic gas lines at km/s resolution. We describe the SOFIA facility and outline the opportunities for observations by the general scientific community, future instrumentation developments, and operations collaborations. The operational characteristics of the SOFIA first-generation instruments are summarized and we give several specific examples of the types of scientific studies to which these instruments are expected to make fundamental scientific contributions.
The SZA, CARMA and the South Pole Telescope: New results and future plans
Transiting extra-solar planets: how do we find them and what can we learn from them
More than 300 extrasolar planets were discovered since 1995, when the first planet was detected.
About 50 of these planets eclipse their parent star once every orbital period. The detection of these transiting planets allowed in the last few years the derivation of the planetary dynamical masses and radii and sometimes even the planetary temperatures and atmospherical features. The transiting timing can be quite accurate, and therefore small deviations from the planetary Keplerian motion can also be detected. The talk will review the detection and study of the presently known transiting planets.