Colloquium Schedule for SPRING 2008
|
Colloquium Schedule for SPRING 2008 |
|
3:45-Refreshments in LGRT 1033 Lounge; 4:00-Talk in LGRT 1033 Lecture Area MAY 1: Abstract: Black holes form in the early Universe and grow to billions of solar masses as their gravity attracts surrounding matter. This cosmic accretion releases a huge amount of energy, which is expected to have a strong influence on galaxy formation. The history of black hole growth can be traced through the detection of Active Galactic Nuclei out to very high redshifts; however, most AGN have been discovered in optical and ultraviolet surveys, which are strongly biased against obscured accretion. We describe the evidence, from deep multiwavelength surveys using Spitzer, Hubble, Chandra and the largest ground-based telescopes, that most AGN are heavily obscured, and that obscuration decreases with increasing luminosity and increases with redshift. A simple extrapolation from the local unification paradigm explains the shape and intensity of the integrated X-ray background, as well as the redshift and flux distributions of AGN at infrared through X-ray wavelengths. We also describe recent results from deep gamma-ray surveys that constrain the properties of the most heavily obscured AGN, and prospects for mapping the history of cosmic accretion through future surveys. MAY 8: ************************************************************************************************************************************ JANUARY 31: FEBRUARY 7: Abstract: I will present results from two major programs that we are undertaking to investigate the spatially resolved gas kinematics in redshift 2-3 star forming galaxies. We are using millimeter interferometery from the IRAM Plateau de Bure telescope to measure the CO kinematics and gas masses in ~20 highly obscured, ultra-luminous submillimeter galaxies. We are also using the adaptive-optics assisted integral field spectrometer, SINFONI, on the ESO-VLT to study the distribution of star formation and kinematics from redshifted H-alpha emission in about 70 high-redshift galaxies, the SINS project. Many of these systems show clear evidence for possessing large, thick, unstable rotating disks. In contrast, the submillimeter galaxies are clearly undergoing major merger episodes. I will compare and contrast the results from the different galaxy populations and to show how these results are providing new understanding of galaxy evolution in the early Universe. FEBRUARY 14: Abstract: The first stars and galaxies lie at one of the most compelling frontiers of 21st century astrophysics. Beginning in the next decade, JWST and its contemporaries will seek out these objects in the high redshift Universe. I will show how the rapidly growing field of "Galactic Archeology" can yield discoveries about the first stars and galaxies that powerfully complement direct observation at high redshift with data on kinematics and chemical abundances in the oldest components of the Milky Way. Using a new theoretical model for the hierarchical formation and stochastic chemical evolution of the Galaxy, I will show how newly discovered chemical abundance signatures constrain the mass function (IMF) of the first stars and their immediate descendants during the epoch of reionization. Since this theoretical model has been constructed to explicitly incorporate data from the low- and high-redshift Universe, the derived IMFs can be tested directly with JWST and its contemporaries in space and on the ground. With much more Galactic Archeology data coming in the five years leading up to JWST, we can look forward to a rich and detailed picture of the epoch of first light brought into sharp focus by this new synthesis of data. FEBRUARY 21: Abstract: I will review our recent work on galactic diffuse hot gas as a tracer of stellar feedback and its relationship to the formation and evolution of galaxies, concentrating on ones that show no ongoing starburst or AGN. I will first summarize relevant observations, including the X-ray/far-UV absorption line spectroscopy of hot gas in our Galaxy and the X-ray imaging of nearby galaxies to highlight various clues that these observations offer to the understanding of the feedback. I will then present our hydrodynamic simulations of hot gas structure and evolution, including the feedback from galactic stellar bulges. These simulations show that the feedback can play an essential role in shaping the galactic gaseous structure and evolution and may provide a solution to several long-standing problems in understanding various galaxies, including the so-called missing stellar feedback and over-cooling problems. FEBRUARY 28: Abstract: I will discuss young Solar-type stars at the Classical T Tauri stage when the star is surrounded by a disk of gas and dust and in many cases winds and jets are observed. These stars have strong magnetic fields which govern the matter flow around the star and determine most of their observational properties. I will show results of our 3D and 2D simulations of disk accretion onto young magnetized stars which show that the disk accretion may be in stable or unstable regimes with different observational properties. Modeling of outflows from the disk-magnetosphere boundary shows two-component outflows: most of the matter outflows in conical relatively slow winds, while a smaller amount of matter outflows to very fast axial jets. I will compare models with observations and will discuss successes and puzzles in understanding young stars. MARCH 6: MARCH 13: Abstract: The question of how local conditions may affect the star and cluster formation processes has implications for our understanding of how stars formed in the early universe. The young star clusters in the Small Magellanic Cloud (SMC) are ideal benchmarks for this research, given their sub-solar metallicity and 1/5 solar dust content. The close proximity of the SMC allows us to perform a detailed and accurate census of its stellar population. Using deep ACS/HST observations, we have fully characterized the stellar content in a number of young star clusters in the SMC, located in different regions of this galaxy such as the ¡Èbar¡É and the Magellanic ¡Èbridge¡É, to study the effect of "different" environments on the way stars and clusters form. We find that the youngest clusters host rich populations of low mass pre-Main Sequence stars, indicating that star formation is recent and, possibly, still ongoing. We present our findings on mass function, upper mass cutoff and mass segregation and discuss their implications for our understanding of cluster formation and evolution. MARCH 20: MARCH 27: Abstract: With deep, large-area multi-wavelength surveys providing thousands of galaxies at z>2, primary galaxy statistics such as luminosity function, and clustering measures have been constrained with better precision in recent years. In this talk, I will present the newly improved correlation function measures for the faintest galaxies at z~4 known to date from the GOODS survey, which clearly show the transition of correlation function from halo-halo clustering to sub-halo clustering, as well as the well-known luminosity-dependent clustering amplitude. Using these measures, I will show that by combining a simple scaling law between their observed UV luminosity and halo/subhalo masses and halo mass function, one can set a limit to the star formation duty cycle of these faint star-forming galaxies. Such a limit is a key to understanding the nature of the most populous class of objects observed at high redshifts, and thus shed light on what was the major mode of their early mass assembly, namely continuous star-formation via steady gas accretion or collisional starbursts. APRIL 3: Abstract: The nature of dark matter is one of the outstanding questions of astrophysics. The internal motions of member stars reveal that the lowest luminosity galaxies in the Local Group are the most dark-matter dominated. New large datasets allow one to go further, and determine systematic properties of their dark-matter haloes. In addition, the chemical abundances of the stars constrain star formation, gas flows and `feedback'. APRIL 10: Abstract: Understanding asymptotic giant branch (AGB) envelope ejection and planetary nebula (PN) evolution is essential in astrophysics, since low- and intermediate-mass stars and their ejecta are excellent probes of stellar populations in galaxies, and have been detected in all types of galaxies and in the intra-cluster space. Stars in this mass range constitute a major component (by mass) of the stellar material in the Universe, and thus a correct understanding of their evolution in different environments has the potential to advance many astrophysical fields. Furthermore, these stars play a fundamental role in cosmic recycling, being major contributors to the carbon and nitrogen abundances for the next generation of stars. In this talk I will show the latest results on Magellanic Cloud PNe, including data acquired with HST and Spitzer. Magellanic Cloud PNe are important both because their distances are well known -- while this is not true for Galactic PNe -- and because they extend the metallicity baseline for AGB and PN studies. APRIL 15 (Tuesday): Abstract: Panchromatic deep surveys have grown ever larger over the last decade, providing tremendous observational resources for tracing the growth and evolution of galaxies at high redshift. Deep Spitzer surveys, in particular, are offering new insight into star formation, the growth of stellar mass, and energetics from active nuclei, and have been particularly powerful when carried out in conjunction with Chandra, HST, and ground-based surveys over the same sky areas. I will review recent progress measuring and understanding galaxy growth throughout most of cosmic history, based on observations from many programs, including the GOODS and FIDEL Spitzer Legacy surveys, and with an eye toward the (near) future and the Herschel Observatory. APRIL 24: Abstract: We have analyzed the redshift-dependent fraction of galactic bars over 0.2 |