List of Past Astronomy Colloquia : 01-Sep-2004 to 31-Dec-2004

Date:   Wednesday 22-Sept-2004
Speaker:   Dr. Graeme Lufkin (University of Maryland)
Title:  Simulating Planet Migration in Gas Disks

Extrasolar planets have been surprising astronomers since their discovery. The biggest question: How did big planets get so close to their parent stars? The currently popular idea is planet migration via interaction with the circumstellar disk. I will cover what we know about extrasolar planetary systems, and introduce the theory of migration via disk-planet interaction. I will discuss and present results from simulations of this scenario, concluding with implications of the differences between theory and simulation.

Date:   Wednesday 29-Sept-2004
Speaker:   Dr. Tomasz Plewa (Univ. of Chicago)
Title:  Type Ia Supernova Explosion: Gravitationally Confined Detonation

Date:   Wednesday 06-Oct-2004
Speaker:   Dr. Carolyn Porco (SSI)
Title:  Splendor in the Rings: What Cassini Found When It Finally Got to Saturn

Date:   Wednesday 13-Oct-2004
Speaker:   No colloquium

Date:   Wednesday 20-Oct-2004
Speaker:   Prof. Doug Hamilton (University of Maryland)
Title:  The Tidal Evolution of Jupiter's Satellites

Date:   Wednesday 27-Oct-2004
Speaker:   Prof. Suzanne Staggs (Princeton)
Title:  Measuring Cosmic Microwave Background Polarization with the CAPMAP Experiment

Overwhelming evidence indicates that our complicated present-day universe (full of galaxies and stars and planets and at least some lifeforms) is evolving from a simple beginning as a dense cloud of hot plasma. The leftover, cooled-off radiation from the primordial plasma still permeates the universe, and is called the Cosmic Microwave Background (CMB). Inflation, reionization, and dark-matter-driven oscillations of the primordial plasma polarize the CMB slightly. The DASI experiment detected small polarization anisotropies in the CMB in 2002. I will report on new polarization measurements from the high-resolution CAPMAP, a 16-element correlation polarimeter array operating at 90 GHz, the sweet spot in the foreground spectrum.

Date:   Wednesday 10-Nov-2004
Speaker:   Prof. Tim Heckman (Johns Hopkins)
Title:  Spectra of 200,000 galaxies: implications for cosmic gastro-physics

We now have a very successful and tightly constrained model for the cosmic evolution of the structure of dark matter. The challenge is now to understand the ``gastrophysics'' by which the luminous baryons in the universe are painted onto the dominant dark matter component. This requires understanding the gas/star/black-hole ecosystem. The on-going Sloan Digital Sky Survey (SDSS) affords us the opportunity to examine the fossil record of galaxy and black hole evolution with unparalleled precision. I will summarize recent work based on optical spectra of over 200,000 SDSS galaxies. I will describe the methodology we have developed to measure the basic properties of these galaxies and of the active nuclei (accreting black holes) present in many of them. We find that galaxies exhibit a remarkably simple bimodal behavior in their ages and structure as a function of their mass. We also find that the most powerful active nuclei inhabit those rare galaxies that are both relatively massive and young. We perform a census of black hole growth using these AGN and find that the population of low mass black holes (M < 30 million M_sun) is growing rapidly today (mass-doubling time ~ a Hubble time), while the population of the most massive black holes is hardly growing at all today. We also find that the volume-averaged ratio of star formation to black hole accretion in bulge-dominated galaxies is ~1000, in remarkable agreement with the observed ratio of stellar mass to to black hole mass in nearby galaxy bulges. We conclude that bulge formation and black hole formation are tightly coupled even in present-day galaxies, but at lower characteristic mass-scales than in the past.

Date:   Wednesday 17-Nov-2004
Speaker:   Dr. Barry McKernan (University of Maryland)
Title:  The search for the hot missing matter

Date:   Wednesday 24-Nov-2004
Speaker:   none

Date:   Wednesday 01-Dec-2004
Speaker:   Prof. Christopher Reynolds (Univ. of Maryland)
Title:  X-ray Observations of Relativistic Gravity and Black Hole Spin

Date:   Wednesday 08-Dec-2004
Speaker:   Dr. Andrew Baker (Univ. of Maryland)
Title:  Millimeter Observations of High-Redshift Galaxies

Star-forming galaxies at z > 2.5 can be identified in the rest ultraviolet by the colors of their stellar continua, or in the rest far-infrared by the strength of their dust emission. The orthogonality of these selection techniques means that the "Lyman break" and "submillimeter" galaxy populations they identify are largely disjoint. Millimeter-wavelength observations are essential for constructing a unified picture of the two populations' key physical parameters. I will present sensitive measurements of continuum and molecular line emission from both Lyman break and submillimeter galaxies, and use these to test several predictions of galaxy evolution models.

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