List of Past Astronomy Colloquia : 01-Jan-2008 to 01-Jun-2008

Date:   Wednesday 30-January-2008
Speaker:   Dr. Eric Peng (STScI)
Title:  "Globular Clusters and Galaxy Evolution in the ACS Virgo Cluster Survey"

Globular clusters (GCs) are among the oldest known stellar populations, and their ubiquity across a wide range of galaxy luminosity and morphology points to a nearly universal early epoch of star formation. I will present new results from the most comprehensive survey of extragalactic globular cluster systems to date: The ACS Virgo Cluster Survey (ACSVCS). The ACSVCS is a Large HST/ACS program that has imaged 100 early-type galaxies in the Virgo Cluster, from giants to dwarfs, and has produced a catalog of ~11,000 GCs. I will discuss the metallicities and formation efficiencies of these GCs, how they relate to their hosts and environment, and implications for the hierarchical formation of galaxies.

Date:   Wednesday 6-February-2008
Speaker:   Dr. Nicole Vogt (New Mexico State University)
Title:  "Nine Billion Years of Galaxy Evolution: Disentangling Recent Evolution and Selection Biases in Disk Galaxies"

We review the status of current observations of the fundamental parameters of intermediate redshift (z < 1.3) disk galaxies. Modern instrumentation enables detailed measurements of galaxy luminosity, morphology, kinematics and mass, in both optical and the infrared passbands. By studying well known star formation indicators, the internal velocity structure and star formation rates of galaxies can be traced through this entire redshift regime. The combination of throughput and optimum seeing conditions yields spectra which can be combined with high resolution multiband imaging to explore the evolution of galaxies of various morphologies, and to place constraints on current models of galaxy formation and star formation histories.

Out to redshifts of unity, these data form a high redshift Tully-Fisher relation that spans four magnitudes and extends to well below L*, with no obvious change in shape or slope with respect to the local relation. A comparison of disk surface brightness between local and high redshift samples yields an offset in accordance with distance-dependent surface brightness selection effects, as can the apparent change in disk size with redshift for disks of a given mass. The effects of imaging and spectral selection are shown to be significant, dependent not only upon the broad-band luminosity and surface brightness of targets but also a strong function of emission line strength and spectral flux distributions. These results provide further evidence for modest increases in luminosity with lookback time for the bulk of the observed field spiral galaxy population.

Date:   Tuesday 12-February-2008
Speaker:   Dr. Jeremiah Ostriker (Princeton University)
Title:  "Concordance Cosmology: Is It Correct?"

Beginning early in the 20th century with the discovery that the spiral nebulae were giant systems like our own Galaxy and the Hubble/Slipher finding that the velocity difference between pairs of galaxies increased roughly linearly with their separations, the stage was set for our modern cosmological models framed as solutions to Einstein's equations for perturbations growing gravitationally in an approximately uniform and isotropic cosmos.

The startling discovery, which was very slow to be accepted, that most of the gravitating matter in the universe is "dark" and of (still) unknown composition and the still more puzzling but now widely accepted conclusion that gravity on the largest scales is overwhelmed by a repulsive force associated with "dark energy" completes the well established, if somewhat bizarre, standard model. Within this framework, very small amplitude, approximately scale-invariant, adiabatic perturbations were imposed by still unknown processes. All current large scale cosmological observations are consistent with this picture, and the detailed computer simulations based on the model appear to fit with steadily increasing precision both the detailed knowledge that we have of the local universe and the increasingly accurate evolutionary picture that we can construct by studying our own past light cone with large ground and space based telescopes that effectively use the universe as a time machine. Hoping to fill the substantial gaps in our understanding, major experiments are underway which should better constrain the unknown parameters and perhaps can test more sharply the present dominant paradigm.

Date:   Wednesday 13-February-2008
Speaker:   Dr. Remy Indebetouw (University of Virginia)
Title:  "Star Formation and Feedback in the Nearby Universe: Insights from Spitzer"

I will discuss some of the lessons we are learning from Spitzer observations of the Magellanic Clouds and our Galaxy. (Relatively) high resolution mid-infrared imaging provides an unbiased view of star formation in diverse environments from the inner to outer Galaxy and into the Magellanic Clouds and even in the Bridge. In the LMC, the SAGE survey recently presented here by Margaret Meixner is allowing detailed investigation of star formation scaling relations such as the Schmitt-Kennicutt law, on scales less than 100pc. Building on such photometric results, spectroscopy reveals detailed physical conditions in circum(proto)stellar gas and dust. We can study the feedback effects of the 30 Doradus super star cluster on sub-parsec scales, and start to make detailed comparisons of star forming regions in those different environments.

Date:   Tuesday 19-February-2008
Speaker:   Martin White (University of California - Berkeley)
Title:  "The Echo of Einstein's Greatest Blunder"

The coupling of baryons and photons by Thomson scattering in the early universe leads to a rich structure in the power spectra of the cosmic microwave background photons and the matter. The study of the former has revolutionized cosmology and allowed precise measurement of a host of important cosmological parameters. The study of the latter is still in its infancy, but holds the potential to constrain the nature of the dark energy believed to be causing the accelerated expansion of the universe. I will discuss how we can measure this cosmic sound, and the theoretical developments that need to be made before we can realize the promise of future experiments.

Date:   Wednesday 20-February-2008
Speaker:   Dr. Michael E. Brown (Caltech)
Title:  "The Dwarf Planets of the Outer Solar System"

The past few years have seen an explosion in the discoveries of Pluto- and near Pluto-sized bodies in the outer solar system, giving rise to a new classification of "dwarf planets." Like Pluto, each of these largest dwarf planets has a unique story to tell about the history and evolution of the solar system. I'll discuss the discoveries of these objects and the new views of giant collisions, stellar encounters, and planetary rearrangement that we are gaining from their study.

Date:   Wednesday 27-February-2008
Speaker:   Dr. Ethan T. Vishniac (McMaster University)
Title:  "Disk Dynamos and the Origin of Magnetic Fields in Galaxies"

One of the more challenging problems in cosmology is understanding the origin of galactic magnetic fields. Proposed seed mechanisms give large scale magnetic fields which are typically about 14 orders of magnitude weaker than currently observed. Moreover, observations at high redshift give no indication of systematically weaker galactic fields. This has led to a large number of proposals involving novel physics at very high temperatures and very early epochs in the universe. Here I will discuss progress in understanding large and small scale dynamo effects in highly conducting fluids. This leads to the prediction that galaxies will reach equipartition between disk turbulence and disordered magnetic fields within a few hundred million years. The long wavelength tail of these fields will be about 1.5 orders of magnitude below current values and should reach them within another few hundred million years.

Date:   Wednesday 05-March-2008
Speaker:   Dr. Dale P. Cruikshank (NASA/Ames Research Center)
Title:  "Organic Matter on Solar System Bodies: From Colors to Spectral Bands"

The red colors of many small bodies of low albedo in the outer Solar System (planetary satellites, asteroids, Centaurs, comet nuclei, and Kuiper Belt objects) have long been thought to arise from complex organic matter on their surfaces. Proof of this conjecture has been lacking because no specific spectral absorption bands pointing to particular organic materials could be found. The Cassini mission to the Saturn system has afforded the opportunity to study the near-infrared spectra of several of the planet's satellites in greater detail and in spectral regions unavailable from Earth-based observatories. Spectral bands of organic materials are now seen in the low-albedo materials of several of Saturn's satellites, notably the "dark side" of Iapetus. We can now pursue the next levels of detail to get greater insight into the actual organic chemicals present, their origins, and their relationship to organics in meteorites, comet dust, and interplanetary dust particles. This inquiry leads us to the inevitable questions of the role of organic chemicals in space in the origin of life on at least one planet.

Date:   Wednesday 12-March-2008
Speaker:   Dr. Markos Georganopoulos (UMBC)
Title:  "The Diffuse Infrared Background: A New Way to Probe It"

The diffuse infrared background is a very interesting and notoriously hard to directly measure astrophysical quantity. I will review the physical importance of it, the methods that have been used, so far, for constraining it, and I will present an idea for a new, independent method to probe it.

Date:   Wednesday 19-March-2008

Date:   Wednesday 26-March-2008
Speaker:   Dr. Paul Martini (Ohio State University)
Title:  "The Evolution of AGN in Clusters of Galaxies"

Galaxies in clusters have undergone profoundly different evolution relative to their counterparts in the field. I will present new results that show the same holds true for the supermassive black holes at the centers of cluster galaxies. Comparision of low-redshift and high-redshift clusters shows that luminous AGN are substantially more common in high-redshift clusters, and that the population increases more rapidly than the field AGN population over the same redshift range. This substantial difference in the AGN evolution between the field and clusters is indicative of an environmental dependence to AGN downsizing. As AGN feedback appears to lead to substantial heating of the intracluster medium, the evolution of the AGN population may have important implications for the use of the intracluster medium as a cosmological tool.

Date:   Wednesday 02-April-2008
Speaker:   Dr. John Wallin (George Mason University)
Title:  "Probing Gravity in the Outer Solar System"

The detection of flat rotation curves in galaxies and the "missing mass" in clusters of galaxies have left astronomers with two main possibilites - either the universe is filled with particles that have yet to be directly detected or the standard theory of gravity fails at large scales. Although there is growing observational evidence for dark matter, there are very few tests of gravity on scales > 10 AU. One such test comes from the analysis of the Pioneer 10 and 11 spacecrafts' tracking data. Both of these spacecraft show an unmodeled deceleration of approximately 8.7 x 10^{-10} m/s^2 beginning about 10 AUs from the Sun. If this anomoly cannot be explained by spacecraft systematics, it will represent a serious challenge to our standard theory of gravity. To test the veracity of the "Pioneer Anomoly" as a gravitational perturbation, we have analyzed the astrometric data of m inor planets in the outer solar system for evidence of orbital perturbations.. In this talk, we will discuss the results of this analysis, along with the challenges of using planets and minor planet tracking data to probe gravity. We will also discuss how future surveys such as the LSST can place tight limits on any deviation from classical theories of gravity at distances between 20 AU and 100 AU from the Sun.

Date:   Wednesday 09-April-2008
Speaker:   Dr. Frank Shu (University of California-San Diego)
Title:  "Star Formation: Disks, Jets, and Outflows"

Date:   Wednesday 16-April-2008
Speaker:   Dr. Pieter van Dokkum (Yale University)
Title:  "The Turbulent Past of Massive Galaxies, and the End of 'Monolithic Collapse'"

A long-standing prediction of galaxy formation models in a cold dark matter-dominated Universe is that massive galaxies were assembled through mergers of smaller galaxies. However, there has been little direct evidence for this idea. In fact, the homogeneity and old stars of elliptical galaxies have been used as arguments for an alternative model, that of galaxy formation in a single "monolithic" collapse at early times. I will discuss two recent observational results which demonstrate that massive galaxies do indeed have a very turbulent past, and were not yet fully assembled when the Universe was ~3 billion years old.

Date:   Wednesday 23-April-2008
Speaker:   Dr. Kelly Holley-Bockelmann (Vanderbilt University)
Title:  "Growing Supermassive Black Holes: An N-body Mechanic's Perspective"

Astronomers now know that supermassive black holes are a natural part of nearly every galaxy, but how these black holes form, grow, and interact within the galactic center is still a mystery. I will discuss how we can use N-body simulations to track the interplay between galaxies, dark matter halos, and supermassive black holes. We have discovered that the shape of the galaxy influences the black hole, but the effect is not entirely one-sided. Supermassive black holes leave an imprint on the galaxy structure as well, and surprisingly, can even change the structure and kinematics of the intracluster medium where galaxies live. There is more work to be done to uncover how supermassive black holes and galaxies co-exist, and I will talk about what important questions remain.

Date:   Thursday 24-April-2008
Speaker:   Dr. Janet Luhmann (UC-Berkeley)
Title:   "The STEREO Mission's Quest to Understand Space Weather - and Space Weather So Far"

Date:   Wednesday 30-April-2008
Speaker:   Dr. Daniela Calzetti (University of Massachusetts)
Title:  "Measures of Star Formation"

I review extant methods for estimating star formation rates across the electromagnetic spectrum, comparing extragalactic with Galactic (Milky Way) estimators. Present (GALEX, Spitzer) and future (Herschel, JWST) space facilities have opened new windows or increased sensitivity in old ones for measuring star formation rates in both local and distant galaxies. This important parameter not only is key to the investigation of galaxy evolution, but provides insights into the physics of star formation in galaxies. For the latter, the upcoming Large Millimeter Telescope will set the stage for the exploration of the new frontier. I finally review the outlook from the point of view of recently approved Herschel Key Projects.

Date:   Wednesday 07-May-2008
Speaker:   Dr. Debra Meloy Elmegreen (Vassar College)
Title:  "Clumpy Galaxies in the Early Universe"

Observations of galaxies out to z~5 in the Hubble Ultra Deep Field reveal unusual clumpy morphologies in addition to spirals and ellipticals. These high redshift galaxies are mostly starburst systems, with star-forming regions 1000 times more massive than in today's galaxies. Many of the clumpy galaxies have thick disks that are half the size of local galaxies and lack bulges and exponential disks; they may grow through merging and accretion, and evolve into today's spirals when the star-forming clumps migrate to the centers or dissolve. Transitions are seen at z~1, when the universe was half its present age.

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