Spring 2004 Astronomy Colloquia - University of Texas at Austin

February 3, 2004
Benjamin McCall
University of California at Berkeley
"The Chemistry of H3+ in the Diffuse Interstellar Medium"
H3+, the simplest polyatomic molecule, plays a key role in dense interstellar clouds as the initiator of ion-molecule
chemistry. Thedetection of H3+ in diffuse interstellar clouds came as a surprise, however, and suggested a serious
(factor of ~100) problem in thesimple model of diffuse cloud chemistry. In particular, this observation raised questions as
to the applicability of laboratory measurements of the H3+ dissociative recombination rate to interstellar conditions. We
have recently measured the dissociativerecombination rate of rotationally cold H3+ ions in an ion storage ring, and have also
detected H3+ in the classicaldiffuse cloud towards _ Persei, where the electron fraction is known from previous observations.
This combination of new laboratory measurements and astronomical observations has eliminated two of the primary uncertainties
in the chemical model,and implies a previously unrecognized and significant enhancement in the cosmic-ray ionization rate in
the diffuse interstellar medium

February 4, 2004
Joop Schaye  
Institute for Advanced Studies, Princeton
"The Chemical Enrichment of the Intergalactic Medium"

February 5, 2004
Paul Goldsmith  
Cornell University

"Inappropriate Probes of Dense Molecular Clouds"
In this talk I discuss some unexpected results obtained using the world's smallest and largest radio
telescopes. They deserve the above appellation because they involve the surprising absence of O2 ,
a key expected molecular species, and the unanticipated presence of a large abundance of an
atomic species, HI, in "molecular" regions. The first part of the talk concerns molecular oxygen (O2),
studied with the Submillimeter Wave Astronomy Satellite (SWAS), which has been in operation since
December 1998. We have not detected this species at a level of a few times 10-7 relative to H2. This is
several orders of magnitude below the prediction of steady-state gas phase chemistry, and suggests
that significant other factors must be at work, possibly turbulent diffusion or depletion of gas-phase
oxygen onto grain surfaces, or both. A tentative detection of O2 in the Rho Oph A molecular outflow
suggests that conditions there may reset the chemical clock, and briefly allow abundances expected
from standard chemical models to prevail. The second portion of the talk concerns recent Arecibo
observations of HI in cold quiescent clouds. This atomic gas is manifest by very narrow absorption
features, referred to as HI Narrow Line Self-Absorption, or HINSA. When the absorption profiles are
analyzed, and HINSAand molecular maps compared, it is evident that there is considerable atomic
hydrogen at temperatures between 10 and 20 K, well-mixed with the molecular material. In some
clouds, the fractional abundance of HI is consistent with theoretical models based on cosmic
ray destruction of H2, but in others there is a factor up to 100 excess atomic gas, again suggesting
that other processes are at work which significantly change the composition of "molecular" clouds,
make atomic H the third most abundant constituent after H2, and He, and which we need to appreciate
in order to understand how low mass star formation operates in these regions.

February 10, 2004
Rob Hynes
University of Texas at Austin
"A Multiwavelength View of Galactic Black Holes"
Galactic black holes accreting from binary companions provide our best opportunity to study stellar mass black holes and
accretion processesonto them. They are powerful emitters across the electromagnetic spectrum and coordinated
multiwavelength studies provide a powerfultool to probe accretion astrophysics in this environment. I will describe some of
the outstanding problems in the field, illustrateexamples where combining information from different energy bands
advances our understanding, and indicate opportunities that will be enabled by the next-generation of X-ray and optical

February 12, 2004
Marc Kuchner  
Princeton University
"Reading the Resonant Signatures of Planets in Debris Disks"
A planet in a circumstellar dust cloud can carve an easily visible signature in the dust density via orbital resonances. This
pattern can point to the planet and reveal its orbit even when the planet itself is much too faint to see. I will paint an overview
of the variety of resonant structures a single planet on a moderately eccentric orbit can create in an optically thin dust disk

and compare the resonant geometries found in the solar zodiacalcloud with observations of debris disks around Vega,
Epsilon Eridani, and other stars.

February 13, 2004
Marc Kuchner  
Princeton University
"A Coronagraph with a Band-limited Mask for Finding Terrestrial Planets"
The last few years have seen many clever new ideas for telescopes to image
extrasolar planetary systems. But all you need to get is a classical coronagraph--
with a "Band-Limited Mask". I'll describe this optical trick, which offers unlimited dynamic
range and high throughput to planet seekers who can provide a flat wavefront, and discuss
some advantages and disadvantages of the technique compared to other Terrestrial Planet Finder

February 17, 2004
Andrew Baker  
Max-Planck-Institut für Extraterrestrische Physik
"Galaxy Formation at High Redshift: A Millimeter View "
Star-forming galaxies at high redshift 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 samples 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 at z > 2.5, and
demonstrate how these can be used to test the predictions of galaxy evolution models regarding star formation rate, star
formation mode, and assembly of baryonic mass.

February 19, 2004
Shardha Jogee  
Space Telescope Science Institute
"Evolution of Disk Galaxies: Internal and External Triggers"
Non-axisymmetric features such as stellar bars, general triaxialities such as those of galactic halos, and external triggers

(interactions and mergers) redistribute angular momentum and mass in disk galaxies, driving their dynamics, central
activities, and structural evolution. I will discuss aspects of this evolution over a wide range of cosmic lookback times by
presenting panchromatic studies of nearby systems as well as recent work on disks at redshifts z=0.5-1 based on the
largest HST surveys to date, GEMS (Galaxy Evolution from Morphology and SEDS) and GOODS (Great Observatories Origins

Deep Survey). I will outline how bar-driven gas inflow can build within the inner kpc a molecular environment which differs
remarkably from that of the outer disk. I will discuss the implications for the dynamics, onset of starbursts, and secular
evolution in the inner kpc. I will discuss fueling mechanisms for central AGN and starbursts. Finally, I will present ongoing
work on issues where our knowledge is still in its infancy. While most present-day disk galaxies are barred, how did
bars form, evolve, and impact disk structure (e.g., pseudo-bulges,bulges) over the last 10 Gyr? What is the role of tidal

interactions and mergers in this evolution?

February 23, 2004
Volker Bromm  
Harvard Center for Astrophysics
"The First Sources of Light"
How and when did the cosmic dark ages end? I present simulations of the formation of the first stars and quasars, discuss

their feedback on the IGM, and describe ways to probe their signature with WMAP and JWST. The first supernovae are
responsible for the initial metal enrichment of the IGM, and I address the impact of this initial enrichment event on the
subsequent history of structure formation. Finally, I describe the properties and statistics of high redshift GRBs and SNe
that result from the first generation of stars.

February 24, 2004
Dale Frail  
National Radio Astronomy Observatory
"Diversity in Cosmic Explosions"
High energy transients, once defined solely by their gamma-ray burst emission, are now recognized as exhibiting a

remarkable diversity in their properties such as duration, peak spectral energies, and the relativve partitioning of
energy in relativistic and non-relativistic components. I will review the observational progress in this field while noting where
substantial gaps in our understanding remain.

February 26, 2004
Elizabeth Barton  

Steward Observatory, Univ. of Arizona
"The Role of Starbursts in the Evolution of Galaxies"
The origins of the Hubble sequence, and thus the origins of galactic bulges, are key to unraveling the evolutionary histories of

galaxies in the universe. While massive, R^1/4-law bulges probably form from merger processes at high redshift, a relatively
new class of "exponential" or "pseudo-bulges" are consistent with more recent formation from disk-related processes such
as secular evolution, minor mergers, and close galaxy-galaxy passes. The luminous compact blue galaxies already observed
at intermediate redshift may be these bulges in formation. I will describe ongoing observational efforts to explore this
possibility and, more generally, to measure the incidence of central starbursts and in situ bulge formation both locally and at
intermediate redshift. I will also briefly discuss a search for the earliest known star-forming galaxies, at redshifts z > 7,
arguing that they may be detectable with present-day technology.

March 2, 2004
Sandy Faber  
University of California, Lick Observatory
"Recent Results from the DEEP Survey of the Distant Universe"
New telescopes and instrumentation are bringing the distant universe within scrutiny as never before. The speaker has led the

construction of a major new spectrograph at the Keck Telescope, DEIMOS, which is being used to conduct a large survey of
65,000 galaxies at redshifts z~1. This talk will briefly describe the spectrograph
and summarize recent scientific results of

the survey.

March 4, 2004
Gabriela Mallen-Ornelas  
Harvard Center for Astrophysics
"The EXPLORE Project: A Deep Search for Transiting Extrasolar Planets"
Planet transit searches promise to be the next big step forward in short-period extrasolar planet detection and

characterization. Each transiting planet discovered will have a measured radius, and follow-up radial velocity observations will
lead to an absolute mass measurement for transiting planets. A radius measurement is essential for determining a planet's
bulk composition and evolutionary history. The EXPLORE Project started in 2001 as a series of transit searches using
wide-fieldCCD mosaic cameras on 4m-class telescopes. We simultaneously monitor tens of thousands of stars with high

photometric precision (0.002-0.01 mag) and 3-minute time sampling, and use the resulting light curves to search for the tell-
tale flat-bottomed eclipses caused by transiting planets. We have a pipeline to completely reduce the data in less than a
month, which allows same-semester radial-velocity follow-up. I will describe the strategy and design considerations of the
EXPLORE Project, and show planet candidates for which radial velocity observations have been carried out.

March 5, 2004
Gabriela Mallen-Ornelas  

Harvard Center for Astrophysics
"Metallicities and Internal Kinematics of Intermediate Redshift Galaxies
Associated with Damped Lyman Alpha and MgII Absorption Systems

Damped Lyman Alpha systems (DLAs) at intermediate and high redshift are widely believed to represent the progenitors of

present day galaxies, and studies of DLA abundances have been used to trace the chemical enrichment history of the
Universe. However, the precise nature of these systems and the interpretation of their absorption line profiles and
metallicities is still contentious. One of the big questions in the study of DLAs is that it is not clear whether these absorption
systemsare caused by large disk galaxies, or by infalling clumps. Another big question in absorption line systems
studies is that there is very little evolution in the weighted metallicity of DLAs between 0.5 < z < 3,
and it has been suggested

that the supposedly random sightlines of background QSOs do not trace the mainmetal reservoirs in galaxies. I will present
early results of a project to study the comparison between the metallicities and internal kinematics of galaxies associated
with DLA and Mg II absorption systems, and the metallicities and internal kinematics of the absorbing gas seen in the QSO

March 9, 2004

Meg Urry  
Yale University
"The Demographics of Supermassive Black Holes"
Active Galactic Nuclei (AGN) are signposts for actively accreting supermassive black holes. AGN are common in the
early Universe(z~2-3) but may be undercounted by factors of 3-10 because obscuration by gas and dust prevents their
inclusion in UV-excessor optical surveys. With the unprecedented combination of the Spitzer (infrared) Space Telescope,
the Chandra X-ray Observatory,and the Hubble Space Telescope, there is now a unique opportunity to find obscured AGN
at the epoch of peak black hole accretion andpeak star formation. The Great Observatories Origins Deep Survey (GOODS)
project, conceived nearly 4 years ago as the deepest multiwavelength probe to date, was designed to find obscured AGN at
z~2-3. I willpresent first results on AGN from the GOODS survey, including evidence for a substantial population of obscured
AGN. We reconcile the apparent disagreement with the redshift distribution in the deep Chandra surveys, and make predictions
for the far-infrared counts, which willbe tested by the Spitzer GOODS observations being done in early 2004.

March 23, 2004

Anneila Sargent  
California Institute of Technology
"GOOD CARMA - Millimeter-wave Interferometer Observations of Star
and Planet Formation"

In astronomy, unexpected discoveries and insights often result when new instruments become operational, when new wavelengths

become accessible to observation, or whennew measuring techniques are introduced. Over the last few decades, millimeter wave
interferometers have enabled a wide range of detailed observational studies of the various phases of the stellar birth and early evolution,
particularly in molecular clouds whereobscuring dust prevents optical measurements. Our understanding of the way stars form and evolve
has improved dramatically. Nevertheless, more powerful instruments that are capable of reaching higher resolution, highersensitivity, and even
shorter wavelengthsare required. CARMA - Combined Array for Research in Millimeter-wave Astronomy -is one such instrument. CARMA will merge
Caltech’s Owens Valley Radio Observatory (OVRO) array and the Berkeley-Illinois-Maryland(BIMA) Association’s array at a newhigher elevation site
in the Inyo Mountains near the current OVRO. Results from recent arrayresearch on star and planet formation will be presented to demonstrate
both the
achievements and limitations of the current instrumentsand expectations for CARMAwill be described.

March 30, 2004
Peter Mészáros  
Penn State University
"Gamma-ray Bursts: High Energy Perspectives and Low Energy Surprises "
After a brief review of the phenomenology of gamma-ray burst sources, I discuss the fireball shock scenario and some recent

developmentssuch as the supernova connection, polarization, X-ray flashes, etc. Current problems and issues are touched upon,
and I then describe the prospects for high redshift observations, GeV-TeV photon andneutrinos, cosmic-rays and gravitational wave

April 6, 2004
Lynne Hillenbrand  
California Institute of Technology
"Young Stars, Star Clusters, and Proto-planetary Disks"
The quest to understand the formation of stars and planetary systems similar to our own is a fundamental goal of modern astrophysics.
Star formation studies make use of observational techniques at all wavelengths ranging from x-ray ==> radio. This talk will review
progress over the past several years derived largely from optical and near-infrared imaging and spectroscopic data on topics such
as the diversity in star-forming environments, bulk cluster quantities such as the stellar (and now sub-stellar) initial mass function
and the history of star formation,and finally on the survival times of protoplanetary disks and the prospects for planet detection.

April 13, 2004
Ralf Bender
Max-Planck-Institut fuer Extraterrestrische Physik
"Evolution of Galaxy Luminosity Functions from z=0 to z=5 "
Galaxy luminosity functions present one of the simplest tests of galaxy formation models. I will discuss the evolution of blue band galaxy
luminosity functions as derived from the VLT FORS Deep Field. The VLT FDF reaches almost the depth of the Hubble Deep Fields but covers a
factor 8 larger area than one of the HDFs. Accurate photometric redshifts enable the determination of L*, phi* and alpha. Coherent evolution
of M* and phi* is found for rest wavelengths of 1500A to 5000A, alpha* does not seem to evolve significantly. I briefly compare our results with
predictions by semi-analytic galaxy formation models.

April 20, 2004
Sacha Kopp
Department of Physics, University of Texas at Austin
"Testing Quantum Oscillations of Lepton Flavor Using an Accelerator Neutrino Beam"
The weak interaction, so far as we know, conserves lepton flavor quantum number. Consequently neutrinos, which participate only in the weak
interaction, are created or annihilated purely in a state of some neutrino flavor. What happens to a freely propagating neutrino in between its time
of creation and annihilation, however, is undetermined. I will review evidence of cosmic ray experiments which suggest that freely-propagating
neutrinos exhibit oscilllations between one neutrino flavor type and another, as is allowed in quantum mechanics. I will further discuss an
effort based at the Fermi National Accelerator Laboratory to confirm this evidence using a controlled accelerator beam of neutrinos launched
through the Earth, to emerge in northern Minnesota, where our detector is located. The detector is already completed, and the beamline facility is
under construction, due to turn on in December of this year.

May 5, 2004
Neal Evans
University of Texas at Austin
"The AT-25 Project: The Case for UT Involvement"
The AT-25 project is a joint project of Cornell and Caltech to build a 25-m class telescope at a high sight in Chile. The telescope will work
from millimeter wavelengths to 200 microns. This project forms an essential complement to our efforts in the optical/NIR. I will discuss
the background,
the telescope, interest among the Texas community, and the prospects for joining this project.

Back to Colloquia Webpage Page last modified 08/9/04