Dept. of Astronomy Colloquia Schedule for Spring 2006
University of Texas at Austin

January 17

Robert Benjamin
  U of Wisconsin-Whitewater
GLIMPSE: Recent Results on Galactic Structure from the Spitzer Space Telescope
I present Spitzer/GLIMPSE (Galactic Legacy Infrared Midplane Survey Extraordinaire) results on the
global variation of the mid-infrared stellar and diffuse emission over 220 square degrees of the inner
Galactic plane from 10<|l|<65 degrees and |b|<1 degree using IRAC. Principle results include the
following: (1) variation of source counts indicate the Galaxy has a radial scale length of H_*=3.9 +/- 0.6 kpc;
(2) there is stron evidence for a Galactic bar with half-length R_bar=4.4 +/- 0.6 kpc, tilted by phi=44 +/- 10
degrees; (3) a major spiral arm of the Galaxy appears to be missing, (4) source counts are depressed even at
4.5 microns by extinction associated with molecular gas; (5) diffuse emission in all four bands is dominated
by star formation regions; and (6) there is a significant range in diffuse band rations: [4.5]/[3.6] varies by a
factor of ~10 along the Galactic plane, while [8.0]/[5.8] (the most tightly correlated bands) only varies by a
factor of ~2.

January 24

Michael Muno
Dead Stars Do Tell Tales: Chandra Observations of Dense Stellar Systems
With its sub-arcsecond resolution, the Chandra X-ray Observatory is for the first time revealing
large populations of white dwarfs, neutron stars, and black holes located in dense stellar systems. In
this talk, I will present Chandra observations of the central 100 pc of the Galaxy, and the massive
(10^5 Msun), young (4 Myr) Galactic star cluster Westerlund 1. I will describe how we are determing the
natures of the X-ray sources using a combination of comparisons to local Galactic X-ray sources,
theoretical population synthesis models, and searches for multi-wavelength counterparts. I will also
describe two surprising results. First, we have discovered that X-ray binaries are highly concentrated in
the central parsec of the Galaxy, and we suggest that they were formed through three-body interactions
between stellar binaries and a population of stellar-mass black holes that has settled into the deep
gravitational potential of the supermassive black hole Sgr A*. Second, we have discovered a slow X-ray
pulsar in the star cluster Westerlund 1, and established the progenitor to this neutron star was
surprisingly large, with an initial mass of at least 40 Msun. These results have inspired various theoretical
speculations that I will discuss throughout the talk.

January 31

Juntai Shen, Harlan J. Smith Fellow
  University of Texas at Austin
Dynamical Studies of Two Common Features in Disk Galaxies: Warps and Bars
The first part of my talk will be on the formation of galactic warps through an idealized form of
cosmic infall onto a disk galaxy. We can obtain warps that closely resemble those observed, and their
line of nodes generally forms a loosely-wound leading spiral in agreement with Brigg's rules. I will focus
on the mechanism of the warp formation and show that the leading spiral arises from the torques from the
misaligned inner disc and its associated inner oblate halo. Warps formed this way are not strongly damped
by the halo, therefore can persist for a few Gyrs, by which time another infall event can be expected.

I will also discuss a systematic study of the effects of central mass concentrations (CMCs) on bars with
N-body simulations. We find that bars are more robust than previously thought; the central mass has to be
as large as several percent of the disk mass to completely destroy the bar on a short timescale. For a
given mass, dense objects cause the greatest reduction in bar aplitude, while significantly more diffuse
objects have a lesser effect. Our findings show that neither typical supermassive black holes in spirals
nor typical central molecular gas concentrations should weaken the bar significantly within a Hubble time.
If time permits, I may also discuss some on-going work on making double-barred galaxies in N-body simulations,
and show that these interesting features may actually be pulsating.

February 7

Mariangela Bernardi
  University of Pennsylvania
Clues to the Formation of the Most Massive Galaxies in the Universe
I will report on two complementary samples of the most massive galaxies in the Universe. One
sample has the largest reported velocity dispersions in the Sloan Digital Sky Survey. The objects in
this sample potentially harbor the most massive black holes in the Universe. The other is a sample of
what are traditionally thought to be the most massive galaxies: brightest cluster galaxies. These are,
in fact, rather different types of objects. The objects with the largest velocity dispersions tend to
have smaller than expected sizes---they are the densest early-type galaxies. In contrast, the BCGs tend
to have larger than expected sizes. Both these samples appear to be slightly more homogeneous than the
bulk of the early-type galaxy population. I will discuss the implications for models of how these objects

February 9

Scott Chapman
  California Institute of Technology
Galaxy Evolution, Near and Far
Understanding galaxy evolution means moving beyond simply categorizing high redshift galaxy
populations at various wavelengths. I highlight detailed astrophysical information we are obtaining
from studies of the z~2.5 submillimeter-selected galaxies (SMGs), placing them in an evolutionary
context, discussing their duty cycle, and including the delayed buildup of their supermassive black
holes. I will also address how detailed 'archeology' of Local Group massive galaxies like Andromeda
and the Milky Way can provide complementary diagnostics of the formative processes of galaxies.

February 14

Emanuele Daddi
  National Optical Astronomy Observatory
The Old and the Unborn: Early Type Galaxies at High-z
The formation and assembly of massive early type galaxies is a central problem for galaxy evolution.
Recently we have shown that massive galaxies are common in the field all the way to redshift at least
2-3. They come in two main flavors: red and old galaxies and vigorous dust-reddened starbursts, both
of which are thought to be progenitors of local massive spheroids. While old/passive galaxies provide
constraints on the earliest episodes of star-formation and on the mechanisms needed to terminate it,
massive high-z starbursts allow us to directly probe the assembly and stellar formation processes.
I will present recent results from our ongoing efforts to characterize the properties and nature of
sources, using Spitzer and other facilities, and will discuss how they relate to some of the current
predictions of galaxy formation theories.

February 21

Eric Ford
  University of California at Berkeley
Planet Formation and Extrasolar Planets: What have we learned? What lies ahead?
For centuries, our knowledge of planetary systems and ideas about planet formation were based on a
single example, our solar system. During the last thirteen years, the discovery of over 150 planetary
systems has ushered in a new era for astronomy. I will review the observed properties of extrasolar
planetary systems and discuss how the surprising diversity of extrasolar planetary systems is
revolutionizing theories of planet formation. Despite rapid observational progress, many fundamental
questions remain to challenge astronomers and excite the public for many years to come. I will conclude
with a discussion of observational techniques that will eventually allow astronomers to address questions
that humans have pondered for millennia.

February 23

Milos Milosavljevic
  California Institute of Technology
The Future of Massive Black Hole Studies
I will present a vision of the future of the research into the cosmic origin of massive black holes.
We have grown accustomed to finding black holes at the centers of most galaxies in the observable universe.
The epoch and circumstances of their formation remain unknown. The gravitational binding energy in
black holes exceeds that in virialized baryonic structures, which suggests a profound influence of
black holes on galaxy formation. Our understanding of the formation of small galaxies, which are the
building blocks of structure in the universe, is severely incomplete, in spite of the recent successes
in the modeling of groups and clusters of galaxies.

Here I focus on several developing directions of inquiry. I discuss the interactions of multiple black
holes sharing the same galaxy as predicted by hierarchical structure formation, the dynamical interactions
of massive black holes, the conditions for black hole coalescence, and the implications of coalescence
(or lack thereof!) for massive black hole populations and for precision cosmological measurements. I argue
that the research into the origin of massive black holes will shift to petite objects in small galaxies,
paralleling a similar trend in galaxy surveys.

February 28

James Muzerolle  Steward Observatory
Probing the Initial Conditions of Planet Formation in Inner Protoplanetary Disks
The study of primordial disks around young low-mass stars is essential for our understanding of both star
and planet formation. A natural outcome of the initial collapse of molecular cloud cores, disks may be
the primary conduit for stellar accretion while also providing a suitable reservoir of dust and gas from
which planetary systems can form. I will review recent observations and modeling of the inner 0.1-10 AU
of protoplanetary disks, focusing on three key aspects: (1) accretion and the star-disk interface, where
measurements of mass accretion rates help to trace the evolution of the gas content of disks; (2) the structure
of the planet formation region of disks as revealed by infrared excess emission from dust, in particular
highlighting recent results from the Spitzer Space Telescope; (3) the timescales and mechanisms of primordial
disk dissipation and their connection to planet formation processes such as grain growth, planetesimal
coagulation, and core accretion. I will discuss future follow-up observations that will build on these recent
advances and further elucidate how common may be solar systems like our own.

March 2

Jenny Greene
  Harvard University
The Synchronized Growth of Black Holes and Galaxies
While black holes are apparently a ubiquitous component of the nuclei of local spheroids, their role in
galaxy evolution remains largely unknown. Due to the observed tight correlations between black hole
mass and both the galaxy bulge luminosity and stellar velocity dispersion, it is now possible to infer
black hole masses for active systems. Although these masses suffer significant outstanding uncertainties
(and potential biases), we are now in a position to track the evolution of black hole mass density in a
model-independent way. We may further begin to associate black holes of particular masses and growth rates
with the gas fractions, stellar populations and structures of their host galaxies, to test whether bulges
are indeed growing with their nuclei. I will focus specifically on the surprising result that even bulgeless
galaxies may host supermassive black holes. Although the structures of these galaxies indicate a very different
formation scenario than classical bulges, they nevertheless obey the same scaling relations between black hole
mass and stellar velocity dispersion observed in spheroids. These small galaxies host the least massive
supermassive black holes known, and thus provide one of the only observational constraints on the initial
mass distribution of black holes.

April 4

Ewine F. van Dishoeck
  Leiden Observatory
Chemistry in Evolving Protoplanetary Disks
Most pre-main sequence stars are surrounded by disks with sizes and masses comparable to those of
our own primitive solar system. While much attention has been paid to the analysis of continuum data,
line observations can provide important complementary information on the physical structure and chemical
composition of disks. High-J lines of CO and other simple gas-phase molecules (including deuterated species)
have been obtained with submillimeter telescopes to constrain the temperatures and densities, as well as
the chemical abundances. The presence of ices in the cold outer layers is suggested by recent Spitzer,
ESO-VLT and Keck mid-infrared spectra, whereas surprisingly large amounts of hot gas rich in organic
molecules are found in the inner disk of at least one object. The results will be discussed in the context
of models of flared and non-flared disks and their evolution from protostellar regions to the debris
disk phase. The importance of new observational facilities, in particular ALMA, Herschel and JWST, will
be emphasized.

April 18

Joel E. Tohline
  Louisiana State University
Population Boundaries for Galactic White Dwarf Binaries
in LISA's Color-Magnitude Diagram
When LISA (NASA's planned Laser Interferometer Space Antenna) is fully operational, astronomers will
have an unprecedented opportunity to study the properties of thousands, if not millions, of double white
dwarf (DWD) binary systems throughout our Galaxy. We will show how the gravitational-wave strain-frequency
diagram, which is usually used by physicists to illustrate LISA's expected capabilities, can be used as a
"color-magnitude" diagram for studying the population distribution as well as the evolution of DWD binaries.
Our present theoretical understanding of how DWD binaries evolve as they lose angular momentum through
gravitational radiation can be used to map out distinct population boundaries in LISA's "color-magnitude"
diagram. LISA should find that DWD binaries that are presently in a phase of stable mass-transfer populate
a region of this diagram that overlaps, but is much more confined than the region that is populated by
detached, inspiraling systems. LISA should also be able to identify DWD systems that are progenitors
of Type Ia supernovae.

April 25

Gary Hill and Phillip MacQueen
  University of Texas at Austin
Status Report on HETDEX
We will provide a brief update on the status of the HETDEX project, presenting definition and modeling
of the survey, technical progress on the HET Wide Field Upgrade and VIRUS, and a discussion of cost and
fundraising. We encourage a discussion following the presentation of parallel scientific projects that
will be enabled by the huge HETDEX dataset.

May 2

John T. McGraw
  University of New Mexico
The Quest for Precision Ground-Based Astronomy:
The CCD/Transit Instrument with Innovative Instrumentation (CTI-II)
Precision ground-based photometric and astrometric measurements enable new astrophysical research
programs. The CCD/Transit Instrument with Innovative Instrumentation (CTI-II) is the second generation of
a 1.8-m stationary, meridian pointing telescope fundamentally capable of millimagnitude photometry and
milliarcsecond astrometry. The optical design for this telescope is complete, and an innovative focal
plane mosaic including real-time focus feedback is being finalized. We discuss the telescope system
design considerations, support instrumentation and calibration techniques that allow this precision,
even for measurements made through Earth's turbulent and turbid atmosphere. Ancillary instrumentation Y includes optical and structural metrology and monitoring instruments, an atmospheric extinction li and a system of cameras capable of providing real-time extinction measurement
The CTI-II data, approximately 200 Gbytes nightly, will enable a large number of astrophysical research
programs including Galactic astronomy based upon motions and parallaxes of stars in the solar neighborhood,
discovery and synoptic monitoring of variability in the cores of galaxies, and the discovery of targets of
opportunity based upon either luminosity variability (e.g. supernovae) or motion (e.g. asteroids).

May 5

Naoki Itoh
  Sophia University

Seeing Galaxy Clusters Through Cosmic Microwave Background:
Sunyaev-Zeldovich Effect
Sunyaev and Zeldovich predicted in 1972 that microwave background photons coming from the direction
of galaxy clusters will show spectral distortion due to the Compton scattering by high-temperature electrons
that exist in the galaxy cluster plasma. This phenomenon has been observed by Gull and Northover in 1976.
Recent Sunyaev-Zeldovich effect observations with the use of interferometric telescope arrays by University
of Chicago group led by John Carlstrom have revolutionizedthe field. By this method detailed Sunyaev-Zeldovich
effect maps of about 60 galaxyclusters have been obtained by University of Chicago group. Many forthcoming
Sunyaev-Zeldovich survey observation projects of galaxy clusters will reveal thousands of galaxy clusters
and will shed light on the evolution of the universe. On the theoretical side, accurate relativistic
corrections to the Sunyaev-Zeldovich effect have been calculated by our group as well as some other groups,
thus enabling the precision theoretical treatment. These relativistic corrections are essential for the
forthcoming high-frequency observations of galaxy clusters.

Last Modified: August 2006