|Fall 2005 Astronomy Colloquia - University of Texas at Austin|
September 6, 2005
Penn State University
"X-raying Active Galaxies in the High-Redshift Universe: Results from Snapshot
and Deep Surveys"
X-ray surveys of high-redshit (z ~ 2-6) active galaxies have advanced dramatically over the past few
years, largely due to complementary results from Chandra and XMM-Newton. These investigations probe
the accretion processes by which the most massive black holes grew as well as their larger scale nuclear
environments. I will review some of the recent X-ray results on high-redshift active galaxies, derived from
snapshot and deep surveys. Topics covered will include the cosmic evolution of active-galaxy X-ray
emission, constraints on radio-quiet quasar energetics and outflows, X-ray emission from radio-loud
quasars at pc-to-kpc scales, and the active-nucleus content of submillimeter-luminous galaxies. I will
describe how these studies are laying crucial observational groundwork for future missions including
Constellation-X and XEUS, and I will outline some future prospects.
September 13, 2005
University of Cambridge
"Hierarchical Build-up of Massive Black Holes"
I'll discuss a model for the hierarchical growth of supermassive black holes, feeding pregalactic
black hole seeds, end-product of the first generation of stars. Mergers and dynamical interactions,
as well as the consequences of gas accretion, will be critically addressed. I'll also discuss
the constraints on the early evolution of the black holes required by the observations of z=6 quasars.
September 19, 2005
"What Lies Beneath: Spitzer Infrared Spectography Observations
of Ultraluminous Infrared Galaxies"
September 20, 2005
University of Texas at Arlington
"Seismology of Stellar Atmospheres"
Atmospheres of late-type stars and some white dwarfs are heated by different forms of non-radiative
energy generated in convection zones of these stars. Recent studies show that this energy also excites
atmospheric oscillations, which can be used as indicators of stellar activity. In this talk, I shall
describe newly developed theoretical tools to predict periods and amplitudes of these oscillations in
different stars. I shall identify the best methods to observe the oscillations and show how to use them to
probe the structure of stellar atmospheres.
September 21, 2005
University of Colorado at Boulder
"Precision Cosmology with Galaxy Clusters: Weighing in with Simulations"
The role of galaxy clusters as probes for precision cosmology is critically analyzed using numerical
simulations with the adaptive mesh N-body/hydro code Enzo. We first examine the formation and evolution of
clusters within a LCDM cosmology including nongravitational effects. The simulations illustrate that clusters
have a complex history of accretion which accounts for recently observed cluster substructure, cool fronts,
filaments, and cool "bullets". We also propose a new model for the formation of cool core clusters via
hierarchical mergers. The nonequilibrium environment of clusters poses a challenge for accurate mass
determinations which, in turn, is important in constraining the dark energy equation of state. One promising
possibility from our simulations is a new dark scaling relation between the integrated Sunyaev-Zeldovich effect
y-parameter and cluster mass.
September 27, 2005
Carnegie Institution of Washington
"Giant Planet Formation: Theory vs. Observations"
October 11, 2005
Space Telescope Science Institute
"Star Formation in the Small Megellanic Cloud"
Studies of resolved stellar populations provide essential information to understand the evolution of galaxies.
I will present a comprehensive effort currently underway to study and understand the star formation history of
the Small Magellanic Cloud (SMC) and some results from the first set of HST/ACS observations of SMC young
clusters. These allowed us to discover a previously unknown rich population of low mass (down to 0.5 Mo)
pre-mainsequence stars. The implications of such discovery will be discussed.
October 18, 2005
University of British Columbia
"Baryon Oscillations as a Cosmological Ruler"
The universe contains a small excess of galaxy pairs separated by the special distance of 490 million light years.
This preferred scale was imprinted by sound waves in the early universe, 380,000 years after the Big Bang, when
baryons and photons were tightly coupled together. This year, large galaxy surveys have measured the existence of
the preferred scale in the local universe for the first time, confirming our fundamental theories for the formation
of cosmic structure. The phenomenon is known as "baryon oscillations".
In this talk I will explain how the preferred scale can be used as a cosmological "standard ruler" to map out
distances in the universe (in an analogous manner to the use of distant supernovae as "standard candles"). This will
enable us to distinguish between competing models for the "dark energy", the mysterious component which appears
to make up 70% of the current energy of the Universe, but whose nature is unknown.
I will discuss the fundamental theory of baryon oscillations, my simulations of future spectroscopic and photometric
galaxy redshift surveys, and outline the theoretical and observational challenges that have to be faced to realize
the potential of this new cosmological probe.
October 24, 2005
Astrophysical Institute Potsdam
"Galaxy Formation and the Formation of the Galaxy"
October 25, 2005
"A Gravitational Tractor for Moving Asteroids"
I will discuss a method of towing a threatening asteroid to prevent a collision using a spacecraft
which hovers near the asteroid. The big advantage of this method is that it is highly controllable,
and does not critically depend upon the structure, composition, or rotation of the asteroid. For the
particular case of asteroid 99942 Apophis, which has a close Earth approach in 2029 followed by a
possible return in 2036, I will show how this concept spacecraft can be used to deflect this asteroid.
November 1, 2005
University of Colorado
"The Emerging Role of Quasar Outflows in"
Cosmological Structure Formation"
Over the last few years the potential importance of quasar outflows on the growth of super-massive
black holes, enrichment of the intergalactic medium, evolution of the host galaxy, cluster cooling
flows and the luminosity function of quasars has been widely recognized. I will review these
theoretical developments and describe the efforts of our research group to determine observationally the
most relevant parameters for these models: Chemical abundances and kinetic lumionsity of
observed quasar outflows.
November 8, 2005
UC Observatories/Lick Observatory
"Extragalactic Globular Clusters and Galaxy Formation"
Globular clusters are excellent tracers of the major star forming episodes in a galaxy's history.
Studies of the sub-populations in extragalactic globular cluster systems are providing important
constraints on the dominant mechanisms and epochs of galaxy assembly. I will discuss current ideas on
globular cluster/galaxy formation, including their connection to dark matter halos in the early
universe and their potential to constrain the epoch and (in)homogeneity of reionization. Recent
results from the Hubble Space Telescope and the Keck 10-meter telescopes will be emphasized.
November 22, 2005
Los Alamos National Laboratory
"The Life and Death of the First Stars"
will represent an overview of the current understanding of the evolution and final fate of primordial
massive stars. I will start with a brief introduction on the evolution of massive stars in general. Then
I will discuss the peculiarities of the evolution of massive and very massive primordial stars. Depending
on their initial mass with increasing mass they can produce a neutron star, a black hole, no remnant at all
(though a gigantic explosion), or an intermediate mass black hole. Also the nucleosynthesis signature of these
stars varies and strongly depends on this initial mass and the final fate of these stars. The predicted
signatures will be discussed in the frame of currently available observational data.
December 6, 2005
"Physical Conditions of QSOs as Revealed from FeII Emission Spectra"
The enrichment of Fe, relative to alpha-elements such as O and Mg, represents a potential means to measure
the ages of QSOs and to probe nucleosynthesis in the galaxy formation epoch. QSOs exhibit prominent Fe II features
and Mg II 2800Å resonance doublet emission in the UV. Although the Fe/Mg ratio in chemical evolutional models are
expected to decrease with redshift, measurements of Fe II(UV)/Mg II emission ratios show a large scatter from 1 to 20,
with no redshift dependency up to z ~ 6.4. Before using Fe II emission as an abundance indicator, one must ascertain
how Fe II emission varies with physical conditions and abundance.
An 830-level model atom for Fe II used in photoionization calculations predicts that Fe II(UV)/Mg II ratios strongly
depend on the non-abundance factors, microturbulence, ionizing flux, and hydrogen density; all of which must be taken
into account before any accurate abundance can be derived. Calculations clearly demonstrate that Fe+ is the dominant
coolant at densities found in AGN Broad Line Regions, the Fe II emission strongly contributes to the continuum
and Mg II line. Thus, Fe II study can not be ignored in deriving Spectra Energy Distribution (SED) of the QSO in
the UV and measuring Fe II(UV)/Mg II ration. This is why, in spite of its complexity, analysis of the Fe II spectra
must be taken into account in photoionization modeling of AGN spectra.
Last Modified January 3, 2006