No talk scheduled.
|Rennan Barkana Caltech, and Tel Aviv University
Gravitational The earliest generations of galaxies are thought to have heated
and reionized the universe. The most promising way to study cosmic reionization
is to detect emission in the redshifted 21-cm line of atomic hydrogen. I will explore
the ability of measurements of the 21-cm power spectrum to enable the simultaneous
reconstruction of the reionization history and the properties of the ionizing sources.
I will show that our ignorance about the properties of the galaxies affects the accuracy
of the reconstruction, but the expected accuracy is still rather hight. I will also present
a detailed analysis of the 21-cm PDF (i.e., histogram of pixel values) and show that
it may offer an independent observational method for reconstructing the reionization
history. Finally, I will consider the early stages of hydrogen or helium reionization,
and show that even at quite high redshifts, a significant fraction of the ionized volume
resided in bubbles containing multiple sources.
Rachel Mandelbaum The Institute for Advanced Study, Princeton, NJ
|Gregory B. Taylor University of New Mexico
"The Evolution of Radio Galaxies from Parsec to Megaparsec Scales"
Depending on where (and when) you look in our Universe, radio emission from active
galaxies is either rare (~ 1 in 10 for field galaxies) or commonplace (almost 100% in
the centers of dense clusters of galaxies at low redshifts). I will disculss what triggers
the radio emission, how the growth of the radio source is influenced by its environment,
and how it in turn can have a profound effect on the host galaxy. It is becoming
well established that some form of feedback mechanism regulates the fuel supplied
to the central dominant AGN in galaxy clusters. Details of the accretion and the energy
transport are still to be understood and are important for the study of not just clusters
, but galaxy evolution as well. By studying the radio emission of the central dominant
AGN over a broad range of physical scales we can read the history of energy input
to the cluster. I will describe some of the radio observations from parsec to
mega-parsec scales. Low frequency observations are of particular interest to explore
these problems, and I will spend some time describing the Long Wavelength Array
|David S. P. Dearborn Lawrence Livermore National Laboratory (visit: 09/25-10/01)
"The Use of Nuclear Explosives to Disrupt or Divert Asteroids"
Nuclear explosives are a mature technology with well-characterized effects. Proposed
utilization for reducing the threat of an asteroid impact include a standoff burst to
ablate surface material and nudge the body to a safer orbit. This can be done without
risk of fragmentation when there are decades of warning, and the required speed
change is small (~1 cm/s). For shorter lead times, (a keyhole passage scenario like Apophis)
a direct sub-surface burst can fragment the body. With only 1000 days lead time,
shattering an NEO reduces the material impacting the Earth to about 1/100,000th
of the original body, a huge mitigation factor. To better understand these possibilities,
we have used a multidimensional radiation/hydrodynamics code to simulate sub-surface
and above surface bursts on an inhomogeneous, 1 km diameter body with an average
density of 2 g/cc. The body, or fragments (up to 750,000) are then tracked along
|Special Event: Antoinette DeVaucouleurs Medalist Prize-Winner in Astronomy (visit: Oct. 6-10)
Christopher F. McKee University of California/Berkeley
"Massive Star Formation: Theory and Observational Predictions"
Stars more than about 10 times the mass of the Sun are responsible for creating
most of the heavy elements in the universe, for governing the evolution of galaxies, and
most likely for reionizing the universe a few hundred million years after the Big Bang.
The formation of these stars can be understood as an extension of the theory of
low-mass star formation, but two major problems must be overcome: First, for massive
stars, the outward force due to radiation pressure exceeds the inward force due to gravity;
how can gas accrete onto the star in that case? Circumstellar disks, outflow cavities, and
radiative Rayleigh-Taylor instabilities all contribute to the solution of this problem.
Second, why does a gas cloud form a single massive star instead of fragmenting into
hundreds of low-mass stars? This problem can be solved by thermal feedback from
the first stars to form in the cloud. These conclusions are validated by the first 3D
radiation-hydrodynamic simulations of high-mass star formation. Observational
predictions include (1) Massive stars should form in cores with surface densities
of order 1 g cm^2; (2) the stellar initial mass function (IMF) should follow the mass
function of cores in the host molecular cloud, scaled down by a factor of a few;
(3) massive, turbulent disks detectable by ALMA and the EVLA should occur
around massive protostars; and (4) star formation in regions of low surface density
should have an IMF that is truncated at high mass, and as a result, the star
Donald E. Winget University of Texas at Austin
|Casey Papovich Texas A&M University
"Witnessing Galaxy Formation at High Redshifts"
The combination of NASA's Great Observatories provides a unique, panchromatic view of
distant galaxies. I will discuss how observations of cosmologically distant galaxies with
these facilities have improved our understanding of galaxy evolution. In particular, I will
discuss recent results from the Spitzer Space Telescope, which measures the infrared
emission from obscured star formation and AGN. I will focus on recent results from several
deep surveys to study the assembly of massive galaxies at high redshifts, which are based
on the properties of their infrared emission. I will also discuss a program to study gravitationally
lensed distant galaxies with Spitzer and other telescopes, which will provide a detailed view
of very distant star-forming galaxies. I will summarize the current constraints on the assembly
histories of distant galaxies, and discuss challenges that remain to understand galaxy evolution.
|R. Michael Rich University of California, Los Angeles
"The Galactic Bulge: New Surveys and New Results"
The central bulge of the galaxy is the nearest example of an old, metal rich, spheroid
population. I will report on detailed abundances of its stars, and results of a new radial
velocity survey. The bulge shows some fo the dynamical characteristics of a pseudobulge,
yet also has a vertical abundance gradient and is older than 10 Gyr. Chemical signatures
are consistent with formation of the bulge on a timescale of < 1Gyr. The abundance
gradient and rapid formation timescale pose challenges if the bulge's structure
|James P. Lloyd Cornell University
"Precision Radial Velocities in the Near Infrared with TEDI"
The TEDI (TripleSpec - Exoplanet Discovery Instrument) is a dedicated instrument
for precision near-infrared radial velocities combining the moderate resolution TripleSpec
spectrometer with an externally dispersed interferometer. With the goal of achieving meters
per second radial velocity precision, TEDI will enable searches for planetary companions
to the lowest mass stars. Heretofore, such planet searches have been limited almost entirely
to the optical band and to stars that are bright in this band. Consequently, knowledge about
planetary companions to the populous but visibly-faint low mass stars is limited. Current radial
velocity searches for planets around early M dwarfs with visible wavelength spectrometers
have already yielded remarkable discoveries. The extension of this capability to longer
wavelengths opens up new opportunities in numerous mid-late M dwarfs and brown dwarfs.
TEDI has been commissioned on the Palomar 200" telescope in December 2007, and is
currently in a science verification phase.
Nov. 11th -
Special Event: Conference on Galaxy Evolution: Emerging Insights and Future Challenges
(no colloquium scheduled on Nov. 11, to avoid conflict with this event.)
|Special Physics and Astronomy Colloquium: 4:15 P.M. RLM 4.102 (John Wheeler Lecture Hall)
Andrew Hamilton University of Colorado at Boulder
What really happens inside black holes? As first pointed out by Poisson & Israel (1990),
Special Event: Beatrice M. Tinsley Visiting Professor in Astronomy (visit: Nov. 3 - Dec. 4)
No talk scheduled.
Laurent Loinard Instituto de Astronomia - UNAM, Morelia, Mexico
"The Space Distribution of Nearby Star-formation"
Using the excellent astrometry capabilities of the Very Long
Baseline Array, we have measured
I will end my talk by mentioning preliminary results in
other regions (particularly Serpens and