KICP Seminars & Colloquia
KICP Seminars & Colloquia, Fall 2007
FRIDAY NOON SEMINARS
The Least Luminous Galaxies in the Universe - A Nearby Window to Cosmology
Beth Willman, Harvard-Smithsonian Center for Astrophysics
Since 2005, nearly 20 dwarf galaxies have been discovered around the Milky Way and M31 that are 100 times less luminous than any galaxy previously known. These discoveries are changing our understanding of galaxy formation at the lowest luminosities, and are also currently our most direct tracers of the properties of dark matter on small scales. I will present the properties of these new discoveries as a population, such as the spectroscopic observations that appear to confirm their residence within dark matter halos and the imaging that will ultimately reveal their star formation histories. I will also examine the properties of the Willman 1 object in detail to critically assess whether we can functionally distinguish globular clusters from dwarf galaxies at the extremely low luminosities at which future surveys may reveal an abundance of objects. I will discuss the implications of all these results in a cosmological plus galaxy formation context, including resolutions to the 'substructure problem' and predictions for the possible gamma-ray fluxes from annihilating dark matter particles in these tiny galaxies.
High-redshift Galaxy Groups and Clusters in DEEP2 and Beyond
Brian F. Gerke, KIPAC, Stanford Linear Accelerator Center
Groups and clusters of galaxies, as the largest, most recently formed objects in the universe, carry a great deal of information about the recent history of the cosmos. By studying these systems at a variety of epochs, it is possible to place strong constraints on theories of galaxy formation and on cosmological parameters. With the recent completion of the DEEP2 Galaxy Redshift Survey at z~1, we can now perform detailed studies of galaxy groups and clusters over a wider redshift range than ever before. In this talk I will present evidence that DEEP2 galaxy groups had only recently become suitable environments for shutting off star formation in galaxies. In addition, I will show results suggesting that DEEP2 groups are underluminous in the X-ray band, compared to local systems. I will also discuss an ongoing effort to constrain cosmological parameters by comparing the abundance of groups in DEEP2 to the abundance in the local universe. In particular, I will describe the primary challenges to performing this test reliably, and I will present a realistic plan for overcoming them. Finally, I will briefly mention some important implications of the DEEP2 results for future attempts to constrain cosmology with optical cluster surveys.
Population III stars and the formation of the first protogalaxies
Brian W O'Shea, Los Alamos National Lab
I use the cosmological adaptive mesh refinement code Enzo to do a suite of high-resolution numerical simulations of Population III protostellar clouds in a cosmological context. These calculations examine the formation of primordial protostellar clouds at a range of redshifts and in differing cosmic "neighborhoods." I find that these cores have a wide variety of accretion rates - varying by over two orders of magnitude - which may have significant implications for the IMF of Population III stars. I then simulate supernovae from the inferred stellar mass range and follow the evolution of the ensuing supernova remnant until the deposition of metal-enriched gas in the next generation of halos, which generally occurs ~50 million years after the original supernova. The dense gas in the core of these "child" halos is typically enriched to metallicities of ~10^-3 solar, which is above the "critical metallicity" at which metal line cooling dominates over molecular cooling, and suggests that the stars in these halos will have a significantly lower mass range than their Population III parents. This metal enrichment is a local phenomenon, and the transition of the universe from primordial to metal-enriched gas will be quite extended.
Constraining early universe relics with radio astronomy
Katherine J Mack, Princeton University
I will discuss recent work on using future radio astronomy observations to constrain populations of early universe relics. In the first half, I will present a method for constraining the existence of cosmic strings with gravitational lensing surveys. Past radio surveys have already ruled out a portion of the cosmic string parameter space, and future radio telescope arrays such as LOFAR and SKA have the potential to outperform current constraints from pulsar timing and the CMB by up to two orders of magnitude. In the second half, I will discuss the effect of evaporating primordial black holes on the ionization history of the universe, with an emphasis on the limits derivable from future 21-cm observations of high-redshift neutral hydrogen. In addition to giving us insight into the history of structure formation in the universe, 21cm surveys will also allow us to search for exotic physics in the Dark Ages.
OPEN GROUP SEMINARS
ASTRONOMY SPECIAL SEMINARS