About Us

MSU-UM High Energy Interchange Talk Program

The Michigan State University - University of Michigan High Energy Interchange Talk Program is held on select Fridays. The talks switch between Michigan State and the University of Michigan. Lectures held at UofM are held at noon in the owl room (845 Dennison building).

Maps and directions to the department.

For more information contact Renato Dupke.

Members of the UM Department of Astronomy who wish tp schedule time to meet with the speaker from MSU should contact Jimmy Irwin.

Current And Upcoming Events
Date, Time and Location	Speaker	Abstract

Recent talks
Date, Time and Location	Speaker	Abstract
Fri, Mar 14 2008 12:00 pm Owl	Stephen, I Chun Shih MSU dept of Physics and Astronomy	The globular cluster black hole in NGC 4472 Maccarone et al. (2007) discovered the existence of an X-ray emitting black hole in a globular cluster in NGC 4472. This source is soft and luminous, alone with rapid variability in count rate by a factor of 7. In this talk, I'll discuss the nature of the source and the cause of the variability, which is most likely due to a partial obscuration by a precessing warped accretion disk.
Mon, Apr 21 2008 2:00 pm 1400 BPS	Monica Valluri U of M Astronomy	Evolution of phase space density in dark matter halos It has been known for many years that the phase space density profiles of dark matter particles obtained from cosmological N-body simulations are described by power-law profiles. I will present results of an analysis of the evolution of phase space density in DM halos and show how these power-law profiles arise naturally in hierarchical clustering scenarios. I will briefly discuss the implications of these results for our understanding of the properties of dark matter particles.
Fri, May 30 2008 12:00 pm Owl	Ming Sun MSU dept of Physics and Astronomy	Chandra studies of the X-ray gas properties of galaxy groups We present a systematic analysis of 40 nearby galaxy groups (kT_500=0.7-2.7 keV or M_500=10^13-10^14 h^-1 M_solar, 0.0120.15 r_500 and are consistent with a ``universal temperature profile\\\'\\\'. We present the K-T relations at six characteristics radii (30 kpc - r_500), for 40 groups from this work and 14 clusters from the Vikhlinin et al. (2008) sample. Despite large scatter in the entropy values at 30 kpc and 0.15 r_500, the intrinsic scatter from r_2500 is much smaller and remains the same (~11%) to r_500. The entropy excess at r_500 is confirmed, in both groups and clusters, but the magnitude is smaller than previous results. We also present scaling relations for the gas fraction. It appears that the average gas fraction between r_2500 and r_500 has no temperature dependence, ~0.12 for 1-10 keV systems. The group gas fractions within r_2500 are generally low and have large scatter. This scatter is shown to be tightly correlated with the scatter of the entropy at 0.15 r_500. This work shows that the difference of groups from hotter clusters stems from the difficulty of compressing group gas to inside r_2500. The large scatter of the group gas fraction within r_2500 causes large scatter in the group entropy around the center and may be responsible for the large scatter of the group luminosities. Nevertheless, the groups appear more regular and more like clusters beyond r_2500, from the results on gas fraction and entropy. Therefore, mass proxies can be extended into low mass systems. The M-T and M-Y relations derived in this work are indeed well behaved down to at least 2-3E13 h^-1 M_solar.
Wed, Nov 05 2008 3:00 pm Owl	Dr. Amalia Hicks MSU dept of Physics and Astronomy	Missing Baryons: Recent Results from X-ray Observations of High Redshift Clusters By virtue of their size, galaxy clusters can be used to place important constraints on cosmological parameters. In particular, charting the evolution of the cluster mass function provides us with vital information on the progression of large-scale structure formation over time. The masses of clusters, however, are often inferred from observables such as gas temperature or X-ray luminosity, which can be influenced by non-gravitational processes that affect cluster baryons, such as energy injection (heating) and radiative cooling. In addition, many high-redshift cluster surveys select samples based on baryon observables such as gas density. Recent correlations between temperature, luminosity, and total cluster mass indicate significant discrepancies between observations and the theoretical expectations of self-similarity. Therefore understanding changes in cluster properties with redshift is of crucial importance to surveys that intend to use the evolution of the cluster population as a proxy for cosmic evolution, and ultimately for the determination of cosmological parameters. Here I present the final results of an X-ray investigation of 13 high-redshift (0.6 < z < 1.1) optically-selected clusters from the Red-sequence Cluster Survey (RCS). Using a comparison sample consisting of moderate redshift (0.1 < z < 0.6) X-ray selected clusters, we find clear discrepancies in the normalizations of all scaling relationships involving baryon density (e.g., L-T). These results suggest that basic gravitational collapse is not the only process that regulates baryon heating in the potential wells of clusters, and that the central entropy of these high-z objects has been elevated by processes such as pre-heating, mergers, and episodic AGN outbursts. Perhaps most importantly, the core ratio of gas mass to total gravitating mass is systematically lower in our high-redshift sample, presenting a possible challenge to cluster surveys that rely (implicitly or explicitly) on the assumption of constant gas mass fraction to detect clusters and/or determine their masses.

-->See a list of Past talks.