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Past MSU-UM High Energy Interchange Talk Program
| Recent talks | ||
| Date, Time and Location | Speaker | Abstract |
| Wed, Jan 21 2009 12:00 pm 1400 BPS | Mark Reynolds U of M Astronomy | Title: X-ray Binary Systems The importance of X-ray binary systems (XRBs) is twofold. On the one- hand they allow us to investigate questions of purely astrophysical importance (e.g. stellar evolution, accretion physics), while at the same time providing testbeds for fundamental physics complementary to earth based experiments (i.e. ultra-dense matter, General Relativity tests). A large number of X-ray binaries have been detected in the Galaxy (> 300), consisting of both low-mass and high-mass systems containing black hole and neutron star primaries. Point sources of X-rays have also been detected in external galaxies, where the X-ray emission is dominated by XRBs, and have been found to exhibit similar characteristics, as a population, to those observed in the Milky Way. In this talk, I will present our efforts to measure the masses of the compact object in these systems. Further observations which aim to reveal the nature of the accretion flow in these X-ray binary systems will also be discussed. |
| 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. |
| 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, 0.012 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. |
| 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, 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. |
| Fri, Nov 30 2007 12:00 pm 1400 BPS | Brian Nord, Rebecca Stanek and Elena Rasia U of M Astronomy | Brian Nord TITLE: Effects of Selection and Covariance on Scaling Relations of X-ray Galaxy Clusters Rebecca Stanek: TITLE:The Effect of Baryonic Physics on the Halo Mass Function Elena Rasia TITLE: Testing scaling relation and their scatter with a bullet-like simulated cluster |
| Fri, Oct 19 2007 12:00 pm Owl | Mark Voit MSU dept of Physics and Astronomy | |
| Thu, Sep 20 2007 1:30 pm 1400 BPS | Jimmy Irwin U of M Astronomy | The Low Metallicity ISM of X-ray Faint Elliptical Galaxies Since the hot interstellar medium (ISM) of early-type galaxies is believed to originate primarily from stellar mass loss and supernovae, the metallicity of the ISM should reflect that of the stars contributing the mass to the ISM. This has been confirmed for gas-rich X-ray bright ellipticals, as both the X-ray-determined ISM abundances and optically-determined stellar abundances are approximately solar. However, this does not seem to be the case for gas-poor, X-ray faint ellipticals, for which very sub-solar abundances have been reported, although poor statistics and significant X-ray binary contamination have been listed as the cause of these (erroneously) low abundance measurements. We present Chandra + XMM-Newton spectra of one of the best-observed X-ray faint ellipticals, NGC4697, and confirm that O, Ne, Mg, Si, Fe, and Ni are all significantly subsolar, and are not the result of poor spectral fitting or poor statistics. We speculate that the low metal abundances are the result of dilution from the accretion over time of pristine metal-free gas that surrounds the galaxy. |
| Fri, Aug 17 2007 12:00 pm Owl | Ming Sun MSU dept of Physics and Astronomy | X-ray gas of galaxies in clusters: mini-cooling cores, AGN feedback, stripping and star formation I will discuss the population properties of X-ray thermal coronae of early-type galaxies in nearby hot clusters. Cool galactic coronae (kT= 0.5-1.1 keV) have been found to be common, > 60% in > 2 L* galaxies. Their survival from ICM stripping, evaporation, rapid cooling, and powerful AGN outflows provide rich information on gas stripping, microscopic transport and feedback processes in the cluster environment. Updates based on new Chandra data will also be presented. Late-type galaxies evolve significantly in clusters. I will discuss one example with rich phenomena in X-rays and Halpha, the starburst galaxy ESO 137-001 in the nearby massive cluster A3627. A 70 kpc narrow X-ray tail and a 40 kpc Halpha tail have been found, as well as at least 29 HII regions downstream of the galaxy. The high surface number density and luminosities of these HII regions dwarf the previously known examples of isolated HII regions in clusters. We suggest that stripping of the ISM not only contributes to the ICM, but also adds to the intracluster stellar light through subsequent star formation. |
| Fri, Jul 13 2007 2:00 pm 1400 BPS | Joel Bregman U of M Astronomy | The Missing Hot Baryons in the Local Universe |
| Fri, Jun 15 2007 12:00 pm Owl | Dr. Arunav Kundu MSU dept of Physics and Astronomy | Implications of the Low Mass X-Ray Binaries - Globular Cluster Link Low mass X-ray binaries (LMXBs) are among the most visible tracers of neutron stars and black holes. The Chandra and XMM telescopes have discovered large populations of LMXBs in nearby galaxies. Recent studies have showed remarkably, that half the LMXBs in these galaxies are associated with globular clusters. The specific characteristics of individual globular clusters, such as metallicity and age, and the wide range of globular cluster properties in these galaxies provide a unique window into the formation and evolutionary histories of LMXBs. I present results from our recent studies of the LMXB-globular cluster connection in nearby galaxies, including the discovery of a black hole X-ray binary in a globular cluster, and discuss the implications on LMXB, globular cluster, and galaxy formation and evolution. |
| Fri, May 11 2007 11:00 am 1400 BPS | Dr. Renato Dupke U of M Astronomy | Fossil groups are galaxy systems that present an unusual lack of bright galaxies in the inner regions, except for of a giant central E galaxy. Recent measurements of galaxy velocity dispersion in fossil groups are consistent with the dynamical state of the system as determined from X-ray observations. This indicates that they have relatively deep gravitational potential wells, more typical of clusters. The popular mechanism proposed to "wipe out" the big galaxies surrounding the central dominant galaxy is still cannibalism. If so, and if the galaxy population is heterogeneous, strong galactic winds resulting from galaxy merging might be trapped by their deep potential wells destroying the central enhancement of SN Ia/SN II ejecta ratio typically seen in other galaxy groups. This can be tested by looking at the distribution of metal abundance ratios near the core. I will discuss a few preliminary results based on this methodology with the Chandra satellite for the best (observationally) fossil groups. |
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