List of Past CTC Theory Lunches : 01-Sep-2008 to 31-Dec-2008

Date:   Monday 15-Sep-2008
Speaker:   Javier Ballesteros-Paredes (UNAM, Morelia)
Title:   Six Myths on the Virial Theorem for Interstellar Clouds

Date:   Thursday 25-Sep-2008
Speaker:   Thomas Statler (Ohio University)
Title:  The Hot Interstellar Medium in Normal Elliptical Galaxies

This talk will describe a comprehensive analysis of the morphology and thermal structure of the hot, X-ray emitting gas in normal elliptical galaxies, using data from Chandra X-ray Observatory. Morphologically, X-ray gas has little in common with the shape of the stellar distribution. The gas often appears disturbed, and exact hydrostatic equilibrium is the exception rather than the rule. The gas is sufficiently far out of equilibrium that it retains no information about the shape of the gravitational potential. We quantify the asymmetry, and find it to be strongly correlated with AGN activity. This AGN-morphology connection persists all the way down to the weakest AGN luminosities, arguing for the general importance of AGN feedback, even in normal galaxies. The temperature profiles in these systems are highly varied: we find positive gradients, negative gradients, quasi-isothermal, and hybrid profiles. The outer temperature gradient is uncorrelated with galaxy properties, but strongly influenced by the environment. The inner gradient is unaffected by the environment but strongly correlated with galaxy characteristics. Three scenarios may explain the inner gradients: (1) weak AGN heat the ISM locally, while higher-luminosity AGN heat the system globally; (2) negative gradients indicate a declining importance of AGN relative to other heat sources; or (3) the variety of temperature profiles are snapshots of different stages of a time-dependent flow.

Date:   Monday 04-Nov-2008
Speaker:   Andrey Kravtsov
Title:   Modeling molecular hydrogen and star formation in galaxy formation simulations

Date:   Monday 10-Nov-2008
Speaker:   Kris Beckwith
Title:  'Disks, Fields and Jets: The Role of Magnetic Field Geometry in Black Hole Accretion Flows'


'Because the magnetorotational instability is capable of exponentially amplifying weak pre-existing magnetic fields, it might be hoped that the character of the magnetic field in accretion disks would be independent of the nature of the seed field. However, the divergence-free nature of magnetic fields in highly conducting fluids ensures that their large-scale topology is preserved, no matter how greatly the field intensity is changed. By performing global two- and three-dimensional general relativistic magnetohydrodynamic disk simulations with several different topologies for the initial magnetic field, we explore the degree to which the character of the flows around black holes depends on the initial topology. We find that while the qualitative properties of the accretion flow are nearly independent of field topology, jet launching is very sensitive to it; a sense of vertical field consistent for at least an inner disk inflow time is essential to the support of strong jets.'

Date:   Monday 17-Nov-2008
Speaker:   Rachel Somerville
Title:  Bulge formation and AGN feeding in major mergers

It has been shown recently that incorporating the energy feedback from growing supermassive black holes into models of galaxy formation set within the Cold Dark Matter framework can plausibly solve several of the most persistent problems that plagued these models for decades, such as the 'overcooling' and 'star formation quenching' problems. I will discuss whether these models can rise to the challenge of correctly predicting the observed "downsizing" in stellar mass and star formation rate with cosmic time, as seen in lookback studies and in "fossil" evidence in nearby galaxies. I will then show how a revision of the classical model for spheroid formation via galaxy mergers leads to improved predictions for the fraction of early type galaxies as a function of stellar mass. Finally, I will discuss whether these "unified" models can simultaneously reproduce the evolution of galaxies and AGN over cosmic history, and what general lessons we can take away from the successes and failures of the models.

Date:   Monday 24-Nov-2008
Speaker:   Chris Reynolds
Title:   What's the trouble with radio-mode feedback?

Date:   Monday 1-Dec-2008
Speaker:   Soebur Razzaque (NRL)
Title:  Are Gamma-ray bursts the sources of ultrahigh energy cosmic rays?

Gamma-ray bursts (GRB), being the most powerful explosions in the universe, have long been considered as candidate sources of ultrahigh energy (>EeV) cosmic rays. However, a confirmation is still elusive and requires correlated observation by GeV-TeV gamma-ray telescopes such as Fermi, VERITAS, MAGIC, HESS; and by neutrino telescopes such as IceCube. I present results from theoretical investigations of the expected gamma-ray and neutrino signatures of cosmic-ray acceleration in GRB in light of recent results from the Auger and HiRes cosmic-ray detectors.

Date:   Monday 8-Dec-2008
Speaker:   Mia Bovill
Title:   Winter School on Local Group Cosmology

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