12-day Event Forecast

November 24, 2009 Tuesday 3:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

Aleks Diamond-Stanic
University of Arizona

The Growth of Supermassive Black Holes: A Biased View

The growth of supermassive black holes can be traced via the observed luminosities of active galactic nuclei, but for most sources the line of sight is blocked by gas and dust. Commonly used luminosity indicators (e.g., X-ray continuum, optical line emission) are often attenuated by several orders of magnitude, and it is difficult to accurately estimate extinction corrections. The [O IV] 26 micron line is more robust because it probes high-ionization gas and suffers little dust attenuation. Using Spitzer measurements of [O IV] for a complete sample of 90 local Seyfert galaxies, we find that the luminosity distributions of obscured and unobscured AGNs are indistinguishable, even though the obscured sources are systematically fainter in terms of [O III] optical and 2-10 keV X-ray emission. In addition, as part of of our work to calibrate the relationship between [O IV] and AGN intrinsic luminosity, we find that even hard (10-200 keV) X-rays are biased tracers, particularly for Compton-thick sources. This has important implications for the census of black hole growth from future X-ray surveys.

December 2, 2009 Wednesday 2:00 PM 
Meyer 5th Fl. CCPP Lounge
High Energy Physics Seminars (hep)

Shlomo Razamat
SUNY, Stony Brook

TBA

December 2, 2009 Wednesday 4:00 PM 
Meyer 6th Floor Conference Room
Soft Condensed Matter Seminars (csmr)

Hartmut Loewen
Heinrich-Heine-Universitat at Dusseldorf

Particle-resolved Instabilities in Colloidal Dispersions

Dispersions of colloidal particles are excellent model systems of classical statistical mechanics in order to understand the principles of self-organization processes. Using an external field (e.g. electric or magnetic field) the effective interaction between the colloidal particles can be tailored and the system can be brought into non-equilibrium in a controlled way. In this talk, we shall discuss lane and band formation in oppositely driven colloidal mixtures, both in DC and AC driving fields. The experimental realization in colloids and dusty plasmas is highlighted.

December 3, 2009 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)

James Carpenter

TBA

December 4, 2009 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

David Law
UCLA

Tidal Disruption in a Triaxial Milky Way Dark Matter Halo: A Revised Model for the Sgr dSph Galaxy

Observations of the lengthy stellar streams produced by the tidal destruction of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) can provide strong constraints on the distribution of mass within the Milky Way. However, previous work has yielded conflicting results: while the angular precession of the streams has been thought to indicate an oblate shape for the Galactic halo, the radial velocities of stars in these streams are only reproduced in prolate halo models. I demonstrate that both observational characteristics are naturally reproduced by orbits within a triaxial Milky Way dark matter halo similar to that expected from current CDM theory. I conclude by summarizing the properties of the revised Milky Way --- Sgr system and discuss the possibility of using the Sgr stream to constrain the dark sector equivalence principle.