Astrophysics and Relativity Seminars

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 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.

December 11, 2009 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

Jennifer Siegal-Gaskins
Ohio State

Using anisotropy to identify a dark matter signal in diffuse gamma-ray emission with Fermi

Dark matter annihilation in Galactic substructure will produce diffuse gamma-ray emission of remarkably constant intensity across the sky, making it difficult to disentangle this Galactic dark matter signal from the extragalactic gamma-ray background. Recent studies have considered the angular power spectrum of the diffuse emission from various extragalactic source classes and from Galactic dark matter. I'll discuss these results and show how the energy dependence of anisotropies in the total measured diffuse emission could be used to confidently identify a signal from dark matter in Fermi data. Finally, I'll present new results demonstrating that anisotropy analysis could significantly extend the sensitivity of current indirect dark matter searches.

January 22, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

January 29, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

Vincent Desjacques
Institute for Theoretical Physics, Zurich

TBA

February 5, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

February 12, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

February 19, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

February 26, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

March 5, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

March 12, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

March 26, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

April 2, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

April 9, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

April 16, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

April 23, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD

April 30, 2010 Friday 2:30 PM 
Meyer 5th Fl. CCPP Lounge
Astrophysics and Relativity Seminars (astro)

TBD TBD
TBD