Fall 2013 Physics Colloquium
October 4; PAS 224, 3pm
Chris Impey
University of Arizona
Probing the Limits of Nuclear Activity with the COSMOS Survey
The Cosmological Evolution Survey (COSMOS) involves the largest contiguous region of the sky ever imaged by HST.
It was motivated by the study of galaxy evolution and morphology but the combination of depth, breadth and extensive multiwavelength
data makes it the best region in the sky for a comprehensive study of AGN. Using deep X-ray data in the field, over 800 AGN have been
spectroscopically confirmed, and the survey has particular sensitivity to low black hole mass, low accretion rates, and high levels of obscuration.
A limiting accretion rate of L/L_Edd = 0.01 is seen, below which the flow may be advective. Analogs to the Milky Way black hole at z = 2 can be detected.
A study of host galaxies suggests that the AGN triggering occurs on kiloparsec scales within the host. Fitting SEDs shows that the spectral components
are predictable enough to efficiently select AGN below the limit of spectroscopy on large telescopes, extending this work to even lower black hole masses.
The eventual goal is a complete census of intermediate mass black holes at redshifts 1-3, which is required to tell the complete story of the co-evolution
of galaxies and black holes.