Spitzer Space Telescope - General Observer Proposal #30119


Infrared Emission from the Smallest Active Galaxies

Principal Investigator: Aaron Barth
           Institution: University of California, Irvine

Co-Investigators: 
Jenny Greene, Harvard-Smithsonian Center for Astrophysics             
Luis Ho, Observatories of the Carnegie Institution of Washi           

Science Category: AGN/quasars/radio galaxies 
 Observing Modes: IrsStare 
  Hours Approved: 26.1 

Abstract:
Virtually all of our current knowledge of black hole demographics,
both in nearby inactive galaxies and in AGNs, comes from observations
of black holes with masses between a few million and a few billion
solar masses in host galaxies with stellar velocity dispersions
between about 70  and 400  km/sec.  Searching for smaller black holes
in low-mass galaxies can yield important clues to the origin and early
evolution of supermassive black holes, and AGN surveys are the best
available way to identify such objects.  Using the Sloan Digital Sky
Survey, we have identified 19 Seyfert 1 galaxies with black hole mass
below 10^6 solar masses (Greene & Ho 2004), and 20  Seyfert 2 galaxies
having stellar velocity dispersions smaller than 70  km/sec as
determined by new Keck observations.  These AGN samples offer a unique
opportunity to study the very early growth stages of black holes and
their host galaxies.  Spitzer observations of mid-infrared emission
will be the best available calorimeter of the energetics of these tiny
AGNs.  Our primary goal is to determine the infrared contribution to
the bolometric luminosities, which will be a key to understanding the
black hole accretion rates.  From the infrared spectral shapes we will
constrain the dust temperatures and search for silicate features in
emission or absorption that may indicate the presence of an obscuring
torus, and which will help to determine whether the Type 1 and Type 2
objects differ primarily as a result of our viewing angle, as in
classic AGN unified models.  PAH features and narrow emission lines
will be used to diagnose the relative contributions of AGN and star
formation to the infrared luminosity.  To accomplish these goals, we
request IRS staring-mode spectroscopy in the SL2, SL1, LL2, and LL1
settings for our Sloan-selected sample of 19 Seyfert 1s and 20
Seyfert 2s, as well as NGC 4395 and POX 52, which are the prototypical
nearby examples of Seyfert nuclei in dwarf host galaxies.