Spitzer Space Telescope - General Observer Proposal #60121


Cadenced IRAC Monitoring of Infrared-Variable AGNs, Part III 

Principal Investigator: Matthew Ashby
           Institution: Harvard-Smithsonian Astrophysical Observatory

     Technical Contact: Matthew Ashby, Harvard-Smithsonian Astrophysical Observatory

Co-Investigators: 
Joseph Hora, Harvard-Smithsonian CfA                                  
Morgan Fouesneau, University of Strasbourg                            
Jessica Krick, Spitzer Science Center/CalTech                         
Jason Surace, Spitzer Science Center/CalTech                          
Howard Smith, Harvard-Smithsonian CfA                                 
Leonidas Moustakas, Jet Propulsion Laboratory                         

Science Category: AGN/quasars/radio galaxies 
 Observing Modes: IRAC Post-Cryo Mapping
  Hours Approved: 8.0 

Abstract:
We have analyzed IRAC imaging data from all 109 Spitzer visits to a very
well-studied field, the IRAC Dark Calibration Field (IRAC-CF) near the north
ecliptic pole. With this extensive dataset, we have already identified a unique
sample of 30 IR-variable galaxies for which we are now working to characterize
the variability amplitudes and timescales, panchromatic SEDs, and host
morphologies, among other quantities. Unfortunately, the continual change in
spacecraft roll angle means that our sources are typically observed for at most
six months at a time by both IRAC FOVs in succession -- in other words, the
visibility windows are exactly out of phase. Thus the planned Cycle 6 IRAC
calibration observations, without the additional coverage our proposal would
provide, will present large, unavoidable gaps that frustrate the time-delay
analysis we wish to perform on exactly the timescales known to be typical of
active galaxies. Since 2007 July, we have carried out cadenced IRAC observations
in synchrony with the IRAC-CF dark-calibration observations as part of our
approved Cycle 4 and 5 programs. We propose to continue this unique AGN
monitoring campaign into 2010. The resulting timelines (covering 2000 days thus
far and expected to run ultimately to more than 2400 days), are a unique legacy
of the Spitzer mission. This dataset, especially for the sizable unbiased AGN
sample we now have, holds unique promise for measuring the colors and
temperatures of IR-varying AGN, and will have much to say about the underlying
physical models of the infrared AGN emission. Accordingly, we ask for just 8 h
to gather IRAC photometry in the temporal gaps that would otherwise accrue in
Cycle 6.