Spitzer Space Telescope - General Observer Proposal #40918


Spitzer IRS Identification of Distant Compton-Thick AGN in GOODS-N

Principal Investigator: David Alexander
           Institution: Durham University

     Technical Contact: David Alexander, Durham University

Co-Investigators: 
Ranga-Ram Chary, SSC                                                  
Mark Dickinson, NOAO                                                  
David Elbaz, CEA/Saclay                                               
David Frayer, SSC                                                     
Minh Huynh, SSC                                                       
Alexandra Pope, NOAO                                                  

Science Category: AGN/quasars/radio galaxies 
 Observing Modes: IrsStare 
  Hours Approved: 72.9 

Abstract:
Deep X-ray surveys have identified large numbers of Active Galctic Nuclei (AGN)
in a relatively obscuration-independent manner. However, there is considerable
evidence that >50% of luminous AGNs are unidentified in even in the deepest
X-ray surveys, most likely due to Compton-thick or near Compton-thick absorption
of the intrinsic X-ray emission. These AGNs should be present in deep Spitzer
surveys due to thermally reprocessed AGN emission by dust in the absorbing
material. Here we propose for Spitzer-IRS spectroscopy of 14 candidate z<1
Compton-thick AGN identified on the basis of "warm" IR colors from the
combination of the ultra-deep Chandra, 24um-MIPS and 70um-MIPS observations in
GOODS-N. We will identify AGN activity in these sources from the presence of
weak PAH emission, a warm IR continuum, and/or a Si 9.7um absorption feature.
These observations will be used to directly quantify the ubiquity of
Compton-thick AGN out to z~1, and to assess their contribution to the IR
background and ``contamination'' to IR-derived estimates of the star-formation
history.