Spitzer Space Telescope - Directors Discretionary Time Proposal #252


Ultradeep IRS Spectroscopy in GOODS South

Principal Investigator: Harry Teplitz
           Institution: Spitzer Science Center

Co-Investigators: 
Lee Armus, SSC                                                        
Ranga-Ram Chary, SSC                                                  
David Frayer, SSC                                                     
Andrew Blain, Caltech                                                 
Henrik Spoon, Cornell University                                      
Vassilis Charmandaris, Univ. of Crete                                 
Alexandra Pope, University of British Columbia                        
Douglas Scott, University of British Columbia                         
Ski Antonucci, UCSB                                                   

Science Category: high-z galaxies (z>0.5) 
 Observing Modes: IrsMap IrsStare 
  Hours Approved: 31.6 

Abstract:
Currently approved (GO-2) spectroscopic Spitzer surveys of sub-mm
sources are limited to flux densities brighter than f_24~0.3 mJy.  To
study the dominant population of IR-luminous galaxies (10^11 - 10^12
Lsun at 1<z<3), requires us to attempt spectroscopy of sources a
factor of fainter, at the 0.1 mJy level.  The IRS has never obtained
spectra of an object that faint, so potential systematic limitations
remain unknown.  Nonetheless, understanding the nature of IR-luminous
sources at high redshift is a fundamental piece of the galaxy
evolution puzzle.  To disentangle the AGN and starburst contribution
to the luminosity of such sources requires measurement of the MIR
spectral features (PAH, silicates, etc).  We propose observations of
two faint (~0.15 mJy) soures in the Southern GOODS field.  One target
is a typical LIRG at z=1.09;  the other is a soft-band Chandra source
at z=2.69, with a high LIR/Lx indicating that it may contain a strong
starburst.  We request 31.6 hours of DD time in order to perform the
observations and analysis in time to publicize the results in advance
of GO-3.  We will make our initial analysis available in November on
the SSC website and in a poster at the SSC science conference.