Spitzer Space Telescope - General Observer Proposal #20375


Of Starbursts and Monsters:  An IRS High-resolution Spectroscopic
Study of Ultraluminous Infrared Galaxies

Principal Investigator: Lee Armus
           Institution: IPAC

Co-Investigators: 
Vassilis Charmandaris, University of Crete                            
Vandana Desai, Caltech                                                
Henrik Spoon, Cornell University                                      
Lei Hao, Cornell University                                           
Berhard Brandl, Leiden University                                     
Jeronimo Bernard-Salas, Cornell University                            

Science Category: ULIRGS/LIRGS/HLIRGS 
 Observing Modes: IrsStare 
  Hours Approved: 23.6 

Abstract:
Ultraluminous infrared galaxies (ULIRGs) generate the power output of
quasars, but nearly all of this energy emerges in the mid and
far-infrared part of the spectrum.  While rare at low-redshift, ULIRGs
are resposible for the strong evolution in the mid-IR number counts to
z~1, and may dominate the star formation rate density and far-infrared
background at z~2-3.  The GTO ULIRG program is observing a sample of
110  ULIRGs in the local universe with the IRS.  Less than half of
these have observations with the high-resolution IRS modules.  We
propose to observe a sample of 34 ULIRGs from this program in SH
and/or LH in order to search for unambiguous proof of buried AGN (via
the [NeV] emission line), as well as characterize the warm molecular
gas content, the small grain characterisitics and the starburst mass
functions, via the H2, PAH, and [NeII], [NeIII], [OIV], [SIV], and
[SIII] line flux ratios in the SH and LH IRS spectra.  These
observations will double the number of ULIRGs will high quality,
high-resolution IRS spectra in the archive, and significantly increase
the number of ULIRGs observed at z > 0.3, where most of the evolution
in the counts of IR-bright galaxies is occuring.