Spitzer Space Telescope - General Observer Proposal #30407


The Astrophysics of OH Megamasers in Merging Galaxies:  the Role of
Star Formation, Dust, Molecules, and AGN

Principal Investigator: Jeremy Darling
           Institution: University of Colorado

Co-Investigators: 
Lee Armus, Spitzer Science Center                                     
Vassilis Charmandaris, University of Crete                            
Ylva Pihlstrom, University of New Mexico                              
Henrik Spoon, Cornell University                                      

Science Category: ULIRGS/LIRGS/HLIRGS 
 Observing Modes: IrsPeakupImage IrsStare 
  Hours Approved: 25.5 

Abstract:
OH megamasers (OHMs) are starburst-scale masers associated with
merging galaxies that can trace star formation, the formation of
binary massive black holes, and possibly the feedback process between
starbursts and black hole accretion in nascent quasars.  We lack a
physical understanding of the mechanisms and conditions responsible
for the OHM process, and the physical conditions distinguishing OHM
hosts from non-masing (ultra)luminous infrared galaxies ([U]LIRGs)
have not been identified.  Understanding the astrophysics of OHMs is
critical to employing them as tracers of black hole and galaxy
evolution at high redshift.  Spitzer IRS spectra provide a rich set of
diagnostics of dust phases, AGN influence, and the molecular ISM, all
at scales well matched to the regions responsible for maser activity.
We propose to obtain both high and low resolution IRS spectra of a
flux-limited sample of 28 OHM hosts and compare the physical
properties derived from the spectra to a sample of (U)LIRGs in the
Spitzer archive.  Combined with ancillary high resolution optical and
radio imaging and spectroscopy, we hope to place the OHMs into the
evolutionary sequence of major mergers and address fundamental
questions about the nature of OHMs such as the source of the maser
pump, the importance of beaming, and whether OHMs require AGN activity
or are simply coincident with it.