Spitzer Space Telescope - General Observer Proposal #30877


A Mid-Infrared Survey of the Warm ISM and Star Formation in Molecular
Gas-Rich Radio Galaxies

Principal Investigator: Aaron Evans
           Institution: Stony Brook University

Co-Investigators: 
Lee Armus, SSC                                                        
Jason Surace, SSC                                                     
Tatjana Vavilkin, Stony Brook University                              
Dean Hines, Space Science Center                                      
Joseph Mazzarella, IPAC                                               
Jeremy Lim, ASIAA                                                     

Science Category: AGN/quasars/radio galaxies 
 Observing Modes: IracMap IrsStare MipsPhot 
  Hours Approved: 19.6 

Abstract:
We propose Spitzer observations to assess the properties of the warm
ISM and star formation in a complete sample of 15 CO-detected, local
radio galaxies.  Eight of these galaxies were detected in CO as part
of a millimeter-wave survey of a complete IRAS flux-limited sample of
33 low-redshift (z <~ 0.1) radio galaxies, and are observed to have
morphologies consistent with major/minor galaxy mergers or
interactions and extended (7-14" = 2-8 kpc) CO disks.  In addition, 7
of the radio galaxies were detected in a recent volume-limited (z <
0.05) CO survey.  The CO luminosities of these galaxies translate into
0.4-7x10^9 M_sun of cold molecular gas (H_2).  Spitzer low and
high-resolution IRS will detect warm H_2 emission, broad PAH emission,
and high ionization lines, enabling (i) a determination of whether the
warm-to-cold H_2 ratio correlates with AGN (e.g., high ionization
lines) or starburst (strong PAH) activity, (ii) a measurement of the
grain size and ionization state of PAH, and (iii) a measure of the
relative contribution of nuclear PAH emission to the mid-IR nuclear
emission.  Spitzer IRAC observations will be used to measure the
luminosity and extent of PAH, and will be compared with the CO maps to
determine if PAH traces star formation.  Finally, MIPS observations
will be combined with IRS/IRAC and 2MASS data, and multi-component
dust models will be fit to the continuum emission so that the
temperature and mass of the dust component(s), and thus the
H_2-to-dust mass ratios, can be calculated.  Data from this proposal
will be compared with archival and GTO data of nearby IR galaxies,
starbursts and other gas-rich systems in order to assess the
relationship of gas-rich radio galaxies with other types of "active"
galaxies.  The IR and CO brightness of the galaxies, and the spatial
extent of molecular disks mapped thus far, makes this the best suited
sample for assessing the properties of the warm ISM and star formation
in luminous AGN with Spitzer.