Spitzer Space Telescope - General Observer Proposal #50305


Mid-IR spectroscopy of hot and dusty, luminous high-z star forming galaxies

Principal Investigator: Scott Chapman
           Institution: Caltech

     Technical Contact: Scott Chapman, Caltech

Co-Investigators: 
Andrew Blain, Caltech                                                 
Karin Menendez-Delmestre, Caltech                                     
Bruno Letarte, Caltech                                                
George Helou, SSC                                                     
Ian Smail, Durham                                                     
Rob Ivison, ROE, Edinburgh                                            
David Trethewey, Cambridge, IoA                                       
Mark Swinbank, Durham                                                 

Science Category: ULIRGS/LIRGS/HLIRGS 
 Observing Modes: IrsStare IrsPeakupImage 
  Hours Approved: 53.8 

Abstract:
We have identified a population of high-redshift microJy radio sources which
have rest-UV/optical spectra characteristic of dusty luminous starbursts, and
whose radio emission implies ~1000M/yr star formation rates, but which have no
detectable submm emission from cool dust. These galaxies have S(24um)=0.1-1mJy
similar to submm galaxies, and typically have enormous molecular gas reservoirs
(confirmed through CO3-2 detections). Resolved radio morphologies with 3kpc
scale sizes completes the picture: we propose that these "optically faint radio
galaxies" (OFRGs) are a new class of luminous dusty starburst with hotter dust
temperatures than the similarly high-redshift ultraluminous submm galaxies. We
propose Spitzer-IRS to observe the 10 confirmed star-forming OFRGs in our
accepted molecular gas CO(3-2) study at the IRAM Plateau-de-Bure interferometer.
We will probe the intense mid-IR emission from these galaxies for signatures of
their power source, and to understand whether the aromatic features are
sensitive to the more intense ionization fields in OFRGs compared with SMGs.