Spitzer Space Telescope - Guaranteed Time Observer Proposal #50666


A systematic IRS survey of the Spitzer 70 micron extragalactic population

Principal Investigator: Duncan Farrah
           Institution: Cornell University

     Technical Contact: Duncan Farrah, Cornell University

Co-Investigators: 
James Houck, Cornell                                                  
Carol Lonsdale, Virginia                                              
Maria Polletta, IAP, Paris                                            
Henrik Spoon, Cornell                                                 
Dan Weedman, Cornell                                                  

Science Category: intermediate-z galaxies (0.05<z<0.5) 
 Observing Modes: IrsStare 
  Hours Approved: 89.9 

Abstract:
We propose a systematic IRS survey of a complete sample of 68 extragalactic
sources with 70 micron fluxes brighter than 20mJy. Recent theoretical and
observational results suggest that the Spitzer extragalactic 70 micron
population is very important; results from source counts and SED modeling
suggest that 70 micron sources at these fluxes are mainly obscured starbursts
over 0<z<8 with small numbers of dusty AGN, but small-scale IRS programs
targeting 70 micron selected sources suggest that this population is
surprisingly heterogeneous, with a wide dispersion in mid-IR spectral shapes
(from power laws to PAH dominated) and covering a very wide redshift range
(0.1<z<2.0). The Spitzer 70 micron population may thus be a critical unknown in
understanding the dramatic evolution of LIRGs over 0<z<2. To date however, there
has been no thorough mid-IR spectroscopic followup of 70 micron selected
samples. This represents a major gap in our knowledge, as Herschel-PACS will
discover large numbers of 70 micron sources, and is one that can only be filled
by Spitzer before cryogen exhaustion. Our program will constitute the first
systematic IRS followup of the extragalactic 70 micron population.