Spitzer Space Telescope - General Observer Proposal #50183


Starburst or AGN dominance in submm-luminous candidate AGN

Principal Investigator: Kristen Coppin
           Institution: Durham University

     Technical Contact: Kristen Coppin, Durham University

Co-Investigators: 
Alexandra Pope, NOAO                                                  
James Dunlop, ROE                                                     
Rob Ivison, UK-ATC, ROE                                               
Dave Alexander, Durham                                                
Simon Dye, Cardiff                                                    
Dave Clements, Imperial College London                                
Michael Rowan-Robinson, Imperial College London                       
Mark Swinbank, Durham                                                 
Karin Menendez-Delmestre, Caltech                                     
Andrew Blain, Caltech                                                 
Ian Smail, Durham                                                     
Scott Chapman, Cambridge                                              
Douglas Scott, UBC                                                    
Loretta Dunne, Nottingham                                             
David Hughes, INAOE                                                   
Itziar Aretxaga, INAOE                                                
Sebastian Oliver, Sussex                                              
Mat Page, University College London                                   
Duncan Farrah, Cornell                                                
Mattia Vaccari, Padova                                                
Eelco van Kampen, Innsbruck                                           
Sungeun Kim, Sejong                                                   

Science Category: high-z galaxies (z>0.5) 
 Observing Modes: IrsMap IrsStare IrsPeakupImage 
  Hours Approved: 58.4 

Abstract:
It is widely believed that starbursts/ULIRGs and AGN activity are triggered by
galaxy interactions and merging; and sub-mm selected galaxies (SMGs) seem to be
simply high redshift ULIRGs, observed near the peak of activity. In this
evolutionary picture every SMG would host an AGN, which would eventually grow a
black hole strong enough to blow off all of the gas and dust leaving an
optically luminous QSO. In order to probe this evolutionary sequence, a crucial
sub-sample to focus on would be the "missing link" sources, which demonstrate
both strong starburst and AGN signatures and to determine if the starburst is
the main power source even in SMGs when we have evidence that an AGN is present.
The best way to determine if a dominant AGN is present is to look in the mid-IR
for their signatures, since often even deep X-ray observations miss identifying
the presence of AGN in heavily dust-obscured SMGs. We have selected a sample of
SMGs which are good candidates for harboring powerful AGN on the basis of their
IRAC colours (S8um/S4.5um>2). Once we confirm these SMGs are AGN-dominated, we
can then perform an audit of the energy balance between star-formation and AGN
within this special sub-population of SMGs where the BH has grown appreciably to
begin heating the dust emission. The proposed observations with IRS will probe
the physics of how SMGs evolve from a cold-dust starburst-dominated ULIRG to an
AGN/QSO by measuring the level of the mid-IR continuum, PAH luminosity, and Si
absorption in these intermediate `transitory' AGN/SMGs.