Spitzer Space Telescope - General Observer Proposal #3294


Environmental drivers of galaxy evolution:  IR-derived star formation
rates in the Abell 901/902 supercluster

Principal Investigator: Eric Bell
           Institution: Max-Planck-Institute fuer Astronomie

Co-Investigators: 
Christian Wolf, University of Oxford, UK                              
Klaus Meisenheimer, Max-Planck-Institute fuer Astronomie              
Hans-Walter Rix, Max-Planck-Institut fuer Astronomie                  
Casey Papovich, University of Arizona                                 
Meghan Gray, University of Nottingham, UK                             
Michael Balogh, University of Durham/ University of Waterloo          
Rachel Somerville, STScI                                              

Science Category: galaxy clusters and groups 
 Observing Modes: IracMap MipsScan 
  Hours Approved: 39.0 

Abstract:
The environment in which a galaxy resides shapes its star formation
(SF) history and present-day SF rates.  Huge efforts have addressed
this critical issue, primarily using optical emission-lines;  these
efforts find that SF is suppressed in dense environments.  However,
limited radio and IR data tentatively suggest that mergers, tidal
interactions and ram-pressure effects can drive intense bursts of
obscured SF, which are overlooked by optical observations.  We propose
deep MIPS and IRAC observations of a 0.5x0.5 degree field encompassing
the Abell 901/902 supercluster region in order to explore the amount,
distribution, and physical drivers of obscured SF in a wide range of
environments.  From our ultra-precise delta z=0.02 COMBO-17
photometric redshift catalog (1200  cluster members and >10000
background galaxies), we know that the Abell 901/902 supercluster has
three dense sub-clusters connected by a low-density filamentary
network, allowing characterization of obscured SF over a wide range of
densities in a single field.  From deep X-ray and weak lensing data,
we also know that the X-ray luminosity to dark-matter density ratio
varies from sub-cluster to sub-cluster, giving powerful leverage to
differentiate between ram-pressure and tidal influences on obscured
SF.  In this 39hr proposal, we will study obscured SF down to roughly
LMC luminosities (likely reaching 95 per cent of total cluster SF) in
A901/902 using near-confusion-limited MIPS 24um data (where 70  and
160  data will help constrain SED shape for brighter galaxies).  IRAC
data is requested to pin down precise positions to attach redshifts to
MIPS detections.  Using these data we will address:  Is SF always
suppressed by dense environments, or is there a moderate density
regime where SF is acutally enhanced?  In which environments is the
bulk of SF at the current epoch?  How much SF in dense environments is
heavily obscured?  Do ram-pressure or tidal effects lead to obscured
SF?