Spitzer Space Telescope - General Observer Proposal #80103


An ultra-deep Spitzer look at the most distant galaxy cluster

Principal Investigator: Raphael Gobat
           Institution: Commissariat a l'Energie Atomique (CEA)

     Technical Contact: Raphael Gobat, Commissariat a l'Energie Atomique (CEA)

Co-Investigators: 
Veronica Strazzullo, CEA Saclay                                       
Emanuele Daddi, CEA Saclay                                            
Masato Onodera, ETH Zurich                                            
Marcella Carollo, ETH Zurich                                          
Alvio Renzini, INAF-Padova                                            
Alexis Finoguenov, UMBC                                               
Mark Dickinson, NOAO                                                  
Andrea Cimatti, University of Bologna                                 
Nobuo Arimoto, NAOJ                                                   

Science Category: galaxy clusters and groups(high-z) 
 Observing Modes: IRAC Post-Cryo Mapping
  Hours Approved: 18.1 

Abstract:
We propose to obtain very deep IRAC imaging in the 3.6 and 4.5 micron passbands
on the recently discovered Cl J1449+0856, the most distant galaxy cluster to
date, at z=2.07. This very distant cluster is different from z>2 proto-clusters
in that it shows both an X-ray emission and a significant population of
quiescent galaxies, suggesting an evolved state despite its high redshift. It
thus offers a unique opportunity of studying galaxy evolution in overdense
environments at early cosmic times. The proposed observations will probe for the
first time the rest-frame near-infrared emission of faint cluster galaxies at
z~2, allowing us to determine the stellar mass function at a cosmic epoch which
is thought to be critical for witnessing ongoing stellar mass assembly in
cluster galaxies. These data will be a crucial counterpart of the already
available deep HST NICMOS and WFC3 photometry in identifying cluster members.
Moreover, the deep rest-frame near-infrared photometry will be a fundamental
tool in disentangling the red cluster galaxy population in its two components of
truly quiescent objects and heavily reddened star forming sources. The proposed
observations will thus allow us to take full advantage of the unique discovery
of Cl J1449+0856 to test different scenarios for the evolution of cluster
galaxies at a still unprobed epoch.