Spitzer Space Telescope - General Observer Proposal #40784


Cluster Environmental Effects on Galaxy Evolution at z=0.2 (Abell 963 vs. Abell
2192)

Principal Investigator: Aeree Chung
           Institution: National Radio Astronomy Observatory (NRAO)

     Technical Contact: Aeree Chung, NRAO

Co-Investigators: 
Min S. Yun, University of Massachusetts, Amherst                      
J. H. van Gorkom, Columbia University                                 
G. Morrison, Institute for Astronomy, University of Hawaii            
Marc Verheijen, Kapteyn Astronomical Institute, University of Gron    
A. Szomoru, Joint Institute for VLBI in Europe                        
K. S. Dwarakanath, Raman Research Institute                           
B. M. Poggianti, INAF - Padova Astronomical Observatory               
D. Schiminovich, Columbia University                                  

Science Category: intermediate-z galaxies (0.05<z<0.5) 
 Observing Modes: IracMap MipsScan 
  Hours Approved: 30.4 

Abstract:
We propose Spitzer IRAC and MIPS observations for two carefully selected
clusters at z=0.2. This is the lowest redshift where the Butcher Oemler effect
has been seen and the highest redshift where HI imaging is feasible with current
instrumentation. Abell 963 is a rich and X-ray luminous cluster with an
unusually high fraction of blue galaxies while Abell 2192 is less massive and
has more substructure. To address the question of how galaxies get affected by
the surroundings, we will investigate star formation and gas properties of
galaxies in those two clusters as a function of environment. Using the Spitzer
data, we will study star-forming or AGN activities, star formation histories,
and dust contents. We are building up a multiwavelength database on the two
clusters. Specifically, we have been allocated 2000 hrs of WSRT time to image
the clusters in HI and 250 hrs of FCRAO time to determine the CO content of the
cluster galaxies. We are also obtaining optical imaging and spectroscopy data.
This unique dataset will allow us to relate star formation rates and histories
directly to the gas content and stellar populations for the first time at this
redshift. In addition, we will probe not only galaxies in the two clusters but
also fore/background systems, using the huge velocity coverages of the HI and CO
observations. In order to trace galaxies with normal star formation rates (1-2
Msun/yr) with S/N>5 in all four IRAC bands and 24/70 microns, we request 3.4
hours of IRAC and 11.8 hours of MIPS observation time on each cluster, yielding
30.4 hours of the integration time in total.