Spitzer Space Telescope - General Observer Proposal #20369


Spitzer Imaging and Spectroscopy of Collisional Ring Galaxies

Principal Investigator: Philip Appleton
           Institution: Caltech

Co-Investigators: 
Lee Armus, SSC-Caltech                                                
Joseph Mazzarella, IPAC-Caltech                                       
Barry Madore, Carnegie Observatories (OCIW)                           
Curtis Struck, Iowa State University                                  
Seppo Laine, SSC-Caltech                                              
Thomas Jarrett, SSC-Caltech                                           
Beverly Smith, East Tennessee State University                        
Armando Gil de Paz, Carnegie Observatory (OCIW)                       
William Reach, SSC-Caltech                                            
Vassilis Charmandaris, Cornell University                             
Steven Lord, HSC-Caltech                                              
Kirk Borne, George Mason University                                   

Science Category: interacting/merging galaxies 
 Observing Modes: IracMap IrsMap IrsStare MipsPhot 
  Hours Approved: 12.0 

Abstract:
We propose Spitzer imaging and IRS spectroscopy of a sample of twelve
collisional ring galaxies.  These galaxies exhibit radially-expanding
massive- star forming rings which are believed to be the gravitational
response of the target disk to a head-on collision of a companion
through its center.  Among the most luminous kinds of galaxy found by
GALEX in the UV, these collisional systems are particularly suitable
for studying interstellar dust under a wide variety of excitation
conditions and metallicities.  Spitzer imaging and MIR-spectroscopy,
in combination with a large body of ancillary data and models, will
allow us to:  1) determine the SEDs of massive star formation knots
around the rings from the UV to the far-IR, and 2) investigate how the
properties of dominant dust grain populations vary with the large
range of conditions seen in the rings, 3) investigate how the strength
of PAH--features varies with metallicity, and 4) search for (dust
enshrouded) secondary star formation sites inside the rings predicted
to be triggered by the collapse of molecular clouds in the wake of the
ring passage.  Understanding the response of dust grains to a wide
range of excitation conditions in collisional systems will contribute
to our understanding of the rest-frame mid-IR properties of high
redshift galaxies seen in deep Spitzer surveys.