Spitzer Space Telescope - General Observer Proposal #3360


The Connection between ULXs and Infrared Star-Forming Regions in the
Merging Pair of Galaxies NGC 4485/90

Principal Investigator: Edward Colbert
           Institution: Catholic University of America

Co-Investigators: 
Ann Hornschemeier, Johns Hopkins University                           
Timothy Roberts, University of Leicester                              
Sangeeta Malhotra, Space Telescope Science Institute                  
Martin Ward, University of Leicester                                  

Science Category: interacting/merging galaxies 
 Observing Modes: IracMap IrsMap 
  Hours Approved: 9.3 

Abstract:
We propose IRAC imaging of the starburst galaxy system NGC 4485/90,
and pointed IRS spectral mapping for eight locations within the
galaxies.  NGC 4485/90  houses an extraordinarily large number of
Ultra-luminous X-ray sources (ULXs), and has a dense array of HII
star-forming (SF) regions.  We will use IRAC images to study
correlation statistics between the the six ULXs and nearby IR-luminous
SF regions.  The IRS spectral mapping data is to be taken for
rectangular regions centered on the six ULXs, and for two comparison
regions in NGC 4490.  These spectra will be used to measure physical
characteristics (e.g.  density, excitation) of the gas in the SF
regions and to diagnose properties (e.g.  luminosity, hardness) of the
components of the ionizing radiation.  Our proposed Spitzer
observations will help distinguish between competing models for ULXs,
and will greatly complement on-going X-ray spectral diagnostic work,
which is currently only possible for very X-ray bright ULXs.