Spitzer Space Telescope - Guaranteed Time Observer Proposal #50539


A Multi-wavelength Study of Nearby Galaxies Based on Molecular Line Surveys:
MIPS Observations

Principal Investigator: Giovanni Fazio
           Institution: Harvard-Smithsonian Astrophysical Observatory

     Technical Contact: Zhong Wang, Smithsonian Astrophysical Observatory 

Co-Investigators: 
Erik Rosolowsky, CfA                                                  
Howard Smith, CfA                                                     
Thomas J. Cox, CfA                                                    
Michael Pahre, CfA                                                    
Eric Keto, CfA                                                        
Stephanie Bush, CfA                                                   

Science Category: nearby galaxies (z<0.05, v_sys<15,000 km/s) 
 Observing Modes: MipsPhot 
  Hours Approved: 4 

Abstract:
Dense molecular gas, warm dust, and hot ionized gas are different components of
the multi-step transformation of cold gas into stars and star clusters. While
empirical laws on star formation in galaxies have been established based on
global measurements of these components, substantial galaxy-to-galaxy variations
still exist and remain unexplained. To understand the mechanisms that induce and
regulate star formation and thus galaxy evolution, we need to study processes on
the local scales of typical star forming regions and giant molecular clouds. In
a set of pilot studies, we analyzed the Spitzer and Galex data of nearby giant
spirals M31, M33 and M99, and compared with the new interferometric CO maps of
matching angular resolution. We found evidence that variations in local
condition, environmental effects, and viewing geometry may explain much of the
large scatter in the empirical relationships. Based on the success of this
initial investigation, we have collected high- resolution CO images of 63
late-type galaxies from several large surveys, and we are working on obtaining a
complete set of Spitzer and Galex data for these galaxies. A companion Spitzer
archival research program will re-examine the existing observations along with
CO, HI, UV and optical data, focusing on correlations in spatially resolved,
individual star-forming regions. Here we propose MIPS imaging of the 11 galaxies
in our CO sample that have not already been observed by Spitzer. A GO proposal
will request IRAC time for these galaxies, which are a significant addition to
our study because they substantially increase the fraction of gas-rich late
types in the full sample. Insight from this program will be applicable to not
only nearby system, but also high red-shift galaxies for which only integrated
quantities are measurable.