Spitzer Space Telescope - General Observer Proposal #40132


Dust in the Extremely Metal Poor Galaxy IZw18

Principal Investigator: Alberto Bolatto
           Institution: University of California, Berkeley

     Technical Contact: Alberto Bolatto, University of California, Berkeley

Co-Investigators: 
Adam Leroy, Max Planck Institute for Astronomy - Heidelberg           
Fabian Walter, Max Planck Institute for Astronomy - Heidelberg        
John Cannon, Wesleyan University                                      
Karin Sandstrom, U.C. Berkeley                                        

Science Category: nearby galaxies (z<0.05, v_sys<15,000 km/s) 
 Observing Modes: MipsPhot 
  Hours Approved: 8.0 

Abstract:
IZw18, with one of the lowest nebular metallicities measured to date
(12+log(O/H)=7.2), is perhaps the most important link between primitive galaxies
in the local universe and distant primeval sources. It is also the touchstone of
any theory relating galaxy properties to metallicity. Existing archival MIPS
observations were unsuccessful at detecting IZw18 at 160 um, but detected it at
70 um. We propose to obtain multiepoch deep MIPS observations at these
wavelengths, designed to provide an order of magnitude better sensitivity than
currently available. With a very modest investment of time, we will be able to
measure the dust mass of this galaxy and determine its dust-to-gas ratio. If
these observations resolve the extended atomic envelope of IZw18 we will be able
to constrain the molecular gas content of this galaxy, and study the
relationship between molecular gas and star formation at the lowest
metallicities, providing valuable insights into star formation in the primitive
universe.