Spitzer Space Telescope - Archive Research Proposal #20407


Gas, Dust, and Star Formation in Wolf-Rayet Galaxies

Principal Investigator: Roy Gal
           Institution: University of California, Davis

Co-Investigators: 
Iranderly Fernandes, Instituto Nacional de Pesquisas Espaciais, Divisao
Aurea Garcia-Rissmann, Laboratorio Nacional de Astrofisica/MCT        
Reinaldo de Carvalho, Instituto Nacional de Pesquisas Espaciais, Divisao

Science Category: starburst galaxies 
Dollars Approved: 66835.0 

Abstract:
Starbursts, and particularly Wolf-Rayet galaxies, are objects with
violent star formation that cannot be maintained for a Hubble time.
They provide important clues to understanding galaxy formation and
evolution mechanisms, since massive stars play an important role in
the nucleosynthesis of heavier elements and the transfer of mechanical
energy to the interstellar medium.  Understanding how gas collapses to
generate bursts of star formation in galaxies, and how star cluster
evolution occurs to form the relation between central black hole mass
and galaxy bulge properties is one of the key subjects in modern
astrophysics.  We propose to use existing high- and low- resolution
IRS observations to investigate the gas properties and stellar
populations of a sample of local Wolf Rayet galaxies, using
mid-infrared diagnostic diagrams.  The mid-IR has the advantage of not
being subject to the huge extinction that affects UV and optical
observations, especially in objects with strong star formation where
the young clusters are embedded in a thick dust shorud.  We will probe
the star formation/AGN processes in these environments through the
analysis of fine structure line ratios, PAH emission and the
derivation of photo-ionization parameters.  These results will be
compared with those derived from spectra available in the SDSS
database and targeted long-slit observations, revealing the
limitations of traditional shorter wavelength observations.  Realistic
photoionization models will be used to analyze a broad range of
physical parameters and peculiarities of the observed regions.
Correlations between the massive stellar spectral signatures and gas
abundance, or gas excitation, will enable estimation of the number of
such stars in the observed regions.  The heterogeneous character of
the sample, including active and non-active galaxies, will allow us to
test evolutionary scenarios proposed for AGN, an important test for
the Unified Model of AGN.