Spitzer Space Telescope - Archive Research Proposal #40773


Mapping Molecular Hydrogen Excitation and Mass in Nearby Galaxies from the SINGS
Archive

Principal Investigator: Gregory Brunner
           Institution: Rice University

     Technical Contact: Gregory Brunner, Rice University

Co-Investigators: 
Reginald Dufour, Rice University                                      
Kartik Sheth, Spitzer Science Center                                  
Stuart Vogel, University of Maryland                                  
Mark Wolfire, University of Maryland                                  

Science Category: nearby galaxies (z<0.05, v_sys<15,000 km/s) 
Dollars Approved: 96765 

Abstract:
Molecular hydrogen (H2) is inherently connected with the evolution of a galaxy
through a variety of processes. In galaxies, H2 traces star formation in nuclear
regions, near the ends of bars in barred spirals, and along spiral arms where
star formation is triggered by the passage of a spiral density wave. The SINGS
legacy program has used the Spitzer Infrared Spectrograph (IRS) long-low module
(LL; 14 - 38 microns) in spectral mapping mode to map large strips across 65
galaxies ranging in Hubble type, star-formation rate, and nuclear activity. We
propose to use the SINGS LL data cubes to map the spatial distribution of warm
(T = 100 - 300 K) H2, traced by the H2 S(0) (28.2 micron) and H2 S(1) (17.0
micron) lines, in 18 SINGS galaxies that have also been observed in CO (J = 1 -
0) emission through the Berkeley-Illinois-Maryland Array Survey of Nearby
Galaxies (BIMA SONG). We have developed unique software that creates spatially
resolved maps of extremely faint and blended spectral lines from Spitzer IRS LL
data cubes. Using our software, we propose to map H2 S(0) and H2 S(1) emission
across each galaxy and use these two lines to model variations in the H2
excitation and mass across each galaxy. We will distinguish the H2 excitation
mechanism as a function of position across each galaxy by comparing the H2 maps
to CO emission (from SONG) and maps of mid-infrared spectral diagnostics such as
the [O IV](25.89 micron) line (a shock diagnostic) and the [S III](18.71
micron)-to-[S III](33.48 micron) line ratio (an HII region electron density
diagnostic). We will also compare H2 spatial variations to UV and optical
imagery (U, B, V, R, and H(alpha)) for additional insight into the H2 excitation
mechanisms and to correlate H2 properties with the ages, masses, and star
formation rates of stellar clusters and associations across the sample of SINGS
galaxies.