Computer Science
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20658v&link_type=abstract
Spitzer Proposal ID #20658
Computer Science
Scientific paper
We propose an investigation of the molecular hydrogen component of normal spiral galaxies using the S(0) line at 28 microns. ISO observations have shown that the S(0) line probes moderately warm (about 100K) molecular gas which can contain significant mass, in particular in the outer regions of galaxies. In addition, it was found that even small quantities of warm gas can significantly affect the CO-H2 mass conversion factor. With the unprecendented sensitivity of IRS on SST we can now study in detail the warm H2 component, its mass, scale length, and temperature structure, as a function of environmental parameters such as position in a galaxy (arm or interarm location), galactocentric radius, and local metallicity and radiation field. We propose to use IRS to take deep spectra of the H2 S(0) line at intervals of 30 arcseconds over (a) the inner disk of the Local Group spiral galaxy M33 (30 positions in total) where we will have excellent spatial resolution across spirals arms and (b) the northern half of the normal quiescent gas-rich edge-on Sc galaxy NGC5907 (17 positions in total), where we will probe from the nucleus all the way to the end of the HI disk. In both of these galaxies we have excellent matching CO, HI and [CII] 158 micron data available, which are important for the interpretation of the results. While the S(0) line will not probe the cold bulk H2, we will pick up warm H2, also in regions where CO is dissociated. This is expected to occur in cloud envelopes and in regions of low metallicity, such as in the outer disks of galaxies. Recent star formation in the extreme outer disks shows that H2 must be there, yet CO is no detected. ISO observations have also shown that that the disk scale-length in the S(0) line is much larger than that of CO. The IRS observations will go more than 10 times deeper than ISO, and will allow us to pick up even small column densities of warm H2, giving us a much better understanding of the molecular hydrogen component of normal spiral galaxies.
Cannon John
Israel Frank
Papadopoulos Padelis
Skillman Evan
Spaans Marco
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