Probing the IR Cirrus: Small-Scale Structure and Molecular Content

Details Probing the IR Cirrus: Small-Scale Structure and Molecular Content Probing the IR Cirrus: Small-Scale Structure and Molecular Content

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40183d&link_type=abstract

Spitzer Proposal ID #40183

Physics

Scientific paper

The infrared cirrus is a network of diffuse interstellar clouds seen over ~50% of the sky at high Galactic latitudes. The cirrus has not yet been studied by Spitzer, yet there are several compelling scientific reasons to do so. First, the cirrus appears to contain a substantial amount of molecular hydrogen. A correlation is seen to exist between the column density of H2 seen in absorption toward extragalactic sight lines and the 100um cirrus emission adjacent to those sight lines. However, the low spatial resolution of existing all-sky IR maps and likely variation of cirrus structure on angular scales >5' introduces a great deal of scatter into the correlation. Using cirrus flux as a proxy for H2 column density will allow us to correct large-scale HI surveys for the 'missing' molecular contribution and get accurate measurements of the total mass in this diffuse ISM phase. Second, the cirrus may delineate the disk-halo interface and be a site of enhanced cooling (via H2 rotational excitation) and triggered star formation. Detailed studies of cirrus morphology at small scales (<1') can tell us a great deal about the physical structure of the cirrus: thickness, particle density, and cooling rates. Additionally, small-scale cirrus structure is a significant Galactic foreground that needs to be understood and characterized for future cosmology probes such as Planck and ALMA. We propose a set of Spitzer observations of seven high-latitude fields around AGN to address these two science drivers. MIPS observations at 70 and 160um will map the cirrus at unprecedented resolution while 24um and IRAC 8um fields will map the brightest dust and PAH emission.

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