Active star formation in Infrared Dark Clouds

Details Active star formation in Infrared Dark Clouds Active star formation in Infrared Dark Clouds

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006sptz.prop30123j&link_type=abstract

Spitzer Proposal ID #30123

Computer Science

Scientific paper

We propose to use the Spitzer Space Telescope to obtain MIPS SED and IRS observations toward a sample of compact cores within Infrared Dark Clouds (IRDCs), a new class of objects recently identified as mid-infrared extinction features in the Galactic plane. We have identified 10,961 IRDCs in the Galaxy, and using 13CO molecular line emission maps, have obtained reliable kinematic distances to 312. We have selected the 38 darkest of these clouds for further study. Our molecular line and millimeter continuum data suggest that IRDCs are the cold molecular precursors to cluster-forming clumps. Each IRDC contains several dense, cold compact cores with masses of 10-2,100 Msun. From IRAC images we find that 1/3 of these cores show extended, diffuse 3-8 micron emission, with an apparent enhancement in the 4.5 micron band. In addition, each of these cores is coincident with a bright 24 micron emission source in MIPS images and shows broad linewidths in high-density tracing molecular lines, suggesting they are sites of active star formation. Combined with mm/sub-mm data, the SEDs for these active cores reveal very large bolometric luminosities (~16,000 Lsun). Despite similar 1.2 mm fluxes, many cores show no 24 micron emission, suggesting that they are more quiescent. We request a total of 38.2 hours to obtain MIPS SED measurements of 80 IRDC cores and IRS 5-14 micron spectroscopy of 20 sources showing an enhancement at 4.5 microns. The 55-95 micron SEDs will establish accurate 24 micron to 1.2 mm SEDs, bolometric luminosities, masses, dust temperatures, and emissivity indices for the cores. The IRS spectroscopy will definitively distinguish whether the 4.5 micron enhancement arises from shocked molecular hydrogen, or whether it is due to an extincted continuum source.

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