Computer Science
Scientific paper
Sep 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sptz.prop.3567v&link_type=abstract
Spitzer Proposal ID #3567
Computer Science
Scientific paper
We propose to observe two nearby starburst galaxies with the Spitzer Space Telescope in order to determine the properties of the ultra-dense H II (UDHII) regions in these objects. These compact, radio-bright regions are believed to represent the youngest phase in the evolution of super star clusters, in which a newly-born stellar cluster is still heavily embedded in the natal dust and molecular envelope from which it formed. The inferred sizes and masses of the buried clusters are consistent with those expected for the progenitors of globular clusters. Recent ground-based 10 micron images of He2-10 and NGC5253 reveal that the UDHIIs are extremely luminous in the mid-IR, and are responsible for more than half of the total IRAS flux from these galaxies. Although UDHIIs completely dominate the radio flux of their hosts, because they contain so much dust, they are completely invisible at optical and near-IR wavelengths. Hence, a detailed knowledge of their spectral energy distributions (SED) has been unavailable. To date, therefore, only crude models have been used to estimate the properties of the enveloping dust shells and the embedded clusters. We propose to remedy this situation by obtaining mid- and far-IR photometry with IRAC and MIPS, and mid-IR spectroscopy with IRS, of UDHIIs identified in radio maps of Haro 3 and IC 4662. The photometry and spectroscopy will be combined with the radio data to generate SEDs for the UDHIIs, which will then be fit with dusty radiative transfer models to determine the properties of the dust envelope. In addition, the emission lines expected in the IRS spectra will be used to estimate the extinction, electron density, temperature, abundances, and ionization rates in the embedded HII regions. The results will be used to place additional constraints on the ages and masses of the embedded stellar clusters. The sensitivity provided by the Spitzer Space Telescope will also allow us to search for fainter UDHIIs and construct their luminosity function.
Johnson Kelsey
Vacca William
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