Computer Science
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7546w&link_type=abstract
HST Proposal ID #7546
Computer Science
Hst Proposal Id #7546 Interstellar Matter
Scientific paper
We propose to analyze archival WFPC2 exposures in far-UV and visible filters of star forming regions in M31 and M33 to test photoionization models of the diffuse ionized gas. Diffuse Ionized Gas {DIG, also referred to as the Warm Ionized Medium} is the dominant component of the interstellar medium in ionized form, contributing as much as 30 of the total atomic hydrogen column density in galaxies. Sensitive H Alpha observations of nearby galaxies have shown that the DIG contributes 40+/-10 galaxies, which implies that 40 emitted by OB stars apparently goes into ionizing the DIG rather than discrete HII regions. Where these photons come from is an unsolved issue. Can this large fraction be provided by field OB stars, i.e. OB stars outside traditional HII regions, or are Lyman continuum photons leaking out of HII regions? By studying the massive stellar populations in- and outside of HII regions we will answer this question. Specifically, we will combine our ground-based data on the DIG in nearby galaxies with the HST photometry to study the detailed association between the massive stars and the DIG, determine the average spectral types of massive stars in- and outside HII regions, and determine if field stars can produce enough Lyman continuum photons to ionize the DIG. A large HST database of 21 fields imaged in four filters, including the extremely important FUV filter, is available for this analysis.
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