Physics
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40457s&link_type=abstract
Spitzer Proposal ID #40457
Physics
Scientific paper
Significant progress has recently been made in measuring the mid-IR luminosity of galaxies over an impressive range of parameter space. An empirical trend of decreasing mid-IR luminosity with decreasing metallicity has now been well established. Further, a `transition metallicity' has been identified where a drastic shift occurs in the relative mid-infrared contributions from hot dust continuum and polycyclic aromatic hydrocarbons (PAHs). However, we have not yet pinpointed the physical processes responsible for this shift. We know that the strength of mid-IR emission is dependent on a galaxy's underlying dust and PAH content, as well as the ability of these components to be individually stimulated into emission, destroyed, and regrown through different physical processes in the ISM. However, the conditions regulating these processes remain highly unconstrained. To place strict constraints on the conditions regulating both hot dust and PAH emission we propose Spitzer/IRS spectral mapping of three nearby star-forming irregular galaxies. We will measure the relative strengths of hot dust and PAH emission with resolution on unprecidented spatial scales (70 pc). Our sample of metal-poor targets are the closest systems in which we can investigate the empirical transition where PAHs go from dominating the mid-IR flux to being completely absent, providing the conditions required to understand the physical processes responsible for this transition. In combination with a comprehensive set of ancillary data, we will compare our spectral maps with highly resolved stellar population data to precisely quantify the effects that radiation field strength and hardness and history of supernova activity have on dust and PAHs.
Cannon John
Gehrz Robert
Jackson Dale
Skillman Evan
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