The Physical Context of PAH Emission in Galaxies: Metallicity, Radiation, and Environment

Details The Physical Context of PAH Emission in Galaxies: Metallicity, Radiation, and Environment The Physical Context of PAH Emission in Galaxies: Metallicity, Radiation, and Environment

Jun 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20518s&link_type=abstract

Spitzer Proposal ID #20518

Physics

Scientific paper

The PAH emission bands between 3-20 microns are uniquely important for modeling high redshift sources in the deep infrared surveys currently being produced by Spitzer's imaging instruments. Although very little is known about the physical mechanisms of formation, excitation and destruction which govern the behavior of PAH molecules, an important correlation has been very recently uncovered in low-metallicity dwarf starbursts: PAH features seem to vanish at a threshold oxygen abundance near 1/5 solar. Given the many factors known to influence PAH emission, it is very likely that metallicity alone does not govern its strength or presence. Early hints from much smaller and shallower spectral mapping data in the center of nearby galaxies suggest strong variability in the PAH emission spectrum on sub-kpc scales. Our goal is to probe the global mechanisms which govern the appearance and behavior of PAH emission. We propose deep, spatially resolved, low-resolution spectral maps from 5 to 38 microns, arranged in radial strips (approximately 1 x 5-10 arcmin) in three nearby galaxies with steep, well-measured oxygen abundance gradients. These data, when combined with existing IRS spectroscopy of bright HII regions in the target sample, will allow us to probe in detail the strength and structure of PAH emission over a wide range of physical parameters in the ISM, including metallicity, radiation field intensity, and environment (e.g. arm/inter-arm). In addition, we will use the five accessible pure rotational molecular hydrogen lines to test PDR models as a function of metallicity, and track low luminosity HII regions with the available fine structure lines of sulfur and neon. The deep, wide coverage spectral mapping strips produced will be of significant general scientific value, and for the two targets in the SINGS Legacy sample, we will waive the proprietary period to maximize their utilization.

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