The Dust Content of Evolved HII Regions: Spitzer and Herschel Characterization

Details The Dust Content of Evolved HII Regions: Spitzer and Herschel Characterization The Dust Content of Evolved HII Regions: Spitzer and Herschel Characterization

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21944420p&link_type=abstract

American Astronomical Society, AAS Meeting #219, #444.20

Astronomy and Astrophysics

Astronomy

Scientific paper

The recent release of high-resolution radio and NIR data of the Galactic Plane makes it possible, for the first time, to clearly distinguish the actual boundary of an HII region from the surrounding Photo-Dissociation Region (PDR). In this light, we have analyzed a uniform sample of 16 evolved HII regions located in a 20 X 20 field observed as part of the Herschel Hi-Gal survey. By combining MAGPIS 20-cm measurements with IRAC 8μm, MIPS 24μm, PACS (70μm and 160μm) and SPIRE (250μm, 350μm and 500μm) data, we have investigated the relative spatial distribution of the various populations of grains traced by these wavelengths. The analysis reveals that dust is clearly associated with the ionized gas in HII regions. In particular, the ionized gas displays a spatial distribution similar to the 24μm emission, which we tentatively interpret as due to a warm population of Big Grains (BG). At the same, we find evidence that radiation-pressure-driven drift, as proposed by Draine (2011), is the main mechanism at work in HII regions. We have also built the Spectral Energy Distributions (SEDs) for 24μm < λ 160μm appear to trace systematically the cold dust component, for which we estimate an equilibrium temperature of the Big Grains (BGs) in the range 20 - 30 K, while for λ < 70-160μm, the data corroborate the presence of a warm dust component, also due to BGs and surrounded by the cold component, at temperatures of the order of 50 - 90 K.

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