Article

Dust temperature tracing the ISRF intensity in the Galaxy

http://dx.doi.org/10.1051/0004-6361/201014540 01/2010; DOI: 10.1051/0004-6361/201014540

ABSTRACT New observations with ensuremath Herschelensuremath<?iensuremath> allow accurate measurement of the equilibrium temperature of large dust grains heated by the interstellar radiation field (ISRF), which is critical in deriving dust column density and masses. We present temperature maps derived from the ensuremath Herschelensuremath<?iensuremath> SPIRE and PACS data in two fields along the Galactic plane, obtained as part of the Hi-GAL survey during the ensuremath Herschelensuremath<?iensuremath> science demonstration phase (SDP). We analyze the distribution of the dust temperature spatially, as well as along the two lines-of-sight (LOS) through the Galaxy. The zero-level offsets in the ensuremath Herschelensuremath<?iensuremath> maps were established by comparison with the IRAS and ensuremath Planckensuremath<?iensuremath> data at comparable wavelengths. We derive maps of the dust temperature and optical depth by adjusting a detailed model for dust emission at each pixel. The dust temperature maps show variations in the ISRF intensity and reveal the intricate mixture of the warm dust heated by massive stars and the cold filamentary structures of embedded molecular clouds. The dust optical depth at 250 ensuremath Î?ensuremath<?iensuremath>m is well correlated with the gas column density, but with a significantly higher dust emissivity than in the solar neighborhood. We correlate the optical depth with 3-D cubes of the dust extinction to investigate variations in the ISRF strength and dust abundance along the line of sight through the spiral structure of the Galaxy. We show that the warmest dust along the LOS is located in the spiral arms of the Galaxy, and we quantify their respective IR contribution.

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