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The Herschel Exploitation of Local Galaxy Andromeda (HELGA). II. Dust and Gas in Andromeda

Smith, M. W. L. and Schulz, B. (2012) The Herschel Exploitation of Local Galaxy Andromeda (HELGA). II. Dust and Gas in Andromeda. Astrophysical Journal, 756 (1). Art. No. 40. ISSN 0004-637X. doi:10.1088/0004-637X/756/1/40.

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We present an analysis of the dust and gas in Andromeda, using Herschel images sampling the entire far-infrared peak. We fit a modified-blackbody model to ~4000 quasi-independent pixels with spatial resolution of ~140 pc and find that a variable dust-emissivity index (β) is required to fit the data. We find no significant long-wavelength excess above this model, suggesting there is no cold dust component. We show that the gas-to-dust ratio varies radially, increasing from ~20 in the center to ~70 in the star-forming ring at 10 kpc, consistent with the metallicity gradient. In the 10 kpc ring the average β is ~1.9, in good agreement with values determined for the Milky Way (MW). However, in contrast to the MW, we find significant radial variations in β, which increases from 1.9 at 10 kpc to ~2.5 at a radius of 3.1 kpc and then decreases to 1.7 in the center. The dust temperature is fairly constant in the 10 kpc ring (ranging from 17 to 20 K), but increases strongly in the bulge to ~30 K. Within 3.1 kpc we find the dust temperature is highly correlated with the 3.6 μm flux, suggesting the general stellar population in the bulge is the dominant source of dust heating there. At larger radii, there is a weak correlation between the star formation rate and dust temperature. We find no evidence for "dark gas" in M31 in contrast to recent results for the MW. Finally, we obtained an estimate of the CO X-factor by minimizing the dispersion in the gas-to-dust ratio, obtaining a value of (1.9 ± 0.4) × 10^(20) cm^(–2) [K km s^(–1)]^(–1).

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Smith, M. W. L.0000-0002-3532-6970
Additional Information:© 2012 American Astronomical Society. Received 2012 April 3; accepted 2012 July 2; published 2012 August 13. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. We thank everyone involved with the Herschel Observatory. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF- IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); and IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT/MCYT (Spain). SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including: the University of Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, University of Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCLMSSL, UKATC, University of Sussex (UK); and Caltech, JPL, NHSC, and the University of Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center and the HIFI, PACS, and SPIRE consortia. G.G. is a postdoctoral researcher of the FWO-Vlaanderen (Belgium). The research leading to these results has received funding from the European Community’s Seventh Framework Programme (/FP7/2007-2013/) under grant agreement No.229517. Facilities: Herschel (PACS and SPIRE), Spitzer (MIPS)
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Deutschland für Luft- und Raumfahrt (DLR) (Germany)UNSPECIFIED
European Community Seventh Framework Programme (FP7/2007-2013)229517
Subject Keywords:galaxies: evolution; galaxies: individual (M31); galaxies: ISM; Local Group
Issue or Number:1
Record Number:CaltechAUTHORS:20121107-102932912
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Official Citation:The Herschel Exploitation of Local Galaxy Andromeda (HELGA). II. Dust and Gas in Andromeda M. W. L. Smith et al. 2012 ApJ 756 40
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35326
Deposited By: Ruth Sustaita
Deposited On:07 Nov 2012 18:59
Last Modified:09 Nov 2021 23:14

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