DUST AND GAS IN THE MAGELLANIC CLOUDS FROM THE HERITAGE HERSCHEL KEY PROJECT. I. DUST PROPERTIES AND INSIGHTS INTO THE ORIGIN OF THE SUBMM EXCESS EMISSION

The dust properties in the Large and Small Magellanic Clouds are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 μm. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a powerlaw emissivity (SMBB), a single temperature blackbody modified by a broken power-law emissivity (BEMBB), and two blackbodies with different temperatures, both modified by the same power-law emissivity (TTMBB). Using these models we investigate the origin of the submm excess; defined as the submillimeter (submm) emission above that expected from SMBB models fit to observations < 200μm. We find that the BEMBB model produces the lowest fit residuals with pixel-averaged 500 μm submm excesses of 27% and 43% for the LMC and SMC, respectively. Adopting gas masses from previous works, the gas-to-dust ratios calculated from our the fitting results shows that the TTMBB fits require significantly more dust than are available even if all the metals present in the interstellar medium (ISM) were condensed into dust. This indicates that the submm excess is more likely to be due to emissivity variations than a second population of colder dust. We derive integrated dust masses of (7.3±1.7)×10 and (8.3±2.1)×10 M for the LMC and SMC, respectively. We find significant correlations between the submm excess and other dust properties; further work is needed to determine the relative contributions of fitting noise and ISM physics to the correlations. Subject headings: infrared: galaxies, infrared: ISM, ISM: general, Magellanic Clouds 1 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA 2 Sterrenkundig Observatorium, Universiteit Gent, Gent, Belgium 3 Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l Université, F-67000 Strasbourg, France 4 Department of Astronomy, 475 North Charter St., University of Wisconsin, Madison, WI 53706, USA 5 CESR, Université de Toulouse, UPS, 9 Avenue du Colonel Roche, F-31028 Toulouse, Cedex 4, France 6 Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse Cedex 4, France 7 Department of Astronomy, Lab for Millimeter-wave Astronomy, University of Maryland, College Park, MD 20742-2421, USA 8 Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 9 Oak Ridge Associated Universities (ORAU), Oak Ridge, TN 37831, USA 10 Louisiana State University, Department of Physics & Astronomy, 233-A Nicholson Hall, Tower Dr., Baton Rouge, LA 70803, USA 11 Steward Observatory, University of Arizona, 933 North Cherry Ave., Tucson, AZ 85721, USA 12 Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756, USA 13 Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan 14 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching-bei-Mnchen, Germany 15 CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, F91191 Gif-sur-Yvette, France 16 Max-Planck-Institut für Astronomie, Königstuhl 17, D69117 Heidelberg, Germany 17 Department of Astronomy, University of Virginia, and National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA 18 Sterrewacht Leiden, Leiden University, P.O. Box 9513, NL2300 RA Leiden, The Netherlands 19 National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo, 181-8588, Japan 20 314 Physics Building, Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA 21 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK 22 Department of Astrophysics, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan 23 CNRS, Observatoire de Paris Lab. GEPI, Bat. 11, 5, place Jules Janssen, 92195 Meudon CEDEX, France 24 Departamento de Astronomı́a, Universidad de Chile, Casilla 36-D, Santiago, Chile 25 The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218, USA 26 Center for Astrophysics and Space Sciences, Department of Physics, University of California, 9500 Gilman Dr, La Jolla, San Diego, CA 92093, USA https://ntrs.nasa. gov/search.jsp? R=20150000803 2019-12-09T17:38:19+00:00Z