Multi-wavelength analysis of the dust emission in the Small Magellanic Cloud^*

¹ UMR 7550, Centre de Données Astronomiques de Strasbourg (CDS), Université Louis Pasteur, 67000 Strasbourg, France e-mail: bot@astro.u-strasbg.fr
² Institut d'Astrophysique Spatiale, Université Paris-Sud, 91405 Orsay, France
³ UMS 2201, Observatoire de Paris, 75014 Paris, France

Received: 19 December 2003
Accepted: 28 April 2004

Abstract

We present an analysis of dust grain emission in the diffuse interstellar medium of the Small Magellanic Cloud (SMC). This study is motivated by the availability of 170 m ISOPHOT data covering a large part of the SMC, with a resolution making it possible to disentangle the diffuse medium from the star forming regions. After data reduction and subtraction of Galactic foreground emission, we used the ISOPHOT data together with HiRes IRAS data and ATCA/Parkes combined column density maps to determine dust properties for the diffuse medium. We found a far infrared emissivity per hydrogen atom 30 times lower than the Solar neighborhood value. The modeling of the spectral energy distribution of the dust, taking into account the enhanced interstellar radiation field, gives a similar conclusion for the smallest grains (PAHs and very small grains) emitting at shorter wavelength. Assuming Galactic dust composition in the SMC, this result implies a difference in the gas-to-dust ratio (GDR) 3 times larger than the difference in metallicity. This low depletion of heavy elements in dust could be specific of the diffuse ISM and not apply to all the SMC dust if it results from efficient destruction of dust by supernovae explosions.