Starburst and cirrus models for submillimeter galaxies

¹ School of Sciences, European University Cyprus, Diogenes Street, Engomi, 1516 Nicosia, Cyprus e-mail: a.efstathiou@euc.ac.cy
² European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching b. München, Germany

Received: 21 October 2008
Accepted: 20 May 2009

Abstract

We present radiative transfer models for submillimeter galaxies with spectroscopic redshifts and mid-infrared spectroscopy from Spitzer/IRS and analyze available Spitzer/MIPS 24, 70 and 160 μm data. We use two types of starburst models, a cirrus model and a model for the emission of an AGN torus in order to investigate the nature of these objects. We find that for three of the objects (25%) cirrus emission alone can account for the mid-infrared spectrum and the MIPS and submillimeter data. For the remaining objects we find that we need a combination of starburst and cirrus in order to fit simultaneously the multi-wavelength data. We find that the typical submillimeter galaxy has comparable luminosity in the starburst (median ) and cirrus (median ) components. This could arise if the galaxies have been forming stars continuously for the last 250 Myr with the star formation occurring in the last 5 Myr being shrouded by high-optical-depth molecular cloud dust, whereas the rest of the starlight is attenuated by diffuse dust or cirrus with an A_V of about 1 mag.