Starburst and cirrus models for submillimeter galaxies

TL;DR

This study models submillimeter galaxies using radiative transfer techniques, revealing that some are dominated by cirrus emission while others require combined starburst and cirrus components, with typical luminosities around 10^12.5 solar luminosities.

Contribution

It introduces detailed radiative transfer models for submillimeter galaxies, analyzing the roles of cirrus and starburst emissions in their infrared spectra.

Findings

25% of galaxies are explained by cirrus emission alone.

Most galaxies require combined starburst and cirrus models.

Starburst and cirrus components have comparable luminosities.

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 160mu 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 L=10^12.5 Lo) and cirrus (median L=10^12.4 Lo) components. This could arise if the galaxies have been forming stars continuously for the last 250Myr with the star formation occurring in the last 5Myr being shrouded by high-optical-depth molecular cloud dust, whereas the rest of the starlight is attenuated by diffuse dust or cirrus with an Av of about 1mag.