Using Spitzer to probe the nature of submillimetre galaxies in GOODS-N

TL;DR

This study uses deep Spitzer IR data combined with re-analyzed radio observations to identify and analyze submillimetre galaxies in GOODS-N, revealing their starburst nature and spectral properties, and refining understanding of their infrared luminosities.

Contribution

First comprehensive multi-wavelength analysis of SCUBA galaxies in GOODS-N using Spitzer data, providing insights into their spectral energy distributions and starburst characteristics.

Findings

Average SCUBA galaxy is consistent with ultraluminous starburst models but cooler than local ULIRGs.

Submm flux overestimates IR luminosity when using local ULIRG templates.

Wide range of flux ratios indicates strong mid-IR features at high redshift.

Abstract

How does the submm galaxy population detected by SCUBA fit into galaxy evolution? How do these rare starbursting systems, which contribute significantly to high redshift star-formation, relate to other galaxy populations? Deep radio observations have been most useful for studying these systems, but still leave a significant fraction of the population unidentified. Now with the deep IRAC and MIPS images from the GOODS Spitzer Legacy program and a re-analysis of the deep radio data, we are able to identify counterparts for a large fraction of SCUBA galaxies in GOODS-N. All of these counterparts are detected by Spitzer. Given the vast multi-wavelength data in this field, we can study the spectral energy distributions (SEDs) of these systems and determine what is fueling their intense infrared luminosities. A rest-frame composite optical-to-radio SED for all spectroscopically identified submm sources shows that the average SCUBA galaxy is consistent with models of ultraluminous starburst galaxies, although cooler than those observed locally. Because of this, the submm flux alone consistently overestimates IR when using spectral templates which obey the local ULIRG temperature-luminosity relation. The wide range of 24/850 micron flux ratios as a function of redshift indicates the presence of strong mid-IR features, to be confirmed with deep IRS spectroscopy. The IRAC colours of the submm systems provide useful redshift constraints, since, at these redshifts, IRAC samples the stellar bump. The Spitzer photometry of this large sample of submm galaxies has allowed us to put constraints on many of the outstanding issues in submm astronomy.