The properties of 70micron selected high-redshift galaxies in the Extended Groth Strip

TL;DR

This study analyzes the infrared properties of high-redshift, infrared-luminous galaxies in the Extended Groth Strip, revealing heavy dust obscuration and differences from local galaxy counterparts, with implications for understanding galaxy evolution.

Contribution

It provides new equations for estimating total infrared luminosity from MIPS photometry and compares high-redshift galaxy SEDs to local templates, highlighting significant differences.

Findings

Most galaxies are starburst-type with high dust extinction.

Semi-empirical local templates underestimate far-infrared emission.

High-redshift galaxies show a decoupling of mid-infrared slope from other properties.

Abstract

We examine the infrared properties of 43 high redshift (0.1<z<1.2), infrared-luminous galaxies in the Extended Groth Strip (EGS), selected by a deep 70 micron survey with the Multiband Imaging Photometer on Spitzer (MIPS). In addition and with reference to starburst-type Spectral Energy Distributions (SEDs), we derive a set of equations for estimating the total infrared luminosity (L_IR) in the range 8-1000 microns using photometry from at least one MIPS band. 42 out of 43 of our sources' optical/infrared SEDs (lambda_observed < 160 microns) are starburst-type, with only one object displaying a prominent power-law near-infrared continuum. For a quantitative analysis, models of radiation transfer in dusty media are fit onto the infrared photometry, revealing that the majority of galaxies are represented by high extinction, A_v>35 and for a large fraction (~50 per cent) the SED turns over into the Rayleigh-Jeans regime at wavelengths longward of 90 microns. For comparison, we also fit semi-empirical templates based on local galaxy data, however, these underestimate the far-infrared SED shape by a factor of at least 2 and in extreme cases up to 10 for the majority (~70 per cent) of the sources. Further investigation of SED characteristics reveals that the mid-infrared (70/24 microns) continuum slope is decoupled from various galaxy properties such as the total infrared luminosity and far-infrared peak, quantified by the L_160/L_70 ratio. In view of these results, we propose that these high-redshift galaxies have different properties to their local counterparts, in the sense that large amounts of dust cause heavy obscuration and are responsible for an additional cold emissive component, appearing as a far-infrared excess in their SEDs.