Over half of the far-infrared background light comes from galaxies at z >= 1.2

TL;DR

This study shows that over half of the far-infrared background light originates from galaxies at redshifts greater than 1.2, mainly ultraluminous galaxies at z > 1, based on a new extragalactic survey at multiple wavelengths.

Contribution

It provides the first direct measurement linking the far-infrared background to galaxies at z >= 1.2 using multi-wavelength survey data.

Findings

70% of the far-infrared background is from galaxies at z >= 1.2.

The far-infrared signal at longer wavelengths is dominated by ultraluminous galaxies at z > 1.

All of the far-infrared background can be attributed to individual galaxies.

Abstract

Submillimetre surveys during the past decade have discovered a population of luminous, high-redshift, dusty starburst galaxies. In the redshift range 1 <= z <= 4, these massive submillimetre galaxies go through a phase characterized by optically obscured star formation at rates several hundred times that in the local Universe. Half of the starlight from this highly energetic process is absorbed and thermally re-radiated by clouds of dust at temperatures near 30 K with spectral energy distributions peaking at 100 microns in the rest frame. At 1 <= z <= 4, the peak is redshifted to wavelengths between 200 and 500 microns. The cumulative effect of these galaxies is to yield extragalactic optical and far-infrared backgrounds with approximately equal energy densities. Since the initial detection of the far-infrared background (FIRB), higher-resolution experiments have sought to decompose this integrated radiation into the contributions from individual galaxies. Here we report the results of an extragalactic survey at 250, 350 and 500 microns. Combining our results at 500 microns with those at 24 microns, we determine that all of the FIRB comes from individual galaxies, with galaxies at z >= 1.2 accounting for 70 per cent of it. As expected, at the longest wavelengths the signal is dominated by ultraluminous galaxies at z > 1.