On the nature of the first galaxies selected at 350 microns

TL;DR

This paper investigates the properties of the first galaxies selected at 350 microns, revealing their star-forming nature, redshift distribution, and relation to other infrared-selected galaxy populations, with implications for understanding early galaxy evolution.

Contribution

It provides the first spectral and multi-wavelength analysis of 350-micron-selected galaxies, highlighting their star formation activity and differences from submillimeter galaxy populations.

Findings

Galaxies are IR-luminous at 1<z<3, mainly powered by star formation.

350-micron-selected galaxies have similar dust temperatures to submillimeter galaxies.

Most are not detected at 850 or 1100 microns, indicating different selection biases.

Abstract

[abridged] We present constraints on the nature of the first galaxies selected at 350 microns. The sample includes galaxies discovered in the deepest blank-field survey at 350 microns (in the Bootes Deep Field) and also later serendipitous detections in the Lockman Hole. Spectral energy distribution templates are fit to identified counterparts, and the sample is found to comprise IR-luminous galaxies at 1<z<3 predominantly powered by star formation. The first spectrum of a 350-micron-selected galaxy provides an additional confirmation, showing prominent dust grain features typically associated with star-forming galaxies. Compared to submillimeter galaxies selected at 850 and 1100 microns, galaxies selected at 350 microns have a similar range of far-infrared color temperatures. However, no 350-micron-selected sources are reliably detected at 850 or 1100 microns. Galaxies in our sample with redshifts 1<z<2 show a tight correlation between the far- and mid-infrared flux densities, but galaxies at higher redshifts show a large dispersion in their mid- to far-infrared colors. The 350-micron flux densities (15<S(350)<40 mJy) place these objects near the Herschel/SPIRE 350-micron confusion threshold, with the lower limit on the star formation rate density suggesting the bulk of the 350-micron contribution will come from less luminous infrared sources and normal galaxies.