A Complete 16 micron-Selected Galaxy Sample at $z\sim1$: Mid-infrared Spectral Energy Distributions

TL;DR

This study presents a complete 16 micron-selected galaxy sample at redshift 0.8-1.3, analyzing their spectral energy distributions to distinguish star formation and AGN activity, revealing correlations with galaxy properties and the star-forming main sequence.

Contribution

It provides a comprehensive analysis of mid-infrared SEDs for a flux-limited galaxy sample at z~1, identifying the dominant energy sources and their relation to galaxy characteristics.

Findings

Over half the galaxies are star formation dominated.

Approximately one sixth are AGN dominated.

Most galaxies follow the star-forming main sequence at z=1.

Abstract

We describe a complete, flux-density-limited sample of galaxies at redshift $0.8 < z < 1.3$ selected at 16 micron. At the selection wavelength near 8 micron rest, the observed emission comes both from dust heated by intense star formation and from active galactic nuclei (AGNs). Fitting the spectral energy distributions (SEDs) of the sample galaxies to local-galaxy templates reveals that more than half the galaxies have SEDs dominated by star formation. About one sixth of the galaxy SEDs are dominated by an AGN, and nearly all the rest of the SEDs are composite. Comparison with X-ray and far-infrared observations shows that combinations of luminosities at rest-frame 4.5 and 8 micron give good measures of both AGN luminosity and star-formation rate. The sample galaxies mostly follow the established star-forming main sequence for $z=1$ galaxies, but of the galaxies more than 0.5 dex above that main sequence, more than half have AGN-type SEDs. Similarly, the most luminous AGNs tend to have higher star-formation rates than the main sequence value. Galaxies with stellar masses $>$10$^{11}$\,\Msun\ are unlikely to host an AGN. About 1% of the sample galaxies show an SED with dust emission typical of neither star formation nor an AGN.