The composite nature of Dust-Obscured Galaxies (DOGs) at z~2-3 in the COSMOS field: I. A Far-Infrared View

TL;DR

This study investigates the nature of Dust-Obscured Galaxies at redshifts 2-3 in the COSMOS field using Herschel far-infrared data, revealing the varying contributions of star formation and AGN activity to their IR emission.

Contribution

It provides a comprehensive analysis of far-IR properties of DOGs, demonstrating the correlation between IR luminosity and AGN contribution, and distinguishing between star-formation and AGN dominance.

Findings

F_24um-bright DOGs have bluer far-IR/mid-IR colors indicating potential AGN presence.

The AGN contribution increases with rest-frame 8 um luminosity.

Faint DOGs are dominated by star formation, while brighter DOGs have significant AGN activity.

Abstract

Dust-Obscured galaxies (DOGs) are bright 24 um-selected sources with extreme obscuration at optical wavelengths. They are typically characterized by a rising power-law continuum of hot dust (T_D ~ 200-1000K) in the near-IR indicating that their mid-IR luminosity is dominated by an an active galactic nucleus (AGN). DOGs with a fainter 24 um flux display a stellar bump in the near-IR and their mid-IR luminosity appears to be mainly powered by dusty star formation. Alternatively, it may be that the mid-IR emission arising from AGN activity is dominant but the torus is sufficiently opaque to make the near-IR emission from the AGN negligible with respect to the emission from the host component. In an effort to characterize the astrophysical nature of the processes responsible for the IR emission in DOGs, this paper exploits Herschel data (PACS + SPIRE) on a sample of 95 DOGs within the COSMOS field. We derive a wealth of far-IR properties (e.g., total IR luminosities; mid-to-far IR colors; dust temperatures and masses) based on SED fitting. Of particular interest are the 24 um-bright DOGs (F_24um > 1mJy). They present bluer far-IR/mid-IR colors than the rest of the sample, unveiling the potential presence of an AGN. The AGN contribution to the total 8-1000 um flux increases as a function of the rest-frame 8 um-luminosity irrespective of the redshift. This confirms that faint DOGs (L_8 um< 10^12 L_sun) are dominated by star-formation while brighter DOGs show a larger contribution from an AGN.