HST Morphologies of z~2 Dust Obscured Galaxies I: Power-law Sources

TL;DR

This study uses high-resolution Hubble imaging to analyze the morphologies of z~2 Dust Obscured Galaxies, revealing their extended structures, sizes, and potential evolutionary stages, with implications for understanding galaxy formation.

Contribution

First detailed morphological analysis of z~2 Dust Obscured Galaxies using Hubble imaging, highlighting their sizes, structures, and possible post-merger status.

Findings

Most DOGs are spatially extended and not unresolved AGN-dominated.

DOGs have effective radii of 1-6 kpc, smaller than SMGs but larger than quiescent galaxies.

Morphological measures suggest DOGs are more relaxed than local ULIRGs.

Abstract

We present high spatial resolution optical and near-infrared imaging obtained using the ACS, WFPC2 and NICMOS cameras aboard the Hubble Space Telescope of 31 24um--bright z~2 Dust Obscured Galaxies (DOGs) identified in the Bootes Field of the NOAO Deep Wide-Field Survey. Although this subset of DOGs have mid-IR spectral energy distributions dominated by a power-law component suggestive of an AGN, all but one of the galaxies are spatially extended and not dominated by an unresolved component at rest-frame UV or optical wavelengths. The observed V-H and I-H colors of the extended components are 0.2-3 magnitudes redder than normal star-forming galaxies. All but 1 have axial ratios >0.3, making it unlikely that DOGs are composed of an edge-on star-forming disk. We model the spatially extended component of the surface brightness distributions of the DOGs with a Sersic profile and find effective radii of 1-6 kpc. This sample of DOGs is smaller than most sub-millimeter galaxies (SMGs), but larger than quiescent high-redshift galaxies. Non-parametric measures (Gini and M20) of DOG morphologies suggest that these galaxies are more dynamically relaxed than local ULIRGs. We estimate lower limits to the stellar masses of DOGs based on the rest-frame optical photometry and find that these range from ~10^(9-11) M_sun. If major mergers are the progenitors of DOGs, then these observations suggest that DOGs may represent a post-merger evolutionary stage.