DEIMOS Observations of WISE-Selected, Optically Obscured AGNs

TL;DR

This study uses WISE mid-IR colors and Keck DEIMOS spectroscopy to identify and analyze optically obscured AGNs, revealing effective selection criteria and the need for targeted, multi-wavelength observations to understand their dust properties.

Contribution

It demonstrates that a W1-W2>0.8 color criterion effectively selects obscured AGNs with higher optical extinction, highlighting the importance of targeted spectroscopy and additional IR data.

Findings

W1-W2>0.8 effectively selects obscured AGNs

Optical extinction correlates with IR properties

Targeted observations are essential for highly obscured AGNs

Abstract

While there are numerous criteria for photometrically identifying active galactic nuclei (AGNs), searches in the optical and UV tend to exclude galaxies that are highly dust obscured. This is problematic for constraining models of AGN evolution and estimating the AGN contribution to the cosmic X-ray and IR backgrounds, as highly obscured objects tend to be underrepresented in large-scale surveys. To address this, we identify potentially obscured AGNs using mid-IR color colors from the Wide-field Infrared Survey Explorer (WISE) catalog. This paper presents the results of optical spectroscopy of obscured AGN candidates using Keck DEIMOS, and their physical properties derived from these spectra. We find that a $W1-W2>0.8$ color criterion effectively selects AGNs with a higher median level of $E(B-V)$ extinction compared to the AGNs found in the SDSS DR7 survey. This optical extinction can be measured using SED modeling or by using $r-W1$ as a measure of optical to IR flux. We find that specific, targeted observations are necessary to find the most highly optically obscured AGNs, and that additional far-IR photometry is necessary to further constrain the dust properties of these AGNs.