On R-W1 as A Diagnostic to Discover Obscured Active Galactic Nuclei in Wide-area X-Ray Surveys
Journal
Date Issued
2016
Author(s)
LaMassa, Stephanie M.
•
Civano, Francesca
•
Brusa, Marcella
•
Stern, Daniel
•
Glikman, Eilat
•
Gallagher, Sarah
•
Urry, C. Meg
•
Cales, Sabrina
•
CAPPELLUTI, Nico
•
Cardamone, Carolin
•
•
Farrah, Duncan
•
Greene, Jenny E.
•
Komossa, S.
•
Merloni, Andrea
•
Mroczkowski, Tony
•
Natarajan, Priyamvada
•
Richards, Gordon
•
Salvato, Mara
•
Schawinski, Kevin
•
Treister, Ezequiel
Abstract
Capitalizing on the all-sky coverage of WISE and the 35% and 50% sky coverage from Sloan Digital Sky Survey and Pan-STARRS, respectively, we explore the efficacy of mR (optical) - {m}3.4μ {{m}} (mid-infrared), hereafter R-W1, as a color diagnostic to identify obscured supermassive black hole accretion in wide-area X-ray surveys. We use the ∼16.5 deg2 Stripe 82 X-ray survey data as a test bed to compare R-W1 with R - K, an oft-used obscured active galactic nucleus (AGN) selection criterion, and examine where different classes of objects lie in this parameter space. Most stars follow a well-defined path in R - K versus R-W1 space. We demonstrate that optically normal galaxies hosting X-ray AGNs at redshifts 0.5\lt z\lt 1 can be recovered with an R-W1\gt 4 color cut, while they typically are not selected as AGNs based on their W1-W2 colors. Additionally, different observed X-ray luminosity bins favor different regions in R-W1 parameter space: moderate-luminosity AGNs (1043 erg {{{s}}}-1\lt {L}0.5-10{keV}\lt {10}44 erg s-1) tend to have red colors, while the highest-luminosity AGNs ({L}0.5-10{keV}\gt {10}45 erg s-1) have bluer colors; higher spectroscopic completeness of the Stripe 82X sample is needed to determine whether this is a selection effect or an intrinsic property. Finally, we parameterize X-ray obscuration of Stripe 82X AGNs by calculating their hardness ratios (HRs) and find no clear trends between HR and optical reddening. Our results will help inform best-effort practices in following up obscured AGN candidates in current and future wide-area, shallow X-ray surveys, including the all-sky eROSITA mission.
Volume
818
Issue
1
Start page
88
Issn Identifier
0004-637X
Ads BibCode
2016ApJ...818...88L
Rights
open.access
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