Stephanie M. LaMassa, Francesca Civano, Marcella Brusa, Daniel Stern, Eilat Glikman, Sarah Gallagher, C. Meg Urry, Sabrina Cales, Nico Cappelluti, Carolin Cardamone, Andrea Comastri, Duncan Farrah, Jenny E. Greene, S. Komossa, Andrea Merloni, Tony Mroczkowski, Priyamvada Natarajan, Gordon Richards, Mara Salvato, Kevin SchawinskiEzequiel Treister

Research output: Contribution to journalArticle

9 Scopus citations


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) - (mid-infrared), hereafter , 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 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 space. We demonstrate that optically normal galaxies hosting X-ray AGNs at redshifts can be recovered with an color cut, while they typically are not selected as AGNs based on their colors. Additionally, different observed X-ray luminosity bins favor different regions in parameter space: moderate-luminosity AGNs (1043 erg erg s-1) tend to have red colors, while the highest-luminosity AGNs ( 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.

Original languageEnglish (US)
Article number88
JournalAstrophysical Journal
Issue number1
StatePublished - Feb 10 2016
Externally publishedYes


  • galaxies: active
  • infrared: galaxies
  • quasars: general
  • quasars: supermassive black holes
  • X-rays: galaxies
  • X-rays: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    LaMassa, S. M., Civano, F., Brusa, M., Stern, D., Glikman, E., Gallagher, S., Urry, C. M., Cales, S., Cappelluti, N., Cardamone, C., Comastri, A., Farrah, D., Greene, J. E., Komossa, S., Merloni, A., Mroczkowski, T., Natarajan, P., Richards, G., Salvato, M., ... Treister, E. (2016). ON R - W1 AS A DIAGNOSTIC to DISCOVER OBSCURED ACTIVE GALACTIC NUCLEI in WIDE-AREA X-RAY SURVEYS. Astrophysical Journal, 818(1), [88]. https://doi.org/10.3847/0004-637X/818/1/88