Characterizing the WISE-selected heavily obscured quasar population with optical spectroscopy from the Southern African Large Telescope

Raphael E. Hviding, Ryan C. Hickox, Kevin N. Hainline, Christopher M. Carroll, Michael A. DiPompeo, Wei Yan, Mackenzie L. Jones

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

We present the results of an optical spectroscopic survey of 46 heavily obscured quasar candidates. Objects are selected using their mid-infrared (mid-IR) colours and magnitudes from the Wide-Field Infrared Survey Explorer (WISE) anzd their optical magnitudes from the Sloan Digital Sky Survey. Candidate Active Galactic Nuclei (AGNs) are selected to have mid-IR colours indicative of quasar activity and lie in a region of mid-IR colour space outside previously published X-ray based selection regions. We obtain optical spectra for our sample using the Robert Stobie Spectrograph on the Southern African Large Telescope. 30 objects (65 per cent) have identifiable emission lines, allowing for the determination of spectroscopic redshifts. Other than one object at z ~ 2.6, candidates have moderate redshifts ranging from z = 0.1 to 0.8 with a median of 0.3. 21 (70 per cent) of our objects with identified redshift (46 per cent of the whole sample) are identified as AGNs through common optical diagnostics. We model the spectral energy distributions of our sample and found that all require a strong AGN component, with an average intrinsic AGN fraction at 8 μm of 0.91. Additionally, the fits require large extinction coefficients with an average E(B - V)AGN = 17.8 (average A(V)AGN = 53.4). By focusing on the area outside traditional mid-IR photometric cuts, we are able to capture and characterize a population of deeply buried quasars that were previously unattainable through X-ray surveys alone.

Original languageEnglish (US)
Pages (from-to)1955-1969
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Volume474
Issue number2
DOIs
StatePublished - Feb 21 2018
Externally publishedYes

Keywords

  • Galaxies: active
  • Galaxies: distances and redshifts
  • Quasars: emission lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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