Chandra observations of red Sloan Digital Sky Survey quasars

Patrick B. Hall, S. C. Gallagher, Gordon T. Richards, D. M. Alexander, Scott F. Anderson, Franz Bauer, W. N. Brandt, Donald P. Schneider

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


We present short Chandra observations of 12 bright (i < 18) z em ∼ 1.5 quasars from the Sloan Digital Sky Survey chosen to have significantly redder optical colors than most quasars at the same redshift. Of the five quasars with optical properties most consistent with dust reddening at the quasar redshift, four show indirect evidence of moderate X-ray absorption (inferred NH ∼ 1022 cm-2) with a dust-to-gas ratio <1% of the SMC value. The remaining seven objects show no evidence for even moderate intrinsic X-ray absorption. Thus, while optically red quasars are marginally more likely to show signatures of X-ray absorption than optically selected quasars with normal colors, dust-reddened type 1 active galactic nuclei (as opposed to fully obscured type 2 active galactic nuclei) are unlikely to contribute significantly to the remaining unresolved hard X-ray background. The red quasar population includes objects with intrinsically red continua, as well as objects with dust-reddened continua. Improved sample selection is thus needed to increase our understanding of either subpopulation. To identify dust-reddened quasars likely to exhibit X-ray absorption, some measure of spectral curvature is preferable to simple cuts in observed or relative broadband colors.

Original languageEnglish (US)
Pages (from-to)1977-1988
Number of pages12
JournalAstronomical Journal
Issue number5
StatePublished - Nov 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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