4.6 Article

Chandra observations of red Sloan Digital Sky Survey quasars

期刊

ASTRONOMICAL JOURNAL
卷 132, 期 5, 页码 1977-1988

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IOP PUBLISHING LTD
DOI: 10.1086/507842

关键词

quasars : absorption lines; quasars : general; X-rays : galaxies

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We present short Chandra observations of 12 bright (i < 18) z(em) similar to 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 N-H similar to 10(22) 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.

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