Properties of X-ray-selected broad absorption-line quasars

• Published in: Monthly notices of the Royal Astronomical Society 2008-11, Vol.390 (3), p.1229-1240
• Main Authors: Blustin, A. J., Dwelly, T., Page, M. J., McHardy, I. M., Seymour, N., Kennea, J. A., Loaring, N. S., Mason, K. O., Sekiguchi, K.
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Quasars; quasars: absorption lines; quasars: individual: CXOCDFS J033209.5−274807; quasars: individual: CXOU J014517.1−042503; quasars: individual: CXOU J014546.5−042450; quasars: individual: CXOU J014546.9−043031; quasars: individual: CXOU J014553.9−043726; Ultraviolet radiation; ultraviolet: galaxies; X-ray astronomy
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2008.13825.x

Broad absorption-line quasars (commonly termed BALQSOs) contain the most dramatic examples of active galactic nucleus (AGN) driven winds. The high absorbing columns in these winds, ∼1024cm−2, ensure that BALQSOs are generally X-ray faint. This high X-ray absorption means that almost all BALQSOs have been discovered through optical surveys, and so what little we know about their X-ray properties is derived from very bright optically selected sources. A small number of X-ray-selected BALQSOs (XBALQSOs) have, however, recently been found in deep X-ray survey fields. In this paper we investigate the X-ray and rest-frame ultraviolet (UV) properties of five XBALQSOs for which we have obtained XMM–Newton EPIC X-ray spectra and deep optical imaging and spectroscopy. We find that, although the XBALQSOs have an αox steeper by ∼0.5 than normal QSOs, their median αox is nevertheless flatter by 0.30 than that of a comparable sample of optically selected BALQSOs (OBALQSOs). We rule out the possibility that the higher X-ray to optical flux ratio is due to intrinsic optical extinction. We find that the amount of X-ray and UV absorption due to the wind in XBALQSOs is similar, or perhaps greater than, the corresponding wind absorption in OBALQSOs, so the flatter αox cannot be a result of weaker wind absorption. We conclude that these XBALQSOs have intrinsically higher X-ray to optical flux ratios than the OBALQSO sample with which we compare them.