We report new Chandra observations of seven optically faint, z ∼ 4 radio-quiet quasars (RQQs). We have combined these new observations with previous Chandra observations of RQQs to create a sample of 174 sources. These sources have 0.1 < z < 4.7, and 1044 ergs s-1 < νLν (2500 Å) < 1048 ergs s-1. The X-ray detection fraction is 90%. We find that the X-ray loudness of RQQs decreases with UV luminosity and increases with redshift. The model that is best supported by the data has a linear dependence of optical to X-ray ratio αox on cosmic time and a quadratic dependence of αox on log LUV, where αox becomes X-ray quiet more rapidly at higher log LUV. We find no significant evidence for a relationship between the X-ray photon index Fx and the UV luminosity, and we find marginally significant evidence that the X-ray continuum flattens with increasing z (2 σ). The Τx-z anticorrelation may be the result of X-ray spectral curvature, redshifting of a Compton reflection component into the observed Chandra band, and/or redshifting of a soft excess out of the observed Chandra band. Using the results for Τx, we show that the αox-z relationship is unlikely to be a spurious result caused by redshifting of the observable X-ray spectral region. A correlation between αox and z implies evolution of the accretion process. We present a qualitative comparison of these new results with models for accretion disk emission.
|Original language||English (US)|
|Number of pages||19|
|Issue number||1 I|
|State||Published - Mar 1 2007|
- Accretion, accretion disks
- Quasars: general
- Ultraviolet: galaxies
- X-rays: galaxies
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science
FingerprintDive into the research topics of 'Evolution of the X-ray emission of radio-quiet quasars'. Together they form a unique fingerprint.
X-ray and UV parameters of radio-quiet quasars
Kelly, B. C. (Creator) & Bechtold, J. (Creator), Centre de Donnees Strasbourg (CDS), 2009
DOI: 10.26093/cds/vizier.16570116, https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/657/116