Evolution of the X-ray emission of radio-quiet quasars

Brandon C. Kelly, Jill Bechtold, Aneta Siemiginowska, Tom Aldcroft, MaŁgorzata Sobolewska

Research output: Contribution to journalArticle

47 Citations (Scopus)

Abstract

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 languageEnglish (US)
Pages (from-to)116-134
Number of pages19
JournalAstrophysical Journal
Volume657
Issue number1 I
DOIs
StatePublished - Mar 1 2007

Fingerprint

quasars
radio
x rays
erg
accretion
luminosity
loudness
accretion disks
curvature
continuums
photons

Keywords

  • Accretion, accretion disks
  • Quasars: general
  • Ultraviolet: galaxies
  • X-rays: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Kelly, B. C., Bechtold, J., Siemiginowska, A., Aldcroft, T., & Sobolewska, M. (2007). Evolution of the X-ray emission of radio-quiet quasars. Astrophysical Journal, 657(1 I), 116-134. https://doi.org/10.1086/510876

Evolution of the X-ray emission of radio-quiet quasars. / Kelly, Brandon C.; Bechtold, Jill; Siemiginowska, Aneta; Aldcroft, Tom; Sobolewska, MaŁgorzata.

In: Astrophysical Journal, Vol. 657, No. 1 I, 01.03.2007, p. 116-134.

Research output: Contribution to journalArticle

Kelly, BC, Bechtold, J, Siemiginowska, A, Aldcroft, T & Sobolewska, M 2007, 'Evolution of the X-ray emission of radio-quiet quasars', Astrophysical Journal, vol. 657, no. 1 I, pp. 116-134. https://doi.org/10.1086/510876
Kelly BC, Bechtold J, Siemiginowska A, Aldcroft T, Sobolewska M. Evolution of the X-ray emission of radio-quiet quasars. Astrophysical Journal. 2007 Mar 1;657(1 I):116-134. https://doi.org/10.1086/510876
Kelly, Brandon C. ; Bechtold, Jill ; Siemiginowska, Aneta ; Aldcroft, Tom ; Sobolewska, MaŁgorzata. / Evolution of the X-ray emission of radio-quiet quasars. In: Astrophysical Journal. 2007 ; Vol. 657, No. 1 I. pp. 116-134.
@article{8e27afd9befa4c0090dff6d32b870473,
title = "Evolution of the X-ray emission of radio-quiet quasars",
abstract = "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 {\AA}) < 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.",
keywords = "Accretion, accretion disks, Quasars: general, Ultraviolet: galaxies, X-rays: galaxies",
author = "Kelly, {Brandon C.} and Jill Bechtold and Aneta Siemiginowska and Tom Aldcroft and MaŁgorzata Sobolewska",
year = "2007",
month = "3",
day = "1",
doi = "10.1086/510876",
language = "English (US)",
volume = "657",
pages = "116--134",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1 I",

}

TY - JOUR

T1 - Evolution of the X-ray emission of radio-quiet quasars

AU - Kelly, Brandon C.

AU - Bechtold, Jill

AU - Siemiginowska, Aneta

AU - Aldcroft, Tom

AU - Sobolewska, MaŁgorzata

PY - 2007/3/1

Y1 - 2007/3/1

N2 - 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.

AB - 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.

KW - Accretion, accretion disks

KW - Quasars: general

KW - Ultraviolet: galaxies

KW - X-rays: galaxies

UR - http://www.scopus.com/inward/record.url?scp=33947494320&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33947494320&partnerID=8YFLogxK

U2 - 10.1086/510876

DO - 10.1086/510876

M3 - Article

AN - SCOPUS:33947494320

VL - 657

SP - 116

EP - 134

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 I

ER -