A Chandra survey of z ≥ 4.5 quasars

Jiang Tao Li, Feige Wang, Jinyi Yang, Joel N. Bregman, Xiaohui Fan, Yuchen Zhang

Research output: Contribution to journalReview articlepeer-review

Abstract

X-ray observations provide a unique probe of the accretion disc corona of supermassive black holes (SMBHs). In this paper, we present a uniform Chandra X-ray data analysis of a sample of 152 z ≥ 4.5 quasars. We firmly detect 46 quasars of this sample in 0.5-2 keV above 3σ and calculate the upper limits of the X-ray flux of the remaining. We also estimate the power-law photon index of the X-ray spectrum of 31 quasars. 24 of our sample quasars are detected in the FIRST or NVSS radio surveys; all of them are radio-loud. We statistically compare the X-ray properties of our z ≥ 4.5 quasars to other X-ray samples of active galactic nuclei (AGNs) at different redshifts. The relation between the rest-frame X-ray luminosity and other quasar parameters, such as the bolometric luminosity, UV luminosity, or SMBH mass, shows large scatters. These large scatters can be attributed to the narrow luminosity range at the highest redshift, the large measurement error based on relatively poor X-ray data, and the inclusion of radio-loud quasars in the sample. The LX-LUV relationship is significantly sublinear. We do not find a significant redshift evolution of the LX-LUV relation, expressed either in the slope of this relation, or the departure of individual AGNs from the best-fitting αOX-LUV relation (ΔαOX). The median value of the X-ray photon index is Γ ≈ 1.79, which does not show redshift evolution from z = 0 to z ∼7. The X-ray and UV properties of the most distant quasars could potentially be used as a standard candle to constrain cosmological models. The large scatter of our sample on the Hubble diagram highlights the importance of future large unbiased deep X-ray and radio surveys in using quasars in cosmological studies.

Original languageEnglish (US)
Pages (from-to)2767-2782
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume504
Issue number2
DOIs
StatePublished - Jun 1 2021

Keywords

  • catalogues
  • distance scale
  • early Universe
  • quasars: general
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint

Dive into the research topics of 'A Chandra survey of z ≥ 4.5 quasars'. Together they form a unique fingerprint.

Cite this