F. Salvestrini
Quasars as standard candles II
Salvestrini, F.; Risaliti, G.; Bisogni, S.; Lusso, E.; Vignali, C.
Authors
Abstract
A tight non-linear relation between the X-ray and the optical-ultraviolet (UV) emission has been observed in active galactic nuclei (AGN) over a wide range of redshift and several orders of magnitude in luminosity, suggesting the existence of an ubiquitous physical mechanism regulating the energy transfer between the accretion disc and the X-ray emitting corona. Recently, our group developed a method to use this relation in observational cosmology, turning quasars into standardizable candles. This work mainly seeks to investigate the potential evolution of this correction at high redshifts. We thus studied the LX − LUV relation for a sample of quasars in the redshift range 4 < z < 7, adopting the selection criteria proposed in our previous work regarding their spectral properties. The resulting sample consists of 53 type 1 (unobscured) quasars, observed either with Chandra or XMM-Newton, for which we performed a full spectral analysis, determining the rest-frame 2 keV flux density, as well as more general X-ray properties such as the estimate of photon index, and the soft (0.5–2 keV) and hard (2–10 keV) unabsorbed luminosities. We find that the relation shows no evidence for evolution with redshift. The intrinsic dispersion of the LX–LUV for a sample free of systematics/contaminants is of the order of 0.22 dex, which is consistent with previous estimates from our group on quasars at lower redshift.
Citation
Salvestrini, F., Risaliti, G., Bisogni, S., Lusso, E., & Vignali, C. (2019). Quasars as standard candles II. Astronomy & Astrophysics, 631, Article A120. https://doi.org/10.1051/0004-6361/201935491
Journal Article Type | Article |
---|---|
Acceptance Date | Sep 18, 2019 |
Online Publication Date | Nov 5, 2019 |
Publication Date | Nov 30, 2019 |
Deposit Date | Mar 11, 2020 |
Publicly Available Date | Mar 11, 2020 |
Journal | Astronomy and astrophysics. |
Print ISSN | 0004-6361 |
Electronic ISSN | 1432-0746 |
Publisher | EDP Sciences |
Peer Reviewed | Peer Reviewed |
Volume | 631 |
Article Number | A120 |
DOI | https://doi.org/10.1051/0004-6361/201935491 |
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Copyright Statement
Salvestrini, F., Risaliti, G., Bisogni, S., Lusso, E. & Vignali, C. (2019). Quasars as standard candles II. Astronomy & Astrophysics 631: A120, reproduced with permission,© ESO.
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