Quasars as standard candles. III. Validation of a new sample for cosmological studies

Journal
Date Issued
2020
Author(s)
Lusso, E.
•
Risaliti, G.
•
•
Bargiacchi, G.
•
Benetti, M.
•
•
Capozziello, S.
•
Civano, F.
•
Eggleston, L.
•
Elvis, M.
•
Fabbiano, G.
•
•
•
•
Piedipalumbo, E.
•
•
Signorini, M.
•
Vignali, C.
DOI
Abstract
We present a new catalogue of ˜2400 optically selected quasars with spectroscopic redshifts and X-ray observations from either Chandra or XMM-Newton. The sample can be used to investigate the non-linear relation between the ultraviolet (UV) and X-ray luminosity of quasars as well as to build a Hubble diagram up to a redshift of z ˜ 7.5. We selected sources that are neither reddened by dust in the optical and UV nor obscured by gas in the X-rays, and whose X-ray fluxes are free from flux-limit-related biases. After checking for any possible systematics, we confirm, in agreement with our previous works, that the X-ray to UV relation provides distance estimates matching those from supernovae up to z ˜ 1.5, and its slope shows no redshift evolution up to z ˜ 5. We provide a full description of the methodology for testing cosmological models, further supporting a trend whereby the Hubble diagram of quasars is well reproduced by the standard flat cold dark matter model up to z ˜ 1.5-2, but strong deviations emerge at higher redshifts. Since we have minimised all non-negligible systematic effects and proven the stability of the LX - LUV relation at high redshifts, we conclude that an evolution of the expansion rate of the Universe should be considered as a possible explanation for the observed deviation, rather than some systematic (redshift-dependent) effect associated with high-redshift quasars.

Full Table 3 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A150

Volume
642
Start page
A150
Uri
Url
Issn Identifier
0004-6361
Ads BibCode
2020A&A...642A.150L
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open.access
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