J/A+A/663/L7 Quasars as high-redshift standard candles (Sacchi+, 2022)
Quasars as high-redshift standard candles.
Sacchi A., Risaliti G., Signorini M., Lusso E., Nardini E., Bargiacchi G.,
Bisogni S., Civano F., Elvis M., Fabbiano G., Gilli R., Trefoloni B.,
Vignali C.
<Astron. Astrophys. 663, L7 (2022)>
=2022A&A...663L...7S 2022A&A...663L...7S (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Active gal. nuclei ; Redshifts ; X-ray sources ;
Ultraviolet ; Optical ; Stars, distances
Keywords: galaxies: nuclei - quasars: general - cosmology: observations -
distance scale - X-rays: galaxies
Abstract:
The non-linear relation between the X-ray and ultraviolet (UV)
luminosity in quasars has been used to derive quasar distances and to
build a Hubble diagram at redshifts up to z∼7. This cosmological
application is based on the assumption of independence of the relation
on redshift and luminosity. We want to test the reliability of this
hypothesis by studying the spectroscopic properties of high-redshift
quasars in the X-ray and UV bands. We performed a one-by-one analysis
of a sample of 130 quasars at z>2.5 with high-quality X-ray and UV
spectroscopic observations. We found that not only the X-ray to UV
correlation still holds at these redshifts, but its intrinsic
dispersion is as low as 0.12dex (previous works reached 0.20-0.22
dex). For a sample of quasars at z∼3 with particularly high-quality
observations the dispersion further drops to 0.09dex, a value
entirely accountable for by intrinsic variability and source geometry
effects. The composite spectra of these quasars, in both the X-rays
and the UV, do not show any difference with respect to the average
spectra of quasars at lower redshifts. The absence of any spectral
difference between high- and low-z quasars and the tightness of the
X-ray to UV relation suggests that no evolutionary effects are present
in the relation. Therefore, it can be safely employed to derive quasar
distances. Under this assumption, we obtain a measurement of the
luminosity distance at z∼3 with 15% uncertainty, and in a 4 sigma
tension with the concordance model.
Description:
Properties of the 130 sources composing the final sample. For each
source the quasar name, equatorial coordinates, redshift, X-ray photon
index, UV rest-frame monochromatic flux and luminosity at 2500Å,
X-ray rest-frame monochromatic flux and luminosity at 2keV are given.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
sample.dat 258 130 Properties of the final sample
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Byte-by-byte Description of file: sample.dat
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Bytes Format Units Label Explanations
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1- 26 A26 --- Name Quasar name
28- 37 F10.6 deg RAdeg Right ascension (J2000.0)
39- 47 E9.7 deg DEdeg Declination (J2000.0)
49- 55 F7.5 --- z Redshift
57- 74 F18.16 --- Gx Photon index
77- 95 F19.17 --- e_Gx Lower error on photon index
97-115 F19.17 --- E_Gx Upper error on photon index
117-134 F18.15 [10-7W] logLUV Rest-frame luminosities at 2500 Angstroem (1)
136-154 F19.15 [mW/m2] logFUV Rest-frame fluxes at 2500 Angstroem (2)
156-176 E21.19 [10-7W] e_logLUV Error on rest-frame luminosity at
2500 Angstroem
178-195 F18.15 [10-7W] logLX Rest-frame luminosities at 2keV (1)
197-215 F19.15 [mW/m2] logFX Rest-frame fluxes at 2keV (2)
218-237 F20.18 [10-7W] e_logLX Lower error on rest-frame luminosity at 2keV
239-258 F20.18 [10-7W] E_logLX Upper error on rest-frame luminosity at 2keV
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Note (1): Luminosities are in units of log(erg/s)
Note (2): Fluxes are in units of log(erg/s/cm2)
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Acknowledgements:
Andrea Sacchi,
(End) Patricia Vannier [CDS] 04-Jul-2022