Context. A non-linear relation between quasar monochromatic luminosities at 2500 Å and 2 keV holds at all observed redshifts and luminosities, and it has been used to derive quasar distances and to build a Hubble diagram of quasars. The choice of the X-ray and UV indicators has so far been somewhat arbitrary and has typically relied on photometric data. Aims: We aim to determine the X-ray and UV proxies that provide the smallest dispersion of the relation in order to obtain more precise distance estimates and to confirm the reliability of the X-ray-to-UV relation as a distance indicator. Methods: We performed a complete UV spectroscopic analysis of a sample of ∼1800 quasars with SDSS optical spectra and XMM-Newton X-ray serendipitous observations. In the X-rays, we analysed the spectra of all the sample objects at redshift z > 1.9, while we relied on photometric measurements at lower redshifts. As done in previous studies, we analysed the relation in small redshift bins, using fluxes instead of luminosities. Results: We show that the monochromatic fluxes at 1 keV and 2500 Å are, respectively, the best X-ray and UV continuum indicators among those that are typically available. We also find a tight relation between soft X-ray and Mg IIλ2800 Å line fluxes, and a marginal dependence of the X-ray-to-UV relation on the width of the Mg II line. Conclusions: Our analysis suggests that the physical quantities that are more tightly linked to one another are the soft X-ray flux at ∼1 keV and the ionising UV flux blueward of the Lyman limit. However, the `usual' monochromatic fluxes at 2 keV and 2500 Å estimated from photometric data provide an almost as tight X-ray-to-UV relation, and can be used to derive quasar distances. The Hubble diagram obtained using spectroscopic indicators is fully consistent with the one presented in previous papers, based on photometric data.

Quasars as standard candles: IV. Analysis of the X-ray and UV indicators of the disc-corona relation / Signorini M.; Risaliti G.; Lusso E.; Nardini E.; Bargiacchi G.; Sacchi A.; Trefoloni B.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 1432-0746. - ELETTRONICO. - 676:(2023), pp. 0-0. [10.1051/0004-6361/202346104]

Quasars as standard candles: IV. Analysis of the X-ray and UV indicators of the disc-corona relation

Signorini M.;Risaliti G.;Lusso E.;Trefoloni B.
2023

Abstract

Context. A non-linear relation between quasar monochromatic luminosities at 2500 Å and 2 keV holds at all observed redshifts and luminosities, and it has been used to derive quasar distances and to build a Hubble diagram of quasars. The choice of the X-ray and UV indicators has so far been somewhat arbitrary and has typically relied on photometric data. Aims: We aim to determine the X-ray and UV proxies that provide the smallest dispersion of the relation in order to obtain more precise distance estimates and to confirm the reliability of the X-ray-to-UV relation as a distance indicator. Methods: We performed a complete UV spectroscopic analysis of a sample of ∼1800 quasars with SDSS optical spectra and XMM-Newton X-ray serendipitous observations. In the X-rays, we analysed the spectra of all the sample objects at redshift z > 1.9, while we relied on photometric measurements at lower redshifts. As done in previous studies, we analysed the relation in small redshift bins, using fluxes instead of luminosities. Results: We show that the monochromatic fluxes at 1 keV and 2500 Å are, respectively, the best X-ray and UV continuum indicators among those that are typically available. We also find a tight relation between soft X-ray and Mg IIλ2800 Å line fluxes, and a marginal dependence of the X-ray-to-UV relation on the width of the Mg II line. Conclusions: Our analysis suggests that the physical quantities that are more tightly linked to one another are the soft X-ray flux at ∼1 keV and the ionising UV flux blueward of the Lyman limit. However, the `usual' monochromatic fluxes at 2 keV and 2500 Å estimated from photometric data provide an almost as tight X-ray-to-UV relation, and can be used to derive quasar distances. The Hubble diagram obtained using spectroscopic indicators is fully consistent with the one presented in previous papers, based on photometric data.
2023
676
0
0
Signorini M.; Risaliti G.; Lusso E.; Nardini E.; Bargiacchi G.; Sacchi A.; Trefoloni B.
File in questo prodotto:
File Dimensione Formato  
aa46104-23.pdf

accesso aperto

Tipologia: Pdf editoriale (Version of record)
Licenza: Open Access
Dimensione 16.66 MB
Formato Adobe PDF
16.66 MB Adobe PDF

I documenti in FLORE sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/1329820
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 1
  • ???jsp.display-item.citation.isi??? 0
social impact