Journal article
The most luminous blue quasars at 3.0 < z < 3.3 II. C IV/X-ray emission and accretion disc physics
Astronomy and astrophysics (Berlin), v 653, pA158
28 Sep 2021
Abstract
We analyse the properties of the high-ionisation C iv lambda 1549 broad emission line in connection with the X-ray emission of 30 bright, optically selected quasars at z similar or equal to 3.0 3.3 with pointed XMM-Newton observations, which were selected to test the suitability of active galactic nuclei as cosmological tools. In our previous work, we found that a large fraction (approximate to 25%) of the quasars in this sample are X-ray under-luminous by factors of >3 10. As absorbing columns of greater than or similar to 10(23) cm(-2) can be safely ruled out, their weakness is most likely intrinsic. Here we explore possible correlations between the UV and X-ray features of these sources to investigate the origin of X-ray weakness with respect to X-ray-normal quasars at similar redshifts. We fit the UV spectra from the Sloan Digital Sky Survey of the quasars in our sample and analyse their C iv properties - for example equivalent width (EW) and line peak velocity (nu(peak)) as a function of the X-ray photon index and 2 10 keV flux. We confirm the statistically significant trends of C iv nu(peak)peak and EW with UV luminosity at 2500 angstrom for both X-ray-weak and X-ray-normal quasars, as well as the correlation between X-ray weakness (parametrised through Delta alpha(ox)) and C iv EW. In contrast to some recent work, we do not observe any clear relation between the 2 10 keV luminosity and nu(peak). We find a statistically significant correlation between the hard X-ray flux and the integrated C iv flux for X-raynormal quasars, which extends across more than three (two) decades in C iv (X-ray) luminosity, whilst X-ray-weak quasars deviate from the main trend by more than 0.5 dex. We argue that X-ray weakness might be interpreted in a starved X-ray corona picture associated with an ongoing disc-wind phase. If the wind is ejected in the vicinity of the black hole, the extreme-UV radiation that reaches the corona will be depleted, depriving the corona of seed photons and generating an X-ray-weak quasar. Nonetheless, at the largest UV luminosities ( >10(47) erg s(-1)) there will still be an ample reservoir of ionising photons that can explain the `excess' C iv emission observed in the X-ray-weak quasars with respect to normal sources of similar X-ray luminosities.
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Details
- Title
- The most luminous blue quasars at 3.0 < z < 3.3 II. C IV/X-ray emission and accretion disc physics
- Creators
- E. Lusso - University of FlorenceE. Nardini - University of FlorenceS. Bisogni - Istituto di Astrofisica Spaziale e Fisica Cosmica di MilanoG. Risaliti - University of FlorenceR. Gilli - National Institute for AstrophysicsG. T. Richards - Drexel UniversityF. Salvestrini - Arcetri Astrophysical ObservatoryC. Vignali - National Institute for AstrophysicsG. Bargiacchi - Scuola Superiore MeridionaleF. Civano - Center for Astrophysics Harvard & SmithsonianM. Elvis - Center for Astrophysics Harvard & SmithsonianG. Fabbiano - Center for Astrophysics Harvard & SmithsonianA. Marconi - University of FlorenceA. Sacchi - University of FlorenceM. Signorini - University of Florence
- Publication Details
- Astronomy and astrophysics (Berlin), v 653, pA158
- Publisher
- Edp Sciences S A
- Number of pages
- 22
- Grant note
- 45780 / Fondazione Cassa di Risparmio Firenze
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Physics
- Web of Science ID
- WOS:000700885900009
- Scopus ID
- 2-s2.0-85116333857
- Other Identifier
- 991019168388304721
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- Collaboration types
- Domestic collaboration
- International collaboration
- Web of Science research areas
- Astronomy & Astrophysics