HYPERION: Broad-band X-ray-to-near-infrared emission of quasars in the first billion years of the Universe

¹ Dipartimento di Matematica e Fisica, Università Roma Tre, Via della Vasca Navale 84, 00146 Roma, Italy
² INAF – Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone, Italy
³ INAF – Osservatorio Astronomico di Trieste, Via G. Tiepolo 11, I-34143 Trieste, Italy
⁴ Dipartimento di Fisica, Sezione di Astronomia, Università di Trieste, Via Tiepolo 11, I-34143 Trieste, Italy
⁵ Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
⁶ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, I-34151 Trieste, Italy
⁷ Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁸ Dipartimento di Fisica e Astronomia ‘Augusto Righi’, Università degli Studi di Bologna, Via P. Gobetti, 93/2, 40129 Bologna, Italy
⁹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti, 93/3, I-40129 Bologna, Italy
¹⁰ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹¹ INFN – National Institute for Nuclear Physics, Via Valerio 2, I-34127 Trieste, Italy
¹² Department of Physics, University of Napoli ‘Federico II’, Via Cinthia 9, 80126 Napoli, Italy
¹³ Millennium Institute of Astrophysics (MAS), Nuncio Monseñor Sotero Sanz 100, Providencia, Santiago, Chile
¹⁴ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
¹⁵ Center for Astrophysics – Harvard & Smithsonian, Cambridge, MA 02138, USA
¹⁶ Steward Observatory, University of Arizona, Tucson, Arizona, USA
¹⁷ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
¹⁸ European Space Agency, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹⁹ DiSAT, Università degli Studi dell’Insubria, Via Valleggio 11, I-22100 Como, Italy
²⁰ INFN – Sezione di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy
²¹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate, Italy
²² Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
²³ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
²⁴ Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
²⁵ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, ESAC Campus, 28692 Villanueva de la Cañada, Spain
²⁶ ASI – Agenzia Spaziale Italiana, Via del Politecnico snc, I-00133 Roma, Italy
²⁷ Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 2, I-00185 Roma, Italy
²⁸ INFN – Sezione Roma1, Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 2, I-00185 Roma, Italy
²⁹ Sapienza School for Advanced Studies, Viale Regina Elena 291, I-00161 Roma, Italy
³⁰ Physics Department, Tor Vergata University of Rome, Via della Ricerca Scientifica 1, 00133 Rome, Italy
³¹ INFN – Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
³² Department of Astronomy, University of Maryland, College Park, MD 20742, USA
³³ University of Ljubljana, Department of Mathematics and Physics, Jadranska ulica 19, SI-1000 Ljubljana, Slovenia
³⁴ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, Via A. Corti 12, 20133 Milano, Italy
³⁵ Institut d’Astrophysique de Paris, Sorbonne Université, CNRS, UMR 7095, 98 Bis bd Arago, 75014 Paris, France

^⋆ Corresponding author; ivano.saccheo@uniroma3.it

Received: 25 May 2024
Accepted: 18 October 2024

Abstract

Aims. We aim to characterize the X-ray-to-optical/near-infrared(NIR) broad-band emission of luminous quasars (QSOs) in the first gigayear (Gyr) of cosmic evolution in order to decipher whether or not they exhibit differences compared to the lower-z QSO population. Our goal is also to provide a reliable and uniform catalog of derivable properties for these objects (from fitting their spectral energy distribution), such as bolometric and monochromatic luminosities, Eddington ratios, dust extinction, and the strength of the hot dust emission.

Methods. We gathered all available photometry –from XMM-Newton proprietary data in X-rays to rest-frame NIR wavelengths– for the 18 QSOs in the HYPERION samples (6.0 ≤ z ≤ 7.5). For sources lacking uniform NIR coverage, we conducted NIR observations in the J, H, and K bands. To increase the statistical robustness of our analysis across the UV-to-NIR region, we add 36 additional sources to our sample from the E-XQR-30 sample with 5.7 ≲ z ≲ 6.6. We characterized the X-ray/UV emission of each QSO using average SEDs from luminous Type 1 sources and calculated bolometric and monochromatic luminosities. Finally, we constructed a mean SED extending from the X-rays to the NIR bands.

Results. We find that the UV-optical emission of these QSOs can be modeled with templates of z ∼ 2 luminous QSOs. We observe that the bolometric luminosities derived while adopting some bolometric corrections at 3000 Å (BC_3000 Å) largely used in the literature are slightly overestimated, by 0.13 dex, as they also include reprocessed IR emission. We estimate a revised value of BC_3000 Å = 3.3, which can be used to derive L_bol in z ≥ 6 QSOs. We provide a subsample of 11 QSOs with rest-frame NIR photometry; these show a broad range of hot dust emission strength, with two sources exhibiting low levels of emission. Despite potential observational biases arising from nonuniform photometric coverage and selection biases, we produce an X-ray-to-NIR mean SED for QSOs at z ≳ 6 that is a good match to templates of lower-redshift, luminous QSOs up to the UV–optical range, with a slightly enhanced contribution from hot dust in the NIR.