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HYPerluminous quasars at the Epoch of ReionizatION (HYPERION): A new regime for the X-ray nuclear properties of the first quasars

Zappacosta, L.; Piconcelli, E.; Fiore, F.; Saccheo, I.; Valiante, R.; Vignali, C.; Vito, F.; Volonteri, M.; Bischetti, M.; Comastri, A.; Done, C.; Elvis, M.; Giallongo, E.; La Franca, F.; Lanzuisi, G.; Laurenti, M.; Miniutti, G.; Bongiorno, A.; Brusa, M.; Civano, F.; Carniani, S.; D’Odorico, V.; Feruglio, C.; Gallerani, S.; Gilli, R.; Grazian, A.; Guainazzi, M.; Marinucci, A.; Menci, N.; Middei, R.; Nicastro, F.; Puccetti, S.; Tombesi, F.; Tortosa, A.; Testa, V.; Vietri, G.; Cristiani, S.; Haardt, F.; Maiolino, R.; Schneider, R.; Tripodi, R.; Vallini, L.; Vanzella, E.

HYPerluminous quasars at the Epoch of ReionizatION (HYPERION): A new regime for the X-ray nuclear properties of the first quasars Thumbnail


Authors

L. Zappacosta

E. Piconcelli

F. Fiore

I. Saccheo

R. Valiante

C. Vignali

F. Vito

M. Volonteri

M. Bischetti

A. Comastri

M. Elvis

E. Giallongo

F. La Franca

G. Lanzuisi

M. Laurenti

G. Miniutti

A. Bongiorno

M. Brusa

F. Civano

S. Carniani

V. D’Odorico

C. Feruglio

S. Gallerani

R. Gilli

A. Grazian

M. Guainazzi

A. Marinucci

N. Menci

R. Middei

F. Nicastro

S. Puccetti

F. Tombesi

A. Tortosa

V. Testa

G. Vietri

S. Cristiani

F. Haardt

R. Maiolino

R. Schneider

R. Tripodi

L. Vallini

E. Vanzella



Abstract

The existence of luminous quasars (QSOs) at the epoch of reionization (EoR; i.e., z > 6) powered by well-grown supermassive black holes (SMBHs) with masses ≳109 M⊙ challenges models of early SMBH formation and growth. To shed light on the nature of these sources, we started a multiwavelength program based on a sample of 18 HYPerluminous quasars at the Epoch of ReionizatION (HYPERION). These are the luminous QSOs whose SMBHs must have had the most rapid mass growth during the first gigayear of the Universe and therefore acquired the largest mass at their respective epochs. In this paper, we present the HYPERION sample and report results from the first year of the planned three years of observations of the 2.4 Ms XMM-Newton Multi-Year Heritage program on which HYPERION is based. The goal of this program is to accurately characterise the X-ray nuclear properties of QSOs at the EoR. Through a joint X-ray spectral analysis of ten sources, covering the rest-frame ∼2 − 50 keV energy range, we report a steep average photon index (Γ ≈ 2.4 ± 0.1). No absorption is required at levels of 1021 − 1022 cm−2. The measured average Γ is inconsistent at ≥4σ level with the canonical value (Γ = 1.8 − 2) measured in QSOs at z < 6. Such a steep spectral slope is also significantly steeper than that reported in lower-z analog QSOs with similar luminosity or accretion rate, suggesting genuine redshift evolution. Alternatively, we can interpret this result as suggesting the presence of a very low energy cutoff Ecut ≈ 20 keV on a standard Γ = 1.9 power-law, the likes of which is rarely reported at lower z. We also report mild indications that, on average, HYPERION QSOs show higher levels of coronal soft X-rays at 2 keV compared to the accretion disk UV at 2500 Å than expected for lower-z AGN in the high-luminosity regime. We speculate that either a redshift-dependent coupling between the X-ray corona and accretion disk or intrinsically different coronal properties account for the steepness of the X-ray spectral slope, especially in the presence of powerful winds. The reported steep slopes, if confirmed in lower-luminosity regimes, may have an important impact on the design of next-generation X-ray facilities and future surveys designed to investigate the early Universe.

Citation

Zappacosta, L., Piconcelli, E., Fiore, F., Saccheo, I., Valiante, R., Vignali, C., …Vanzella, E. (2023). HYPerluminous quasars at the Epoch of ReionizatION (HYPERION): A new regime for the X-ray nuclear properties of the first quasars. Astronomy & Astrophysics, 678, Article A201. https://doi.org/10.1051/0004-6361/202346795

Journal Article Type Article
Acceptance Date Jul 5, 2023
Online Publication Date Oct 24, 2023
Publication Date 2023-10
Deposit Date Jan 22, 2024
Publicly Available Date Jan 22, 2024
Journal Astronomy & Astrophysics
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 678
Article Number A201
DOI https://doi.org/10.1051/0004-6361/202346795
Keywords Space and Planetary Science; Astronomy and Astrophysics
Public URL https://durham-repository.worktribe.com/output/2160904

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