2025/11/04 by Sarah E. I. Bosman, Javier Álvarez-Márquez, Bosman, Sarah E. I. +61
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2511.02902
openalex publication_date 2025/11/04 · openalex created_date 2025/11/07 · openalex updated_date 2026/07/28
The presence of supermassive black holes (SMBHs, MBH∼109 M_\odot) at z>7 remains a puzzle. While their existence appears to require exotic formation or growth processes, it is possible that BH mass estimates are incorrect due to differences from the low-z quasars where BH mass scaling relations are calibrated. In this work, we employ JWST MIRI-MRS spectroscopy to measure the rest-frame optical/IR properties of the four highest-redshift known luminous type-1 quasars at 7.08≤ z<7.64. We use three new broad lines to measure updated BH masses, Hα, Paα and Paβ, finding them to be in the range (4-15)⋅108 M_\odot. Our black hole mass estimates from all tracers agree with each other and with previous, less accurate, ground-based measurements based on MgII. The flux ratios of the H lines deviate from expectations for case A and B recombination in the same way as in z<3 quasars, indicating similar physical conditions in the Broad Line Region. Rest-frame near-IR continuum emission from a hot dusty torus surrounding the accretion disc is unambiguously detected in all four objects. We model the emission with SKIRTOR and constrain the inclination (face-on) and the opening angle (θ=40-60^∘) of the tori. These constraints are consistent for the four objects and with expectations from luminous quasars. We estimate a total dust mass (1-4)⋅106 M_\odot in the tori, corresponding to (0.2-7)% of the total dust in the quasar host galaxies. Given observed accretion rates, these SMBHs will deplete their tori in only ∼5 Myr. Overall, we confirm that z>7 SMBHs in quasars could not have grown from stellar-remnant BHs if the radiative efficiency of accretion is 10%. We also find no evidence that inferred BH masses and accretion processes in z>7 quasars differ significantly from their near-identical counterparts at z<3.