A close look at the black hole masses and hot dusty toruses of the first quasars with MIRI-MRS

Sarah E. I. Bosman, Javier Álvarez-Márquez, Frederick B. Davies, Klaudia Protušová, Joseph F. Hennawi, Jinyi Yang, Benedetta Spina, Luis Colina, Xiaohui Fan, Göran Östlin, Fabian Walter, Feige Wang, Martin Ward, Almudena Alonso Herrero, Aaron J. Barth, Silvia Belladitta, Leindert Boogaard, Karina I. Caputi, Thomas Connor, Dominika Ďurovčíková, Anna-Christina Eilers, Alejandro Crespo Gómez, Jens Hjorth, Hyunsung D. Jun, Danial Langeroodi, Weizhe Liu, Alessandro Lupi, Chiara Mazzucchelli, John P. Pye, Pierluigi Rinaldi, Paul van der Werf, Marta Volonteri

First listed 2025-11-04 | Last updated 2025-11-04

Abstract

The presence of supermassive black holes (SMBHs, $M_\text{BH}\sim10^9 M_\odot$) 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 $7.08\leq z<7.64$. We use three new broad lines to measure updated BH masses, H$α$, Pa$α$ and Pa$β$, finding them to be in the range $(4-15)\cdot10^8 M_\odot$. 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 ($θ=40-60^\circ$) of the tori. These constraints are consistent for the four objects and with expectations from luminous quasars. We estimate a total dust mass $(1-4)\cdot10^6 M_\odot$ 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 $\sim5$ 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 $z<3$.

Short digest

JWST/MIRI-MRS spectra of the four most distant luminous type-1 quasars (J0313−1806, J1342+0928, J1007+2115, J1120+0641; z=7.08–7.64) deliver rest-frame optical/IR broad H-alpha, Pa-alpha, and Pa-beta, yielding consistent virial masses MbH=(4–15)×10^8 Msun that agree with prior Mg II while C IV remains biased. The hydrogen-line ratios depart from case A/B in the same way as at z<3, pointing to similar BLR conditions. A hot-dust torus is unambiguously detected in all four; SKIRTOR fits favor face-on viewing with opening angles 40–60 deg and torus dust masses 1–4×10^6 Msun (0.2–7% of host dust), implying depletion in ~5 Myr at observed accretion rates. Together these results indicate z>7 quasar BH masses and accretion are not fundamentally different from z<3 counterparts, yet are still too large to arise from stellar-remnant seeds if epsilon=0.1.

Key figures to inspect

• Figure 1: Use the full MRS spectra to verify line identifications (H-alpha, Pa-alpha, Pa-beta) and the rising near-IR continuum from hot dust; note Channel 4 is missing for J1342+0928 due to cosmic-ray showers, which explains gaps at the reddest wavelengths.
• Figure 2: Inspect the H-alpha multi-component fits and FWHM—J0313−1806 and J1120+0641 show the broadest components, anchoring the largest virial widths; for J1342+0928, residual CR artifacts limit the decomposition to a single broad component.
• Figure 3: Compare single-epoch MbH across five tracers; H-alpha/Pa-alpha/Pa-beta cluster within the intrinsic scatter and align with Mg II, while C IV remains systematically offset even after blueshift correction—this underpins the paper’s mass-robustness claim.
• Figure 4: Read the Balmer–Paschen flux ratios against Cloudy tracks; the positions away from case A/B and not along an extinction vector argue for BLR density/ionization effects similar to those at z<3, supporting the non-evolving BLR conditions conclusion.