SHELLQs. Black Hole Mass and Eddington Ratio Distributions of Intermediate-Luminosity Quasars at 6<z<7

Masafusa Onoue, John D. Silverman, Yoshiki Matsuoka, Xuheng Ding, Camryn L. Phillips, Michael A. Strauss, Junya Arita, Takuma Izumi, Mahoshi Sawamura, Nobunari Kashikawa, Irham Andika, Kentaro Aoki, Shunsuke Baba, Anna-Christina Eilers, Seiji Fujimoto, Tomotsugu Goto, Masatoshi Imanishi, Kohei Inayoshi, Kazushi Iwasawa, Knud Jahnke, Yuki Kaneko, Toshihiro Kawaguchi, Kotaro Kohno, Chien-Hsiu Lee, Alessandro Lupi, Tohru Nagao, Dragan Salak, Malte Schramm, Yoshiki Toba, Hideki Umehata, Marta Volonteri, Fabian Walter, Feige Wang, Jinyi Yang

First listed 2026-09-10 | Last updated 2026-09-08

Abstract

We present near-infrared spectroscopy of 21 quasars at 6.07 < z < 6.90 obtained with JWST/NIRSpec and Subaru/MOIRCS. These targets have absolute ultraviolet magnitudes of -25 < M_1450 < -22 and are drawn from a sample of z>6 quasars identified in the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project. These quasars occupy the intermediate-luminosity regime between luminous quasars and the faint high-redshift AGNs uncovered by JWST. We detect broad Balmer emission lines and MgII 2798 with underlying continua from the NIRSpec and MOIRCS targets, respectively. The virial black hole masses of this sample span a wide range of 7.2 < log M_BH/M_sun < 9.4, with Eddington ratios of -1.3 < log L_bol/L_Edd < 0.4. Combining these measurements with our previous mass estimates for other SHELLQs quasars, we construct a sample of 27 quasars with M_BH estimates at 6 < z < 7 and derive the distributions of M_BH and L_bol/L_Edd. When compared with luminosity-matched quasars at z ~ 1.3, we find median offsets of delta log M_BH/M_sun = -0.4 and Delta log L_bol/L_Edd = 0.2 in the high-redshift sample. In addition, 11% of the high-redshift quasars are accreting near or above the Eddington limit. As a systematic check, adopting the Eddington-ratio-dependent calibration of single-epoch M_BH estimates increases the inferred super-Eddington fraction to 22%. These results indicate that a representative population of distant supermassive black holes undergo a rapid accretion phase, although not as extreme as that seen in the most luminous quasar population, consistent with the anti-hierarchical growth scenario of supermassive black holes.

Short digest

Onoue et al. use JWST/NIRSpec broad Balmer-line spectroscopy and Subaru/MOIRCS Mg II measurements to estimate virial black-hole masses and Eddington ratios for 21 intermediate-luminosity SHELLQs quasars at 6.07 < z < 6.90, then combine them with earlier measurements into a 27-object z~6–7 sample. The quasars span 7.2 < log(M_BH/M_sun) < 9.4 and -1.3 < log(L_bol/L_Edd) < 0.4; relative to luminosity-matched z~1.3 SDSS quasars, the high-z population has median black-hole masses lower by 0.4 dex and Eddington ratios higher by 0.2 dex. About 11% are near- or super-Eddington accretors, rising to 22% under an Eddington-ratio-dependent single-epoch mass calibration, supporting rapid but less extreme early SMBH growth than in the most luminous z>6 quasars and bridging those objects to faint JWST AGN.

Key figures to inspect

• Figure 1. Use this sample-definition figure to place the new targets in redshift–M_1450 space: SHELLQs fills the intermediate-luminosity interval between luminous EIGER/ASPIRE quasars and the faint JWST-selected AGN regime motivating the study.
• Figure 7. This is the central empirical check on the Balmer-based mass machinery, comparing host-subtracted 5100 Å luminosities with broad Balmer-line luminosities and identifying two outliers, J0844-0132 and J1146-0005, relevant to the reliability of the adopted line diagnostics.
• Figure 14. This synthesis figure directly shows where the z~6–7 SHELLQs quasars lie in black-hole-mass–luminosity and mass–Eddington-ratio space relative to luminous high-z quasars, faint JWST AGN, and consistently recalibrated SDSS quasars.
• Figure 15. Use this conclusion-driving comparison to see the luminosity-matched distribution shift: the 27 SHELLQs quasars are systematically lower in black-hole mass and higher in Eddington ratio than the Monte Carlo-resampled z~1.3 SDSS population.
• Figure 16. This systematic-test figure shows how an Eddington-ratio-dependent single-epoch mass calibration changes the inferred mass and accretion-rate distributions, underpinning the paper's higher 22% super-Eddington fraction estimate.