JWST Detects Broad Hβ Line in MoM-BL-z10 at z=9.9837, Yielding First Virial SMBH Mass at Cosmic Age 470 Myr
MoM-BL-z10 supplies the first virial SMBH mass measurement at z~10, forcing rapid-growth models to invoke either super-Eddington accretion or heavy seeds. The source's similarity to Little Red Dots extends that population to the earliest epochs and highlights JWST's power to uncover faint AGNs missed by earlier surveys.
The detection rests on a systematic search of public JWST PRISM spectra targeting z≥6 broad-line AGNs. A narrow-plus-broad Gaussian fit to Hβ yields S/N=3.87, supported by [Ne III] λ3870 detection and elevated [Ne III]/[O II] and [O III]/Hβ ratios. Compact NIRCam morphology, red UV-optical slopes, and tentative MIRI F770W flux align the source with the Little Red Dots population previously identified at z~6-8.
This places a 10^7-solar-mass black hole only 470 Myr after the Big Bang, tightening constraints on seed formation channels. Either sustained super-Eddington accretion from a stellar-mass seed or a direct-collapse seed of 10^5-10^6 solar masses is required; the latter would revise models that assume light seeds grow solely via mergers and episodic accretion. The alternative LRD-specific bolometric correction lowers the mass to 2×10^6 solar masses at Eddington ratio unity, illustrating how accretion physics assumptions alter early-universe timelines.
Deeper, higher-resolution NIRSpec observations and ALMA [C II] kinematics will test whether the broad line is virial or outflow-driven and whether the host galaxy shows the expected dynamical mass. Such data arriving within the next two cycles can distinguish between the two mass scenarios and calibrate the high-z AGN luminosity function.
Cai et al.: Higher-S/N NIRSpec grating spectra will detect broad Hα at >5σ within 18 months, confirming the virial mass to 0.3 dex precision.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2610.28735)
- [2]Supporting Source(https://arxiv.org/abs/2305.13344)