Determine whether single-epoch spectral black-hole masses are systematically overestimated in the most luminous quasars

Determine whether black-hole mass estimates derived from single-epoch spectra are systematically overestimated, at least for the highest-luminosity quasars.

Background

The paper notes that single-epoch virial estimates depend on empirical broad-line-region size–luminosity relations, which exhibit substantial scatter and may introduce selection biases. A spectroastrometric measurement in a quasar at redshift approximately 4 produced a black-hole mass about an order of magnitude lower than the corresponding single-epoch virial estimate, while preliminary results for other quasars also suggested lower masses.

Possible explanations include broad-line-region outflows or a beamed component in the observed active-galactic-nucleus emission. The authors therefore leave unresolved whether the discrepancy reflects a systematic overestimate in single-epoch spectral masses at the highest luminosities.

References

The question arises: Is it possible that, at least at the highest luminosities, $M_{\rm BH}$ estimates from single--epoch spectra are systematically overestimated?

— Direct measures of black hole masses through cosmic time  (2610.21524 - Decarli et al., 15 Oct 2026) in Section 1, subsection “The need for more accurate M_BH estimates,” bullet “Revising BH scaling relations”