Abstract
We present JWST/MIRI and JWST/NIRSpec observations of the extremely red quasar SDSS J165202.64+172852.3 at z = 2.94 (dubbed J1652), which is one of the most luminous quasars known to date, driving powerful outflows and hosting a clumpy starburst, in the midst of several interacting companions. We estimate the black hole (BH) mass of the system based on the broad Hα and Hβ lines, as well as the broad Paβ emission in the infrared and Mgii in the UV. We recover a very broad range of mass estimates, with individual constraints ranging between log MBH ∼ 9 and 10.1, which is exacerbated if imposing a uniform BLR geometry at all wavelengths. Several factors may contribute to the large spread: measurement uncertainties (insufficient sensitivity to detect the broadest component of the faint Paschen β line, spectral blending, ambiguities in the broad/narrow component distinction), lack of virial equilibrium (in a system characterised by powerful outflows and a high accretion rate), and uncertainties on the luminosityinferred size of the broad line region, especially given central dust obscuration. We broadly constrain the stellar mass of J1652 via SED fitting, which suggests the host to be extremely massive at ∼ 1012.8±0.5M⊙- falling about 2 dex above the characteristic mass of the Schechter fit to the z = 3 stellar mass function. Notably, J1652’s central black hole might be interpreted as being either undermassive, overmassive, or in line with the BH mass- stellar mass relation, depending on the choice of assumptions. The recovered Eddington ratio varies accordingly, but exceeds 10% in any case. We put our results into context by providing an extensive overview and discussion of recent literature results and their associated assumptions. Our findings provide an important demonstration of the uncertainties inherent in virial black hole mass estimates, which are of particular relevance in the JWST era given the increasing number of studies on rapidly accreting quasars at high redshift.