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Arxiv: JWST ERS Program Q3D: The pitfalls of virial BH mass constraints shown in a z = 3 quasar with an ultramassive host Published: 4/22/2024 9:00:00 PM Updated: 4/22/2024 9:00:00 PM

Paper abstract: We present JWST MIRI/NIRSpec observations of the extremely red quasar SDSSJ165202.64+172852.3 at z~3, one of the most luminous quasars known to date,driving powerful outflows and hosting a clumpy starburst, amidst severalinteracting companions. We estimate the black hole (BH) mass of the systembased on the broad H\alpha and H\beta lines, as well as the Pa\betaemission in the IR and MgII in the UV. We recover a very broad range of massestimates, with constraints ranging between log M_{\rm BH}=9 and 10.1, whichis exacerbated if imposing a uniform BLR geometry at all wavelengths. Severalfactors may contribute to the large spread: measurement uncertainties(insufficient sensitivity to detect the broadest component of the faintPa\beta line, spectral blending, ambiguities in the broad/narrow componentdistinction), lack of virial equilibrium (in a system characterised by powerfuloutflows and rapid accretion), and uncertainties on the luminosity-inferredsize of the broad line region, a.o. given central dust obscuration. Weconstrain the stellar mass via SED fitting, suggesting the host to be extremelymassive at 10^{12.8\pm 0.5} M_\odot - ~2 dex above the characteristic mass ofthe Schechter fit to the z=3 stellar mass function. Notably, J1652's central BHmight be interpreted as being either undermassive, overmassive, or in line withthe BH mass-stellar mass relation, depending on the choice of assumptions. Therecovered Eddington ratio varies accordingly, but exceeds 10% in any case. Weput our results into context by providing an extensive overview and discussionof recent literature results and their associated assumptions. Our findingsprovide an important demonstration of the uncertainties inherent in virial BHmass estimates, which are of particular relevance in the JWST era given thegrowing number of studies on rapidly accreting quasars at high redshift.