Tip of the iceberg: overmassive black holes at 4<z<7 found by JWST are not inconsistent with the local ℳ_ BH-ℳ_⋆ relation

JWST is revealing a new remarkable population of high-redshift (z≳4), low-luminosity Active Galactic Nuclei (AGNs) in deep surveys and detecting the host galaxy stellar light in the most luminous and massive quasars at z∼ 6 for the first time. Latest results claim supermassive black holes (SMBHs) in these systems to be significantly more massive than expected from the local BH mass - stellar mass (ℳ_ BH - ℳ_⋆) relation and that this is not due to sample selection effects. Through detailed statistical modeling, we demonstrate that the coupled effects of selection biases (i.e., finite detection limit and requirements on detecting broad lines) and measurement uncertainties in ℳ_ BH and ℳ_⋆ can in fact largely account for the reported offset and flattening in the observed ℳ_ BH - ℳ_⋆ relation toward the upper envelope of the local relation, even for those at ℳ_ BH < 10^8 M_⊙. We further investigate the possible evolution of the ℳ_ BH - ℳ_⋆ relation at z≳ 4 with careful treatment of observational biases and consideration of the degeneracy between intrinsic evolution and dispersion in this relation. The bias-corrected intrinsic ℳ_ BH - ℳ_⋆ relation in the low-mass regime suggests that there might be a large population of low-mass BHs (log ℳ_ BH≲ 5), possibly originating from lighter seeds, remaining undetected or unidentified even in the deepest JWST surveys. These results have important consequences for JWST studies of BH seeding and the coevolution between SMBHs and their host galaxies at the earliest cosmic times.