Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Ignas Juodžbalis, Ignas Juodžbalis, , ,
| Summary:
Recent discoveries of faint active galactic nuclei (AGN) at the redshift
frontier have revealed a plethora of broad Halpha emitters with optically red
continua, named Little Red Dots (LRDs), which comprise 15-30% of the high
redshift broad line AGN population. Due to their peculiar spectral properties
and X-ray weakness, modeling LRDs with standard AGN templates has proven
challenging. In particular, the validity of single-epoch virial mass estimates
in determining the black hole (BH) masses of LRDs has been called into
question, with some models claiming that masses might be overestimated by up to
2 orders of magnitude, and other models claiming that LRDs may be entirely
stellar in nature. We report the direct, dynamical BH mass measurement in a
strongly lensed LRD at $z = 7.04$. The combination of lensing with deep
spectroscopic data reveals a rotation curve that is inconsistent with a nuclear
star cluster, yet can be well explained by Keplerian rotation around a point
mass of 50 million Solar masses, consistent with virial BH mass estimates from
the Balmer lines. The Keplerian rotation leaves little room for any stellar
component in a host galaxy, as we conservatively infer $M_rm BH/M_*>2$.
Such a ”naked” black hole, together with its near-pristine environment,
indicates that this LRD is a massive black hole seed caught in its earliest
accretion phase.
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