http://arxiv.org/abs/2212.05862
We present the 0.85-2.5-micron discovery spectrum and multi-epoch photometry of the new high-redshift quasar ULAS J081621.47+213442.6 obtained using the GNIRS spectrograph of the Gemini North and near-infrared wide-field camera of the 4-m UKIRT telescopes. The redshift of ULAS J081621.47+213442.6 measured from the MgII 2799 emission line is z=7.461. The absolute magnitude of the quasar is M1450=-25.33. The black hole mass estimated using the MgII 2799 line and Eddington accretion rate are ~5×10^8Msun and ~0.7. The spectrum of ULAS J081621.47+213442.6 exhibits strong NIII] 1750 emission line of a rest-frame equivalent width of ~12.5 A. The high abundance of nitrogen suggests that ULAS J081621.47+213442.6 may be at the peak of the nitrogen enrichment of the circumnuclear region by the asymptotic giant branch stars, which is expected ~0.25 Gyr after the bulk of star formation. The age of the starburst of ULAS J081621.47+213442.6 implied by the high nitrogen abundance, indicates that the active phase of the black hole growth of the quasar may have lasted only ~0.25 Gyr, favoring a massive initial black hole seed. We also observed the flux variations of the UV continuum of ULAS J081621.47+213442.6 caused by the variation in the line-of-sight absorbing column density on a rest-frame timescale of ~47 d. The estimated hydrogen column density of the gas cloud responsible for this variation is N~10^{23.5} cm^{-2}, consistent with the typical column density of mostly neutral, gravitationally bound clouds of the broad line region of quasars.
E. Koptelova and C. Hwang
Tue, 13 Dec 22
69/105
Comments: 12 pages; 4 figures; 4 tables
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