A quasar-galaxy merger at z ∼ 6.2: Black hole mass and quasar properties from the NIRSpec spectrum

Abstract

We present JWST/NIRSpec integral field data of the quasar PJ308-21 at $z = 6.2342$. As shown by previous ALMA and HST imaging, the quasar has two companion sources, interacting with the quasar host galaxy. The high-resolution G395H/290LP NIRSpec spectrum covers the $2.87 - 5.27\ m$ wavelength range and shows the rest-frame optical emission of the quasar with exquisite quality (signal-to-noise ratio $ 100 - 400$ per spectral element). Based on the line from the broad line region, we obtain an estimate of the black hole mass BH, H beta odot $. This value is within a factor $ 1.5$ of the -based black hole mass from the same spectrum BH, H alpha odot $) and is consistent with a previous estimate relying on the 2799$ line BH, MgII odot $). All these $M_ BH $ estimates are within the $ 0.5$ dex intrinsic scatter of the adopted mass calibrations. The high Eddington ratio of PJ308-21 $ Edd, H beta Edd, H alpha 0.96$) is in line with the overall quasar population at $z 6$. The relative strengths of the and lines are consistent with the empirical "Eigenvector 1" correlations as observed for low redshift quasars. We find evidence for blueshifted 5007$ emission with a velocity offset $ O\ III from the systemic velocity and a full width at half maximum (FWHM) $ FWHM(Oiii ) = . This may be the signature of outflowing gas from the nuclear region, despite the true values of $ O\ III $ and $ FWHM(Oiii )$ likely being more uncertain due to the blending with and lines. Our study demonstrates the unique capabilities of NIRSpec in capturing quasar spectra at cosmic dawn and studying their properties in unprecedented detail.

Probing the C iv Continuum Size–Luminosity Relation in Active Galactic Nuclei with Photometric Reverberation Mapping

“…To date, the R BLR -L 5100 Å relation has been established using almost 200 active galactic nuclei (AGN) in the Hβ region 6 (see Panda et al 2019b;Shen et al 2024; and references therein) and its extrapolation allows M BH estimation for high-z (z ∼ 6) quasars (e.g., Loiacono et al 2024), albeit with large uncertainty. Attempting to calibrate the R BLR -L relation with quasars at higher z (e.g., z ∼ 2 using the C IV line) is exceptionally time-consuming, requiring campaigns spanning ∼20 yr to detect delays (Lira et al 2018;Grier et al 2019;Hoormann et al 2019;Kaspi et al 2021).…”