A quasar-galaxy merger at <i>z</i> ∼ 6.2: Black hole mass and quasar properties from the NIRSpec spectrum
F. Loiacono, Roberto Decarli, M. Mignoli, Emanuele Paolo Farina, Eduardo Bañados, Sarah E. I. Bosman, Anna–Christina Eilers, Jan–Torge Schindler, Michael A. Strauss, M. Vestergaard, Feige Wang, Laura Blecha, C. L. Carilli, A. Comastri, Thomas Connor, Tiago Costa, Massimo Dotti, Xiaohui Fan, R. Gilli, Hyunsung D. Jun, Weizhe Liu, Alessandro Lupi, Madeline A. Marshall, Chiara Mazzucchelli, R. A. Meyer, Marcel Neeleman, Roderik Overzier, Antonio Pensabene, Dominik A. Riechers, Benny Trakhtenbrot, Maxime Trebitsch, Bram Venemans, Fabian Walter, Jinyi Yang
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 μm 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 H β line from the broad line region, we obtain an estimate of the black hole mass M BH, H β ∼ 2.7 × 10 9 M ⊙ . This value is within a factor ≲1.5 of the H α -based black hole mass from the same spectrum ( M BH, H α ∼ 1.93 × 10 9 M ⊙ ) and is consistent with a previous estimate relying on the Mg II λ 2799 line ( M BH, MgII ∼ 2.65 × 10 9 M ⊙ ). 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 λ Edd, H β ∼ 0.67 ( λ Edd, H α ∼ 0.96) is in line with the overall quasar population at z ≳ 6. The relative strengths of the [O III ], Fe II , and H β lines are consistent with the empirical “Eigenvector 1” correlations as observed for low redshift quasars. We find evidence for blueshifted [O III ] λ 5007 emission with a velocity offset Δ v [O III] = −1922 ± 39 km s −1 from the systemic velocity and a full width at half maximum (FWHM) FWHM ([O III ]) = 2776 −74 +75 km s −1 . This may be the signature of outflowing gas from the nuclear region, despite the true values of Δ v [O III] and FWHM ([O III ]) likely being more uncertain due to the blending with H β and Fe II lines. Our study demonstrates the unique capabilities of NIRSpec in capturing quasar spectra at cosmic dawn and studying their properties in unprecedented detail.