The black hole mass of the z=2.805 multiply imaged quasar SDSS J2222+2745 from velocity-resolved time lags of the C iv emission line

Abstract

We present the first results of a 4.5 yr monitoring campaign of the three bright images of multiply imaged z = 2.805 quasar SDSS J2222+2745 using the Gemini North Multi-Object Spectrograph and the Nordic Optical Telescope. We take advantage of gravitational time delays to construct light curves surpassing 6 yr in duration in the observed frame and achieve an average spectroscopic cadence of 10 days during the 8 months of visibility per season. Using multiple secondary calibrators and advanced reduction techniques, we achieve percent-level spectrophotometric precision and carry out an unprecedented reverberation mapping analysis, measuring both integrated and velocity-resolved time lags for the C iv emission line. The full line lags the continuum by Τ(cen)=36.5-3.9+2.9 rest-frame days. We combine our measurement with published C iv emission line lags and derive the r(BLR) - L relationship log10 (Τ/day)=(0.99 +/- 0.07)+(0.48 +/- 0.03)log10 [λLλ(1350AA)/1044erg s-1] with 0.30 +/- 0.06 dex intrinsic scatter. The velocity-resolved lags are consistent with circular Keplerian orbits, with Τ(cen)=86.2-5.0+4.5, 25-15+11 and 7.5-3.5+4.2 rest-frame days for the core, blue wing, and red wing, respectively. Using σline with the mean spectrum and assuming log10(fmean,σ)=0.52 +/- 0.26, we derive log10(MBH/M☉)=8.63 +/- 0.27 . Given the quality of the data, this system represents a unique benchmark for calibration of M-BH estimators at high redshift. Future work will present dynamical modeling of the data to constrain the virial factor f and MBH.