The z=0.54 LoBAL Quasar SDSS J085053.12+445122.5. I. Spectral Synthesis Analysis Reveals a Massive Outflow

We introduce SimBAL, a novel spectral-synthesis procedure that uses grids of ionic column densities generated by the photoionization code Cloudy and a Bayesian model calibration to forward-model broad absorption-line quasar (BALQ) spectra. We used SimBAL to analyze the Hubble Space Telescope Cosmic Origins Spectrograph (COS) spectrum of the low-redshift BALQ SDSS J085053.12+445122.5. SimBAL analysis yielded velocity-resolved information about the physical conditions of the absorbing gas. We found that the ionization parameter and column density increase, and the covering fraction decreases, as a function of velocity. The log column density is 22.9 (22.4) (cm(-2)) for solar (Z = 3 Z(circle dot)) metallicity. The outflow lies 1-3 pc from the central engine, consistent with the estimated location of the torus. The mass outflow rate is 17-28 M-circle dot yr(-1), the momentum flux is consistent with L-Bol/c, and the ratio of the kinematic to bolometric luminosity is 0.8%-0.9%. The outflow velocity is similar to the escape velocity at the absorber's location, and force multiplier analysis indicates that part of the outflow could originate in resonance-line driving. The location near the torus suggests that dust scattering may play a role in the acceleration, although the lack of reddening in this UV-selected object indicates a relatively dust-free line of sight. The low accretion rate (0.06L(Edd)) and compact outflow suggests that SDSS J0850+4451 might be a quasar past its era of feedback, although since its mass outflow is about eight times the accretion rate, the wind is likely integral to the accretion physics of the central engine.