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 large grids of ionic column densities generated by the photoionization code Cloudy and a Bayesian model calibration to forward-model broad absorption line quasar spectra. We used SimBAL to analyze the HST 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 total log column density is 22.9 (22.4) [cm^-2] for solar (Z=3Z_\odot) metallicity. The outflow lies 1--3 parsecs from the central engine, consistent with the estimated location of the torus. The mass outflow rate is 17--28 M_\odot 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 indictes a relatively dust-free line of sight. The low accretion rate (0.06 L_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 8 times the accretion rate, the wind is likely integral to the accretion physics of the central engine.