UV Quasar Outflow Diagnostics

Feedback from active galactic nuclei (AGN) is widely acknowledged as a primary process regulating
the growth of massive galaxies, though the mechanisms driving this feedback are debated. Prevailing
theories suggest that radio-quiet AGN feedback is driven by radiation pressure acting directly on
the interstellar medium (ISM) via dust or by hot winds entraining the cooler ISM, but the relative
importance of these mechanisms is uncertain. Ratios of highly ionized UV emission lines serve as effective
diagnostics of AGN feedback mechanisms due to their sensitivity to the density structure within ionized
clouds. This study presents the first analysis of far-ultraviolet (FUV) spectra from five low-redshift
galactic-scale outflows in obscured quasars using Hubble’s Cosmic Origins Spectrograph. By comparing
narrow-line region UV emission line ratios to theoretical models with varying importance of the two
driving mechanisms, we find three out of five targets fall within the radiation pressure-dominated regime.
Another target falls between model predictions, but slightly favors the radiation pressure-dominated
regime. The lowest luminosity object in our sample may have a dynamically important hot wind
component, but non-detections prevent a clear conclusion in this case.