A compact, metal-rich, kpc-scale outflow in FBQS J0209-0438 : detailed diagnostics from HST/COS extreme UV observations
Faculty of Sciences. Physics
Monthly notices of the Royal Astronomical Society. - Oxford
, p. 3317-3340
University of Antwerp
We present HST/COS observations of highly ionized absorption lines associated with a radio-loud quasar (QSO) at z = 1.1319. The absorption system has multiple velocity components, with an overall width of approximate to 600 km s(-1), tracing gas that is largely outflowing from the QSO at velocities of a few 100 km s(-1). There is an unprecedented range in ionization, with detections of HI, NIII, NIV, NV, OIV, OIV*, OV, OVI, NeVIII, MgX, SV and Ar VIII. We estimate the total hydrogen number density from the column density ratio N(O IV*)/N(O IV) to be log(n(H)/cm(-3)) similar to 3. Combined with constraints on the ionization parameter in the OIV bearing gas from photoionization equilibrium models, we derive a distance to the absorbing complex of 2.3 less than or similar to R less than or similar to 6.0 kpc from the centre of the QSO. A range in ionization parameter, covering similar to two orders of magnitude, suggest absorption path lengths in the range 10(-4.5) less than or similar to l(abs) less than or similar to 1pc. In addition, the absorbing gas only partially covers the background emission from the QSO continuum, which suggests clouds with transverse sizes l(trans) less than or similar to 10(-2.5) pc. Widely differing absorption path lengths, combined with covering fractions less than unity across all ions pose a challenge to models involving simple cloud geometries in associated absorption systems. These issues may be mitigated by the presence of non-equilibrium effects, which can be important in small, dynamically unstable clouds, together with the possibility of multiple gas temperatures. The dynamics and expected lifetimes of the gas clouds suggest that they do not originate from close to the active galactic nuclei, but are instead formed close to their observed location. Their inferred distance, outflow velocities and gas densities are broadly consistent with scenarios involving gas entrainment or condensations in winds driven by either supernovae, or the supermassive black hole accretion disc. In the case of the latter, the present data most likely does not trace the bulk of the outflow by mass, which could instead manifest itself as an accompanying warm absorber, detectable in X-rays.