2013MNRAS.428..563H

Using long-slit optical spectroscopy obtained at the 10.4 m Gran Telescopio Canarias, we have examined the gaseous environment of the radio-loud quasar TXS 1436+157 (z = 2.54), previously known to be associated with a large Lyα nebula and a spatially extended Lyα-absorbing structure. From the Lyα nebula, we measure kinematic properties consistent with infall at a rate of ∼10-100 M☉ yr-1 - more than sufficient to power a quasar at the top of the luminosity function.

The absorbing structure lies outside of the Lyα nebula, at a radius of ≳ 40 kpc from the quasar. Against the bright unresolved continuum and line emission from the quasar, we detect in absorption the Nv λλ1239, 1241, Civ λλ1548, 1551 and Siiv λλ1394, 1403 doublets, with no unambiguous detection of absorption lines from any low-ionization species of metal. The metal column densities, taken together with the Hi column density measurement from the literature, indicate that the absorbing gas is predominantly ionized by the quasar, has a mass of hydrogen of ≳ 1.6x1011 M☉, a gas density of ≤18 cm-3, a line-of-sight thickness of ≥18 pc and a covering factor approaching unity. While this absorbing structure is clearly not composed of pristine gas, it has an extremely low metallicity, with ionization models providing a 3σ limit of 12+log(O/H) ≤ 7.3.

To explain these results, we discuss a scenario involving starburst-driven superbubbles and the creation of infalling filaments of cold gas which fuel/trigger the quasar. We also discuss the possibility of detecting large-scale absorbers such as this in emission when illuminated by a powerful quasar.