An ultra-dense fast outflow in a quasar at z = 2.4

We present adaptive optics assisted near-IR integral field spectroscopic observations of a luminous quasar at z = 2.4, previously observed as the first known example at high redshift of large-scale quasar-driven outflow quenching star formation in its host galaxy. The nuclear spectrum shows broad and blueshifted Hβ in absorption, which is tracing outflowing gas with high densities (>108-109 cm−3) and velocities in excess of 10 000 km s−1. The properties of the outflowing clouds (covering factor, density, column density and inferred location) indicate that they likely originate from the broad line region. The energetics of such nuclear regions is consistent with that observed in the large-scale outflow, supporting models in which quasar-driven outflows originate from the nuclear region and are energy conserving. We note that the asymmetric profile of both the Hβ and Hα emission lines is likely due to absorption by the dense outflowing gas along the line of sight. This outflow-induced asymmetry has implications on the estimation of the black hole mass using virial estimators, and warns about such effects for several other quasars characterized by similar line asymmetries. More generally, our findings may suggest a broader revision of the decomposition and interpretation of quasar spectral features, in order to take into account the presence of potential broad blueshifted Balmer absorption lines. Our high spatial resolution data also reveal redshifted nebular emission lines, which could be potentially tracing an inflowing stream.