Exploring quasar evolution with proximate molecular absorbers: Insights from the kinematics of highly ionized nitrogen

We investigate the presence and kinematics of N V absorption proximate to high redshift quasars with both strong H 2 and H I absorption at the quasar redshift. Our spectroscopic observations with X-shooter at the VLT reveal a 70% detection rate of N V (in 9 out of 13 quasars with 2.5 < z < 3.3), remarkably higher than the ∼10% detection rate in intervening damped Lyman- α systems and the ∼30% rate observed within a few thousand km s −1 of the source in the general quasar population. While many N V components lie within the velocity range of the neutral gas, the kinematic profiles of high-ionization species appear decoupled from those of low-ionization species, with the former extending over much larger velocity ranges, particularly toward bluer velocities (up to several thousand km s −1 ). We also observe significant variations in the N V to Si IV ratio, which we attribute to varying ionization conditions, with a clear velocity-dependent trend: blueshifted N V components systematically exhibit higher ionization parameters compared to those near the quasar’s systemic redshift. Furthermore, the most redshifted systems relative to the quasar show no evidence of N V absorption. The results suggest that proximate H 2 absorption systems are in critical stages of quasar evolution, during which the quasar remains embedded in a rich molecular environment. Redshifted systems likely trace infalling gas, potentially associated with mergers, prior to the onset of outflows. Such outflows, as traced by N V , may eventually reach or even carry out neutral and molecular gas. This stage would correspond to proximate H 2 systems located around or blueshifted relative to the quasar’s systemic redshift. Finally, the only case in our sample featuring highly blueshifted neutral gas (−2000 km s −1 ) shows no evidence of an association with the quasar. Our findings highlight the need to account for the ionization state when defining a velocity threshold to distinguish quasar-associated systems from intervening ones.