Outflowing atomic and molecular gas at z ~ 0.67 towards 1504 + 377

Abstract

We report the detection of OH 1667-MHz and wide H I 21-cm absorption at z˜ 0.67 towards the red quasar 1504 + 377, with the Green Bank Telescope and the Giant Metrewave Radio Telescope. The H I 21-cm absorption extends over a velocity range of ^~600 km s⁻¹ blueward of the quasar redshift (z= 0.674), with the new OH 1667-MHz absorption component at ^~ −430 km s⁻¹, nearly coincident with earlier detections of millimetre-wave absorption at z~ 0.6715. The atomic and molecular absorption appear to arise from a fast gas outflow from the quasar, with a mass outflow rate M ~ 12M_⊙yr⁻¹and a molecular hydrogen fraction f_H2 = (N_H2/N_HI) ~0.2. The radio structure of 1504 + 377 is consistent with the outflow arising as a result of a jet-cloud interaction, followed by rapid cooling of the cloud material. The observed ratio of HCO⁺ and OH column densities is ^~20 times higher than typical values in Galactic and high-z absorbers. This could arise because of small-scale structure in the outflowing gas on sub-parsec scales, which would also explain the observed variability in the H I 21-cm line.