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 graphic and a molecular hydrogen fraction graphic. 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.