2015MNRAS.448.3718D

We present a detailed analysis of a H2-bearing metal-rich sub-damped Lymanα system at zabs = 0.10115 towards the radio-loud quasar J0441-4313, at a projected separation of ∼ 7.6 kpc from a star-forming galaxy. The H2, C I and Na I absorption are much stronger in the redder of the two components seen in the Hubble Space Telescope/Cosmic Origins Spectrograph spectrum. The best single-component fit to the strong H2 component gives log N(H2) = 16.61±0.05. However, possible hidden saturation in the medium-resolution spectrum can allow for log N(H2) to be as high as 18.9. The rotational excitation temperature of H2 in this component is 133^+33_-22 K. Photoionization models suggest 30-80 percent of the total N(Hi) is associated with the strong H2 component that has a density ≤ 100/ cm3 and is subject to a radiation field that is ≤ 0.5 times the Galactic mean field. The Very Long Baseline Array 1.4 GHz continuum image of the radio source contains only 27 percent of the arcsecond scale emission. Using a previously published spectrum, no 21-cm absorption is found to be associated with the strong H2 component. This suggests that either the N(Hi)) associated with this component is ≤ 50 percent of the total N(Hi)) or the gas covering factor is ≤ 0.27. This is consistent with the results of the photoionization model that uses ultraviolet radiation due to stars in the associated galaxy. The 21-cm absorption previously reported from the weaker H2 component suggests a spin temperature of ≤ 90 K, at odds with the weakness of H2, C I and Na I absorption in this component. From the inferred physical and chemical conditions, we suggest that the gas may be tracing a recent metal-rich outflow from the host galaxy.