Evidence for Late-time Feedback from the Discovery of Multiphase Gas in a Massive Elliptical at z = 0.4

We report the first detection of multiphase gas within a quiescent galaxy beyond z ≈ 0. The observations use the brighter image of doubly lensed QSO HE 0047-1756 to probe the interstellar medium (ISM) of the massive ( ${M}_{\mathrm{star}}\approx {10}^{11}\,{M}_{\odot }$ ) elliptical lens galaxy at ${z}_{\mathrm{gal}}=0.408$ . Using Hubble Space Telescope's Cosmic Origins Spectrograph (COS), we obtain a medium-resolution FUV spectrum of the lensed QSO and identify numerous absorption features from H₂ in the lens ISM at projected distance d = 4.6 kpc. The H₂ column density is $\mathrm{log}\,N({{\rm{H}}}_{2})/{\mathrm{cm}}^{-2}={17.8}_{-0.3}^{+0.1}$ with a molecular gas fraction of ${f}_{{{\rm{H}}}_{2}}=2 \% \mbox{--}5 \% $ , roughly consistent with some local quiescent galaxies. The new COS spectrum also reveals kinematically complex absorption features from highly ionized species O VI and N V with column densities log N(O VI) $/{\mathrm{cm}}^{-2}=15.2\pm 0.1$ and log N(N V) $/{\mathrm{cm}}^{-2}=14.6\pm 0.1$ , among the highest known in external galaxies. Assuming the high-ionization absorption features originate in a transient warm (T ∼ 10⁵ K) phase undergoing radiative cooling from a hot halo surrounding the galaxy, we infer a mass accretion rate of $\sim 0.5\mbox{--}1.5\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ . The lack of star formation in the lens suggests that the bulk of this flow is returned to the hot halo, implying a heating rate of $\sim {10}^{48}\,\mathrm{erg}\,{\mathrm{yr}}^{-1}$ . Continuous heating from evolved stellar populations (primarily SNe Ia but also winds from AGB stars) may suffice to prevent a large accumulation of cold gas in the ISM, even in the absence of strong feedback from an active nucleus.