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

Abstract

We report the first detection of multiphase gas within a quiescent galaxy beyond z approximate to 0. The observations use the brighter image of doubly lensed QSO HE 0047-1756 to probe the interstellar medium (ISM) of the massive (M-star approximate to 10(11) M-circle dot) elliptical lens galaxy at z(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 H-2 in the lens ISM at projected distance d = 4.6 kpc. The H-2 column density is log N(H-2)/cm(-2) 17.8(-0.3)(+0.1) with a molecular gas fraction of f(H2) = 2%-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) cm(-2) = 15.2 +/- 0.1 and log N(N V) cm(-2) = 14.6 +/- 0.1, among the highest known in external galaxies. Assuming the high-ionization absorption features originate in a transient warm (T similar to 105 K) phase undergoing radiative cooling from a hot halo surrounding the galaxy, we infer a mass accretion rate of similar to 0.5-1.5 M-circle dot 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 similar to 1048 erg 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.