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 $z\approx0$. The observations use the brighter image of doubly lensed
QSO HE 0047$-$1756 to probe the ISM of the massive ($M_{\rm star}\approx
10^{11} \mathrm{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 $\mathrm{H_2}$ in the lens ISM at projected distance
$d=4.6$ kpc. The $\mathrm{H_2}$ column density is $\log
N(\mathrm{H_2})/\mathrm{cm^{-2}}=17.8^{+0.1}_{-0.3}$ with a molecular gas
fraction of $f_\mathrm{H_2}=2-5\%$, 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 $N(\mathrm{O VI})/\mathrm{cm^{-2}} =15.2\pm0.1$ and log
$N(\mathrm{N V})/\mathrm{cm^{-2}} =14.6\pm0.1$, among the highest known in
external galaxies. Assuming the high-ionization absorption features originate
in a transient warm ($T\sim10^5\,$K) phase undergoing radiative cooling from a
hot halo surrounding the galaxy, we infer a mass accretion rate of $\sim
0.5-1.5\,\mathrm{M_\odot\,yr^{-1}}$. The lack of star formation in the lens
suggests the bulk of this flow is returned to the hot halo, implying a heating
rate of $\sim10^{48}\,\mathrm{erg\,yr^{-1}}$. 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.
