Evidence for late-time feedback from the discovery of multiphase gas in a massive elliptical at z = 0.4.
ZAHEDY F.S., CHEN H.-W., BOETTCHER E., RAUCH M., DECKER FRENCH K. and ZABLUDOFF A.I.
Abstract (from CDS):
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 (Mstar~1011M☉) elliptical lens galaxy at zgal=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 logN(H2)/cm–2=17.8–0.3+0.1 with a molecular gas fraction of fH2_=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 ∼ 105 K) phase undergoing radiative cooling from a hot halo surrounding the galaxy, we infer a mass accretion rate of ∼0.5–1.5M☉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 ∼1048ergyr–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.