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تسجيل مستخدم جديدEvidence for Late-Time Feedback from the Discovery of Multiphase Gas in a Massive Elliptical at $z=0.4$
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Fakhri S. Zahedy
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We report the first detection of multiphase gas within a quiescent galaxy beyond $zapprox0$. 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 Telescopes 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 $N(mathrm{O VI})/mathrm{cm^{-2}} =15.2pm0.1$ and log $N(mathrm{N V})/mathrm{cm^{-2}} =14.6pm0.1$, among the highest known in external galaxies. Assuming the high-ionization absorption features originate in a transient warm ($Tsim10^5,$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.
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