HST Detection of Extended Neutral Hydrogen in a Massive Elliptical at z
  = 0.4
  We report the first detection of extended neutral hydrogen (HI) gas in the
interstellar medium (ISM) of a massive elliptical galaxy beyond z~0. The
observations utilize the doubly lensed images of QSO HE 0047-1756 at z_QSO =
1.676 as absorption-line probes of the ISM in the massive (M_star ~ 10^11
M_sun) elliptical lens at z = 0.408, detecting gas at projected distances of d
= 3.3 and 4.6 kpc on opposite sides of the lens. Using the Space Telescope
Imaging Spectrograph (STIS), we obtain UV absorption spectra of the lensed QSO
and identify a prominent flux discontinuity and associated absorption features
matching the Lyman series transitions at z = 0.408 in both sightlines. The HI
column density is log N(HI) = 19.6-19.7 at both locations across the lens,
comparable to what is seen in 21 cm images of nearby ellipticals. The HI gas
kinematics are well-matched with the kinematics of the FeII absorption complex
revealed in ground-based echelle data, displaying a large velocity shear of 360
km/s across the galaxy. We estimate an ISM Fe abundance of 0.3-0.4 solar at
both locations. Including likely dust depletions increases the estimated Fe
abundances to solar or supersolar, similar to those of the hot ISM and stars of
nearby ellipticals. Assuming 100% covering fraction of this Fe-enriched gas,we
infer a total Fe mass of M_cool(Fe)~(5-8)x10^4 M_sun in the cool ISM of the
massive elliptical lens, which is no more than 5% of the total Fe mass observed
in the hot ISM.
