Quenched Cold Accretion of a Large Scale Metal-Poor Filament due to
  Virial Shocking in the Halo of a Massive z=0.7 Galaxy
  Using HST/COS/STIS and HIRES/Keck high-resolution spectra, we have studied a
remarkable HI absorbing complex at z=0.672 toward the quasar Q1317+277. The HI
absorption has a velocity spread of 1600 km/s, comprises 21 Voigt profile
components, and resides at an impact parameter of D=58 kpc from a bright, high
mass [log(M_vir/M_sun) ~ 13.7] elliptical galaxy that is deduced to have a 6
Gyr old, solar metallicity stellar population. Ionization models suggest the
majority of the structure is cold gas surrounding a shock heated cloud that is
kinematically adjacent to a multi-phase group of clouds with detected CIII, CIV
and OVI absorption, suggestive of a conductive interface near the shock. The
deduced metallicities are consistent with the moderate in situ enrichment
relative to the levels observed in the z ~ 3 Ly-alpha forest. We interpret the
HI complex as a metal-poor filamentary structure being shock heated as it
accretes into the halo of the galaxy. The data support the scenario of an early
formation period (z > 4) in which the galaxy was presumably fed by cold-mode
gas accretion that was later quenched via virial shocking by the hot halo such
that, by intermediate redshift, the cold filamentary accreting gas is
continuing to be disrupted by shock heating. Thus, continued filamentary
accretion is being mixed into the hot halo, indicating that the star formation
of the galaxy will likely remain quenched. To date, the galaxy and the HI
absorption complex provide some of the most compelling observational data
supporting the theoretical picture in which accretion is virial shocked in the
hot coronal halos of high mass galaxies.
