Characterizing circumgalactic gas around massive ellipticals at z~0.4
  III. The galactic environment of a chemically-pristine Lyman limit absorber
  This paper presents a study of the galactic environment of a
chemically-pristine (<0.6% solar metallicity) Lyman Limit system (LLS)
discovered along the sightline toward QSO SDSSJ135726.27+043541.4 (zQSO=1.233)
at projected distance d=126 physical kpc (pkpc) from a luminous red galaxy
(LRG) at z=0.33. Combining deep Hubble Space Telescope images, MUSE integral
field spectroscopic data, and wide-field redshift survey data has enabled an
unprecedented, ultra-deep view of the environment around this LRG-LLS pair. A
total of 12 galaxies, including the LRG, are found at d<~400 pkpc and
line-of-sight velocity dv<600 km/s of the LLS, with intrinsic luminosity
ranging from 0.001L* to 2L* and a corresponding stellar mass range of
Mstar=10^{7-11} Msun. All 12 galaxies contribute to a total mass of
Mstar=1.6e11 Msun with ~80% contained in the LRG. The line-of-sight velocity
dispersion of these galaxies is found to be {\sigma}_group=230 km/s with the
center of mass at d_group=118 pkpc and line-of-sight velocity offset of
{\Delta}v_group=181 km/s from the LLS. Three of these are located at d<~100
pkpc from the LLS, and they are all faint with intrinsic luminosity <0.02 L*
and gas phase metallicity of ~10% solar in their interstellar medium. The
disparity in the chemical enrichment level between the LLS and the group
members suggests that the LLS originates in infalling intergalactic medium and
that parts of the intergalactic gas near old and massive galaxies can still
remain chemically pristine through the not too distant past.
