Probing the large and massive CGM of a galaxy at z ~ 0.2 using a pair of
  quasars
  We present analysis of two O VI absorbers at redshift z_{abs} = 0.227,
detected in the spectra of two closely spaced QSO sightlines (Q 0107-025 A and
B), observed with the Cosmic Origins Spectrograph (COS) on board the Hubble
Space Telescope (HST). At the same redshift, presence of a single bright (~ 1.2
L*) galaxy at an impact parameter of ~ 200 kpc (proper) from both the
sightlines was reported by Crighton et al. (2010). Using detailed
photoionization models we show that the high ionization phases of both the O VI
absorbers have similar ionization conditions (e.g. log U ~ -1.1 to -0.9),
chemical enrichment (e.g. log Z ~ -1.4 to -1.0), total hydrogen column density
(e.g. log N_{H} (cm^{-2}) ~ 19.6-19.7) and line of sight thickness (e.g.
l_{los} ~ 600-800 kpc). Therefore we speculate that the O VI absorbers are
tracing different parts of same large scale structure, presumably the
circumgalactic medium (CGM) of the identified galaxy. Using sizes along and
transverse to the line of sight, we estimate the size of the CGM to be R ~ 330
kpc. The baryonic mass associated with this large CGM as traced by O VI
absorption is ~ 1.2x10^{11} M_{sun}. A low ionization phase is detected in one
of the O VI systems with near solar metallicity (log Z = 0.20\pm0.20) and
parsec scale size (l_{los} ~ 6 pc), possibly tracing the neutral phase of a
high velocity cloud (HVC) embedded within the CGM.
