PROBING THE LARGE AND MASSIVE CIRCUMGALACTIC MEDIUM OF A GALAXY AT z ∼ 0.2 USING A PAIR OF QUASARS

We present an analysis of two O-VI absorbers at redshift z(abs) = 0.227, which were detected in the spectra of two closely spaced QSO sightlines (Q 0107-025A and B) and observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope. At the same redshift, the presence of a single bright (similar to 1.2L (*)) galaxy at an impact parameter of similar to 200 kpc (proper) from both the sightlines was reported by Crighton et al. Using detailed photoionization models, we show that the high ionization phases of both the O-VI absorbers have similar ionization conditions (e. g., logU similar to -1.1 to -0.9), chemical enrichment (e. g., log Z similar to -1.4 to -1.0), total hydrogen column density (e. g., logN(H)(cm(-2)) similar to 19.6 -19.7), and line of sight thickness (e. g., l(los) similar to 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 similar to 330 kpc. The baryonic mass associated with this large CGM as traced by O-VI absorption is similar to 1.2 x 10(11)M(circle dot) . A low ionization phase is detected in one of the O-VI systems with near-solar metallicity (log Z = 0.20 +/- 0.20) and parsec scale size (llos similar to 6 pc), possibly tracing the neutral phase of a high-velocity cloud embedded within the CGM.