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 sub(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 (~1.2L[sstarf]) galaxy at an impact parameter of ~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., 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 sub(H)(cm super(-2)) ~ 19.6 - 19.7), and line of sight thickness (e.g., l sub(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 ~1.2 x 10 super(11) M sub([middot in circle]). A low ionization phase is detected in one of the O VI systems with near-solar metallicity (log Z = 0.20 + or - 0.20) and parsec scale size (l sub(los) ~ 6 pc), possibly tracing the neutral phase of a high-velocity cloud embedded within the CGM.