Probing the Large and Massive Circumgalactic Medium of a Galaxy at z ~ 0.2 using a Pair of Quasars

Abstract

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 (~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 _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 ~1.2 × 10¹¹ M _⊙. 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 (l _los ~ 6 pc), possibly tracing the neutral phase of a high-velocity cloud embedded within the CGM.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.