Characterizing the Low-Redshift Intergalactic Medium toward PKS 1302-102

Abstract

We present a detailed analysis of the intergalactic metal-line absorption systems in the archival HST STIS and FUSE ultraviolet spectra of the low-redshift quasar PKS 1302-102 (z_QSO = 0.2784). We supplement the archive data with CLOUDY ionization models and a survey of galaxies in the quasar field. There are 15 strong Lyα absorbers with column densities N_{H I} > 14. Of these, six are associated with at least C III λ977 absorption [log N(C^{+ +}) > 13]; this implies a redshift density dN_{C III}/dz = 36_-9⁺¹³ (68% confidence limits) for the five detections with rest equivalent width W_r > 50 mÅ. Two systems show O VI λλ1031, 1037 absorption in addition to C III [log N(O^{+ 5}) > 14]. One is a partial Lyman limit system ( log N_{H I} = 17) with associated C III, O VI, and Si III λ1206 absorption. There are three tentative O VI systems that do not have C III detected. For one O VI doublet with both lines detected at 3 σ with W_r > 50 mÅ, dN_{O VI}/dz = 7_-4⁺⁹. We also search for O VI doublets without Lyα absorption but identify none. From CLOUDY modeling, these metal-line systems have metallicities spanning the range -4 lesssim [ M/H ] lesssim - 0.3. The two O VI systems with associated C III absorption cannot be single-phase, collisionally ionized media based on the relative abundances of the metals and kinematic arguments. From the galaxy survey, we discover that the absorption systems are in a diverse set of galactic environments. Each metal-line system has at least one galaxy within 500 km s^-1 and 600 h^-1₇₅ kpc with L > 0.1L_*.