Characterizing circumgalactic gas around massive ellipticals at z ∼ 0.4 – II. Physical properties and elemental abundances

Abstract

We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d < 160 kpc of luminous red galaxies (LRGs). The sample comprises 16 intermediatered-shift (z = 0.21-0.55) LRGs of stellar mass M-star > 10(11 )M(circle dot). Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full H I Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually matched components, we show that cool gas (T similar to 10(4) K) density and metallicity can vary by more than a factor of 10 in an LRG halo. Specifically, metal-poor absorbing components with <1/10 solar metallicity are seen in 50 percent of the LRG haloes, while gas with solar and super-solar metallicity is also common. These results indicate a complex multiphase structure and poor chemical mixing in these quiescent haloes. We calculate the total surface mass density of cool gas, Sigma(cool) by applying the estimated ionization fraction corrections to the observed H column densities. The radial profile of Sigma(cool) is best described by a projected Einasto profile of slope alpha = 1 and scale radius r(s) = 48 kpc. We find that typical LRGs at z similar to 0.4 contain cool gas mass of Sigma(cool) = (1 - 2) x 10(10)M(circle dot) at d < 160 kpc (or as much as Sigma(cool) approximate to 4 x 10(10) M-circle dot at d < 500 kpc), comparable to the cool CGM mass of star-forming galaxies. Furthermore, we show that high-ionization O VI and low-ionization absorption species exhibit distinct velocity profiles, highlighting their different physical origins. We discuss the implications of our findings for the origin and fate of cool gas in LRG haloes.