Mining circumgalactic baryons in the low-redshift universe

作者：Liang Cameron J^*; Chen Hsiao Wen

来源：Monthly Notices of the Royal Astronomical Society, 2014, 445(2): 2061-2081.

DOI：10.1093/mnras/stu1901

• survey
• galaxies: dwarf
• galaxies: haloes
• intergalactic medium
• quasars: absorption lines

This paper presents an absorption-line study of the multiphase circumgalactic medium (CGM) based on observations of Ly alpha, C II, C IV, Si II, Si III, and Si IV absorption transitions in the vicinities of 195 galaxies at redshift z < 0.176. The galaxy sample is established based on a cross-comparison between public galaxy and quasi-stellar object (QSO) survey data and is characterized by a median redshift of < z > = 0.041, a median projected distance of < d > = 362 kpc to the sightline of the background QSO, and a median stellar mass of log (M-star/M-circle dot) = 9.7 +/- 1.1. Comparing the absorber features identified in the QSO spectra with known galaxy properties has led to strong constraints for the CGM absorption properties at z less than or similar to 0.176. First, abundant hydrogen gas is observed out to d similar to 500 kpc, well beyond the dark matter halo radius R-h of individual galaxies, with a mean covering fraction of approximate to 60 per cent. In contrast, no heavy elements are detected at d greater than or similar to 0.7 R-h from either low-mass dwarfs or high-mass galaxies. The lack of detected heavy elements in low-and high-ionization states suggests that either there exists a chemical enrichment edge at d greater than or similar to 0.7 R-h or gaseous clumps giving rise to the observed absorption lines cannot survive at these large distances. Considering all galaxies at d R-h leads to a strict upper limit for the covering fraction of heavy elements of approximate to 3 per cent (at a 95 per cent confidence level) over d = (1 - 9) R-h. At d < R-h, differential covering fraction between low-and high-ionization gas is observed, suggesting that the CGM becomes progressively more ionized from d < 0.3 R-h to larger distances. Comparing CGM absorption observations at low and high redshifts shows that at a fixed fraction of R-h the CGM exhibits stronger mean absorption at z = 2.2 than at z similar to 0, and that the distinction is most pronounced in low-ionization species traced by C II and Si II absorption lines. We discuss possible pseudo-evolution of the CGM as a result of misrepresentation of halo radius, and present a brief discussion on the implications of these findings.

• 出版日期2014-12-1