Mining circumgalactic baryons in the low-redshift universe

• Published in: Monthly notices of the Royal Astronomical Society Vol. 445; no. 2; p. 2061
• Main Authors: Liang, Cameron J, Chen, Hsiao-Wen
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 01.12.2014
• Subjects: Astronomy; Atoms & subatomic particles; Confidence intervals; Covering; Enrichment; Galaxies; Heavy elements; Median; Red shift; Silicon; Stars & galaxies; Symbols; Universe
• DOI: 10.1093/mnras/stu1901
• ISSN: 0035-8711

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.../M...) = 9.7 plus or minus 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 ... 0.176. First, abundant hydrogen gas is observed out to d ... 500 kpc, well beyond the dark matter halo radius R... of individual galaxies, with a mean covering fraction of ...60 per cent. In contrast, no heavy elements are detected at d ... 0.7 R... 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 ... 0.7 R... or gaseous clumps giving rise to the observed absorption lines cannot survive at these large distances. Considering all galaxies at d > R... leads to a strict upper limit for the covering fraction of heavy elements of ...3...per cent (at a 95 per cent confidence level) over d = (1 - 9) R... At d < R..., differential covering fraction between low- and high-ionization gas is observed, suggesting that the CGM becomes progressively more ionized from d < 0.3 R... to larger distances. Comparing CGM absorption observations at low and high redshifts shows that at a fixed fraction of R... the CGM exhibits stronger mean absorption at z = 2.2 than at z ... 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. (ProQuest: ... denotes formulae/symbols omitted.)