http://arxiv.org/abs/1402.3602
(Abridged) This paper presents an absorption-line study of the multiphase circumgalactic medium (CGM) based on observations of a suite of absorption features including Lya, CII, CIV, SiII, SiIII, and SiIV transitions. Cross-matching between public galaxy and QSO survey data has yielded 111 independent galaxy and QSO pairs for which high-quality archival UV spectra of the QSOs and multi-wavelength observations of the galaxies are available. The galaxy sample is characterized by a median redshift of <z> = 0.0232, a median projected distance of <d> = 342 kpc, and a median stellar mass of log (Mstar/Msun) = 9.04\pm 0.93. It is therefore dominated by low-mass dwarf galaxies. Comparing the absorber features identified in the QSO spectra with galaxy properties has led to strong constraints for the CGM at z<~0.06. While abundant hydrogen gas is found beyond the dark matter halo radius Rh and all through d~500 kpc with a mean covering fraction of ~50%, no heavy elements are detected at d>~0.5 Rh. The lack of heavy elements at large distances is unlikely due to ionization effects, since it persists through all ionization states included in the study. Considering all galaxies at d>Rh leads to a strict upper limit for the covering fraction of heavy elements of ~4% (at a 95% confidence level) over d=(1-10) Rh. At d<0.5 Rh, differential covering fraction between low- and high-ionization gas is observed, suggesting that the CGM becomes progressively more ionized from d<0.2 Rh to larger distances. Comparing absorption-line observations of the CGM at low and high redshifts shows that massive starburst galaxies at z=2.2 exhibit significantly stronger mean absorption than dwarf galaxies at z~0 and the distinction is most pronounced in low-ionization species traced by CII and SiII absorption lines, suggesting distinct ionization conditions between the CGM at low and high redshifts.
C. Liang and H. Chen
Tue, 18 Feb 14
19/72
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