TY  - JOUR
A1  - Muzahid, S.
A1  - Fonseca, G.
A1  - Roberts, A.
A1  - Rosenwasser, B.
A1  - Richter, Philipp
A1  - Narayanan, A.
A1  - Churchill, C.
A1  - Charlton, J.
T1  - COS-Weak: probing the CGM using analogues of weak Mg II absorbers at z < 0.3
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present a sample of 34 weak metal line absorbers at z < 0.3 selected by the simultaneous >3σ detections of the Si iiλ1260 and C iiλ1334 absorption lines, with Wr(SiII)<0.2 Å and Wr(CII)<0.3 Å, in archival HST/COS spectra. Our sample increases the number of known low-z ‘weak absorbers’ by a factor of >5. The column densities of H i and low-ionization metal lines obtained from Voigt profile fitting are used to build simple photoionization models. The inferred densities and line-of-sight thicknesses of the absorbers are in the ranges of −3.3 < log nH/cm−3 < −2.4 and ∼1 pc–50 kpc (median ≈500 pc), respectively. Most importantly, 85 per cent (50 per cent) of these absorbers show a metallicity of [Si/H]>−1.0(0.0)⁠. The fraction of systems showing near-/supersolar metallicity in our sample is significantly higher than in the H i-selected sample of Wotta et al., and the galaxy-selected sample of Prochaska et al., of absorbers probing the circum-galactic medium at similar redshift. A search for galaxies has revealed a significant galaxy-overdensity around these weak absorbers compared to random positions with a median impact parameter of 166 kpc from the nearest galaxy. Moreover, we find the presence of multiple galaxies in ≈80 per cent of the cases, suggesting group environments. The observed dN/dz of 0.8 ± 0.2 indicates that such metal-enriched, compact, dense structures are ubiquitous in the haloes of low-z group galaxies. We suggest that these are transient structures that are related to galactic outflows and/or stripping of metal-rich gas from galaxies.
KW  - galaxies: formation
KW  - galaxies: haloes
KW  - quasar: absorption line
Y1  - 2018
U6  - https://doi.org/10.1093/mnras/sty529
SN  - 0035-8711
SN  - 1365-2966
VL  - 476
IS  - 4
SP  - 4965
EP  - 4986
PB  - Oxford Univ. Press
CY  - Oxford
ER  -