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Description
We present a sample of 34 weak metal line absorbers at z<0.3 selected by the simultaneous >3{sigma} detections of the SiII{lambda}1260 and CII{lambda}1334 absorption lines, with W_r_(SiII)<0.2 {AA} and W_r_(CII)<0.3{AA}, 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 HI 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<logn_H_/cm^-3^<-2.4 and ~1pc-50kpc (median ~=500pc), 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 HI-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.
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