{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/cos-weak-probing-the-cgm-using-analogs-of","title":"COS-Weak: Probing the CGM using analogs of weak Mg II absorbers at z < 0.3","arxiv_id":"1709.03999","date":"2017-09-12","proceeding":null,"authors":["Sowgat Muzahid","Gloria Fonseca","Amber Roberts","Benjamin Rosenwasser","Philipp Richter","Anand Narayanan","Chris Churchill","Jane Charlton"],"abstract":"We present a sample of 34 weak metal line absorbers at $z< 0.3$ complied via the simultaneous detections ($3\\sigma$) of the SiII$\\lambda1260$ and CII$\\lambda1334$ 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 using CLOUDY. The inferred densities and total hydrogen column densities are in the ranges of $-3.3 < \\log n_{\\rm H}/{\\rm cm^{-3}} < -2.4$ and $16.0 < \\log N_{\\rm H}/{\\rm cm^{-2}}<20.3$, respectively. The line of sight thicknesses of the absorbers have a wide range of $\\sim$1 pc$-$50 kpc with a median value of $\\sim$500 pc. The high-ionization OVI absorption, detected in 12/18 cases, always stems from a different gas-phase. Most importantly, 85% (50%) of these absorbers show a metallicity of $\\rm [Si/H] > -1.0$ (0.0). The fraction of systems showing high metallicity (i.e., $\\rm [Si/H]>-1.0$) in our sample is significantly higher than the HI-selected sample (Wotta et al. 2016) and the galaxy-selected sample (Prochaska et al. 2017) of absorbers probing the circum-galactic medium (CGM) at similar redshift. A search for galaxies has revealed a significant galaxy-overdensity around these weak absorbers compared to random places with a median impact parameter of 166 kpc to the nearest galaxy. Moreover, we find the presence of multiple galaxies in $\\sim80$% of the cases, suggesting group environments. The observed $d\\mathcal{N}/dz$ of $0.8\\pm0.2$ indicates that such metal-enriched, compact, dense structures are ubiquitous in the halos of low-$z$ galaxies that are in groups. We suggest that these are transient structures that are related to outflows and/or stripping of metal-rich gas from galaxies.","url_abs":"http://arxiv.org/abs/1709.03999v2","url_pdf":"http://arxiv.org/pdf/1709.03999v2.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"cos-weak-probing-the-cgm-using-analogs-of","repo_url":"https://github.com/wgao9/hypercontractivity","is_official":0,"mentioned_in_paper":0,"mentioned_in_github":1,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":null,"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}