{"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/the-occurrence-of-compact-groups-of-galaxies","title":"The Occurrence of Compact Groups of Galaxies Through Cosmic Time","arxiv_id":"1901.09041","date":"2019-01-25","proceeding":null,"authors":["Christopher D. Wiens","Trey V. Wenger","Panayiotis Tzanavaris","Kelsey E. Johnson","S. C. Gallagher","Liting Xiao"],"abstract":"We use the outputs of a semi-analytical model of galaxy formation run on the Millennium Simulation to investigate the prevalence of 3D compact groups (CGs) of galaxies from $z = 11$ to 0. Our publicly available code identifies CGs using the 3D galaxy number density, the mass ratio of secondary+tertiary to the primary member, mass density in a surrounding shell, the relative velocities of candidate CG members, and a minimum CG membership of three. We adopt \"default\" values for the first three criteria, representing the observed population of Hickson CGs at $z = 0$. The percentage of non-dwarf galaxies ($M > 5 \\times 10^{8}h^{-1}\\ M_{\\odot}$) in CGs peaks near $z \\sim 2$ for the default set, and between $z \\sim 1 - 3$ for other parameter sets. This percentage declines rapidly at higher redshifts ($z \\gtrsim 4$), consistent with the galaxy population as a whole being dominated by low-mass galaxies excluded from this analysis. According to the most liberal criteria, $\\lesssim 3\\%$ of non-dwarf galaxies are members of CGs at the redshift where the CG population peaks. Our default criteria result in a population of CGs at $z < 0.03$ with number densities and sizes consistent with Hickson CGs. Tracking identified CG galaxies and merger products to $z = 0$, we find that $\\lesssim 16\\%$ of non-dwarf galaxies have been CG members at some point in their history. Intriguingly, the great majority ($96\\%$) of $z = 2$ CGs have merged to a single galaxy by $z= 0$. There is a discrepancy in the velocity dispersions of Millennium Simulation CGs compared to those in observed CGs, which remains unresolved.","url_abs":"https://arxiv.org/abs/1901.09041v3","url_pdf":"https://arxiv.org/pdf/1901.09041v3.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":"the-occurrence-of-compact-groups-of-galaxies","repo_url":"https://github.com/cdw9bf/compactgroup","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"framework":"none","reach":null},{"paper_slug":"the-occurrence-of-compact-groups-of-galaxies","repo_url":"https://github.com/qtast/likeapj","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"framework":"none","reach":null},{"paper_slug":"the-occurrence-of-compact-groups-of-galaxies","repo_url":"https://github.com/tvwenger/millennium-tap-query","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"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}