{"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/evidence-that-hydra-i-is-a-tidally-disrupting","title":"Evidence That Hydra I is a Tidally Disrupting Milky Way Dwarf Galaxy","arxiv_id":"1509.06391","date":"2015-09-21","proceeding":null,"authors":["Jonathan R. Hargis","B. Kimmig","B. Willman","N. Caldwell","M. G. Walker","J. Strader","D. J. Sand","C. J. Grillmair","J. H. Yoon"],"abstract":"The Eastern Banded Structure (EBS) and Hydra~I halo overdensity are very nearby (d $\\sim$ 10 kpc) objects discovered in SDSS data. Previous studies of the region have shown that EBS and Hydra I are spatially coincident, cold structures at the same distance, suggesting that Hydra I may be the EBS's progenitor. We combine new wide-field DECam imaging and MMT/Hectochelle spectroscopic observations of Hydra I with SDSS archival spectroscopic observations to quantify Hydra I's present-day chemodynamical properties, and to infer whether it originated as a star cluster or dwarf galaxy. While previous work using shallow SDSS imaging assumed a standard old, metal-poor stellar population, our deeper DECam imaging reveals that Hydra~I has a thin, well-defined main sequence turnoff of intermediate age ($\\sim 5-6$ Gyr) and metallicity ([Fe/H] = $-0.9$ dex). We measure statistically significant spreads in both the iron and alpha-element abundances of $\\sigma_{[Fe/H]} = 0.13 \\pm 0.02$ dex and $\\sigma_{[\\alpha/{\\rm Fe}]} = 0.09 \\pm 0.03$ dex, respectively, and place upper limits on both the rotation and its proper motion. Hydra~I's intermediate age and [Fe/H] -- as well as its low [$\\alpha$/Fe], apparent [Fe/H] spread, and present-day low luminosity -- suggest that its progenitor was a dwarf galaxy, which subsequently lost more than $99.99\\%$ of its stellar mass.","url_abs":"http://arxiv.org/abs/1509.06391v1","url_pdf":"http://arxiv.org/pdf/1509.06391v1.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":"evidence-that-hydra-i-is-a-tidally-disrupting","repo_url":"https://github.com/bkimmig/clumpy","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}