{"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/molecular-gas-properties-and-co-to-mathrm-h-2","title":"Molecular Gas Properties and CO-to-H2 Conversion Factors in the Central Kiloparsec of NGC 3351","arxiv_id":"2111.05844","date":"2021-11-10","proceeding":null,"authors":["Yu-Hsuan Teng","Karin M. Sandstrom","Jiayi Sun","Adam K. Leroy","L. Clifton Johnson","Alberto D. Bolatto","J. M. Diederik Kruijssen","Andreas Schruba","Antonio Usero","Ashley T. Barnes","Frank Bigiel","Guillermo A. Blanc","Brent Groves","Frank P. Israel","Daizhong Liu","Erik Rosolowsky","Eva Schinnerer","J. D. Smith","Fabian Walter"],"abstract":"The CO-to-H$_2$ conversion factor ($\\alpha_\\rm{CO}$) is critical to studying molecular gas and star formation in galaxies. The value of $\\alpha_\\rm{CO}$ has been found to vary within and between galaxies, but the specific environmental conditions that cause these variations are not fully understood. Previous observations on $\\sim$kpc scales revealed low values of $\\alpha_\\rm{CO}$ in the centers of some barred spiral galaxies, including NGC 3351. We present new ALMA Band 3, 6, and 7 observations of $^{12}$CO, $^{13}$CO, and C$^{18}$O lines on 100 pc scales in the inner $\\sim$2 kpc of NGC 3351. Using multi-line radiative transfer modeling and a Bayesian likelihood analysis, we infer the H$_2$ density, kinetic temperature, CO column density per line width, and CO isotopologue abundances on a pixel-by-pixel basis. Our modeling implies the existence of a dominant gas component with a density of $2{-}3\\times10^3$ $\\rm{cm^{-3}}$ in the central ${\\sim}$1 kpc and a high temperature of 30$-$60 K near the nucleus and near the contact points that connect to the bar-driven inflows. Assuming a CO/H$_2$ abundance of $3\\times10^{-4}$, our analysis yields $\\alpha_\\rm{CO}{\\sim}0.5{-}2.0$ $\\rm{M_\\odot\\,(K~km~s^{-1}~pc^2)^{-1}}$ with a decreasing trend with galactocentric radius in the central $\\sim$1 kpc. The inflows show a substantially lower $\\alpha_\\rm{CO} < 0.1$ $\\rm{M_\\odot\\,(K~km~s^{-1}~pc^2)^{-1}}$, likely due to lower optical depths caused by turbulence or shear in the inflows. Over the whole region, this gives an intensity-weighted $\\alpha_\\rm{CO}$ of ${\\sim}1.5$ $\\rm{M_\\odot\\,(K~km~s^{-1}~pc^2)^{-1}}$, which is similar to previous dust modeling based results at kpc scales. This suggests that low $\\alpha_\\rm{CO}$ on kpc scales in the centers of some barred galaxies may be due to the contribution of low optical depth CO emission in bar-driven inflows.","url_abs":"https://arxiv.org/abs/2111.05844v2","url_pdf":"https://arxiv.org/pdf/2111.05844v2.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":"molecular-gas-properties-and-co-to-mathrm-h-2","repo_url":"https://github.com/ElthaTeng/multiline-ngc3351","is_official":1,"mentioned_in_paper":1,"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}