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Metallicity dependence of the CO-to-H2 and the [CI]-to-H2 conversion factors in galaxies

文献类型：期刊论文

作者Bisbas, Thomas G.1; Zhang, Zhi-Yu2,3; Kyrmanidou, Maria-Christina4; Luo, Gan5; Zhao YH(赵应和)6,7; Topkaras, Theodoros8; Jiang, Xue-Jian1; Quan, Donghui1; Li, Di9
刊名ASTRONOMY & ASTROPHYSICS
出版日期2025-05-19
卷号697
关键词astrochemistry radiative transfer methods: numerical ISM: general photon-dominated region (PDR)
ISSN号0004-6361
DOI10.1051/0004-6361/202554067
产权排序第6完成单位
文献子类Article
英文摘要Understanding the molecular gas content in the interstellar medium (ISM) is crucial for studying star formation and galaxy evolution. The CO-to-H-2 (X-CO) and the [CI]-to-H-2 (X-CI) conversion factors are widely used to estimate the molecular mass content in galaxies. However, these factors depend on many environmental parameters in the ISM, such as metallicity, cosmic-ray ionization rate, and far-ultraviolet (FUV) radiation field, in particular, in the low-metallicity ISM that is found at large galactocentric radii and in early-type galaxies. This work investigates the dependence of X-CO and X-CI on the environmental parameters of the ISM, with a focus on the low-metallicity alpha-enhanced ISM ([C/O] < 0), to provide improved tracers of molecular gas under diverse conditions. We used the statistical algorithm PDFCHEM, coupled with a database of photodissociation region (PDR) models generated with the 3D-PDR astrochemical code. The models account for a wide range of metallicities, dust-to-gas mass ratios, FUV intensities, and cosmic-ray ionization rates. The conversion factors were computed by integrating the PDR properties over log-normal column density distributions (A(V)-PDFs) that represent various cloud types. The X-CO factor increases significantly with decreasing metallicity. It exceeds similar to 1000 times the Galactic value at [O/H] = -1.0 under alpha-enhanced conditions, as opposed to similar to 300 times under non-alpha-enhanced conditions ([C/O] = 0). In contrast, X-CI varies more gradually with metallicity, which makes it a more reliable tracer of molecular gas in metal-poor environments under most conditions. The fraction of CO-dark molecular gas increases dramatically in low-metallicity regions, where it exceeds 90% at [O/H] = -1.0, in particular, in diffuse clouds and environments with strong FUV radiation fields. The results highlight the limitations of CO as a molecular gas tracer in the metal-poor ISM and demonstrate the potential of [CI] (1-0) as a complementary tracer. The use of metallicity-dependent X-CO and X-CI factors as provided by this study is recommended for accurately estimating molecular gas masses in diverse environments. We recommend the use of the log(10)X(CO) similar or equal to -2.41 Z + 41.3 relation for the CO-to-H-2 conversion factor and the log(10)X(CI) similar or equal to -0.99 Z + 29.7 relation for the [CI]-to-H-2 conversion factor, where Z = 12 + log(10)(O/H).
学科主题天文学 ; 天体物理学 ; 高能天体物理学 ; 星系与宇宙学
URL标识查看原文
出版地17, AVE DU HOGGAR, PA COURTABOEUF, BP 112, F-91944 LES ULIS CEDEX A, FRANCE
WOS关键词TOTAL MOLECULAR GAS ; COLUMN DENSITY DISTRIBUTION ; STAR-FORMING GALAXIES ; CO-DARK GAS ; X-CO ; CHEMICAL EVOLUTION ; LINE-INTENSITIES ; CARBON-MONOXIDE ; DUST CONTINUUM ; MILKY-WAY
资助项目National Key Research and Development Program of Chinahttps://doi.org/10.13039/501100012166[2023YFA1608204]; National Key Research & Development (R&D) Programme of China[2023R01008]; Leading Innovation and Entrepreneurship Team of Zhejiang Province of China[Ts 17/2-1]; German Deutsche Forschungsgemeinschaft, DFG[11988101]; National Natural Science Foundation of China (NSFC); Programme for Innovative Talents, Enterpreneur in Jiangsu[500700252]; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)
WOS研究方向Astronomy & Astrophysics
语种英语
WOS记录号WOS:001490583400001
出版者EDP SCIENCES S A
资助机构National Key Research and Development Program of Chinahttps://doi.org/10.13039/501100012166[2023YFA1608204] ; National Key Research & Development (R&D) Programme of China[2023R01008] ; Leading Innovation and Entrepreneurship Team of Zhejiang Province of China[Ts 17/2-1] ; German Deutsche Forschungsgemeinschaft, DFG[11988101] ; National Natural Science Foundation of China (NSFC) ; Programme for Innovative Talents, Enterpreneur in Jiangsu[500700252] ; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)
版本出版稿
源URL[http://ir.ynao.ac.cn/handle/114a53/28306]  
专题星系类星体研究组
作者单位1.Research Center for Astronomical Computing, Zhejiang Laboratory, Hangzhou 311000, China;
2.School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China;
3.Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, China;
4.Department of Physics, Aristotle University of Thessaloniki, Greece;
5.Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38400 Saint-Martin-d’Héres, France;
6.Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011, China;
7.Key Laboratory of Radio Astronomy and Technology (Chinese Academy of Sciences), A20 Datun Road,Chaoyang District, Beijing 100101, PR China;
8.I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany;
9.New Cornerstone Science Laboratory, Department of Astronomy, Tsinghua University, Beijing 100084, China;
10.National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
推荐引用方式
GB/T 7714		 Bisbas, Thomas G.,Zhang, Zhi-Yu,Kyrmanidou, Maria-Christina,et al. Metallicity dependence of the CO-to-H2 and the [CI]-to-H2 conversion factors in galaxies[J]. ASTRONOMY & ASTROPHYSICS,2025,697.
APA Bisbas, Thomas G..,Zhang, Zhi-Yu.,Kyrmanidou, Maria-Christina.,Luo, Gan.,赵应和.,...&Li, Di.(2025).Metallicity dependence of the CO-to-H2 and the [CI]-to-H2 conversion factors in galaxies.ASTRONOMY & ASTROPHYSICS,697.
MLA Bisbas, Thomas G.,et al."Metallicity dependence of the CO-to-H2 and the [CI]-to-H2 conversion factors in galaxies".ASTRONOMY & ASTROPHYSICS 697(2025).

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来源：云南天文台

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