arXiv 2102.131532021-02-25astro-ph.GA

分子cloudS（GEMS）中的气相元素丰度。IV。观察结果和统计趋势

Gas phase Elemental abundances in Molecular cloudS (GEMS). IV. Observational results and statistical trends

M. Rodríguez-Baras, A. Fuente, P. Riviére-Marichalar, D. Navarro-Almaida, P. Caselli, M. Gerin, C. Kramer, E. Roueff, V. Wakelam, G. Esplugues, S. García-Burill… 展开作者

M. Rodríguez-Baras, A. Fuente, P. Riviére-Marichalar, D. Navarro-Almaida, P. Caselli, M. Gerin, C. Kramer, E. Roueff, V. Wakelam, G. Esplugues, S. García-Burillo, R. Le Gal, S. Spezzano, T. Alonso-Albi, R. Bachiller, S. Cazaux, B. Commercon, J. R. Goicoechea, J. C. Loison, S. P. Treviño-Morales, O. Roncero, I. Jiménez-Serra, J. Laas, A. Hacar, J. Kirk, V. Lattanzi, R. Martín-Doménech, G. Muñoz-Caro, J. E. Pineda, B. Tercero, D. Ward-Thompson, M. Tafalla, N. Marcelino, J. Malinen, R. Friesen, B. M. Giuliano

备注：: 28 pages, 22 figures. Accepted for publication in A&A
发表信息：: A&A 648, A120 (2021)
DOI：: 10.1051/0004-6361/202040112

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摘要：

分子云中的气相元素丰度（GEMS）是一个IRAM 30米的大型程序，旨在估算金牛座、英仙座和猎户座的一组恒星形成细丝中的S、C、N和O消耗和气体电离度X（e-）。我们的近期目标是建立一个完整的数据库的分子丰度，可以作为一个观测基础，估计X（e-）和C，O，N和S的消耗，通过化学建模。对14个种的丰度进行了观测和计算（13 CO，C18 O，HCO+，H13 CO+，HC 18 O+，HCN，H13 CN，HNC，HCS+，CS，SO，34 SO，H2 S和OCS），覆盖AV 3到100等，n（H2）在这些云中有几个10 $^{3}$到10 $^6$ cm $^{-3}$，Tk范围为10到30 K，避开原恒星HII区和外流进行统计分析，以确定不同物种之间的一般趋势和物理参数。分子之间的关系显示出强烈的线性相关性，定义了三个不同的家族：（1）13 CO和C18 O;（2）H13 CO+，HC 18 O+，H13 CN和HNC;和（3）S-轴承分子。CO同位素丰度随气体动力学温度的升高而增加，直至TK 15 K.对于较高的温度，丰度保持恒定，分散系数为3。H13 CO+、HC 18 O+、H13 CN和HNC的丰度相互之间有很好的相关性，它们都随分子氢密度的增加而减少，遵循n（H2）$^{-0.8\pm0.2}$规律。含硫物种的丰度也随着n（H2）的增加而降低，其降低速率为（含硫/氢）气体n（H2）$^{-0.6\pm0.1}$。属于第2和第3组的分子丰度与气体温度没有任何明显的趋势。在分子云的尺度上，C18 O丰度是与云质量更好相关的数量。我们讨论了13 CO/C18 O，HCO+/H13 CO+，和H13 CO +/H13 CN丰度比作为恒星形成的化学诊断在外部星系的效用。

英文摘要：

Gas phase Elemental abundances in Molecular CloudS (GEMS) is an IRAM 30m Large Program designed to estimate the S, C, N, and O depletions and gas ionization degree, X(e-), in a set of star-forming filaments of Taurus, Perseus and Orion. Our immediate goal is to build up a complete database of molecular abundances that can serve as an observational basis for estimating X(e-) and the C, O, N, and S depletions through chemical modeling. We observed and derived the abundances of 14 species (13CO, C18O, HCO+, H13CO+, HC18O+, HCN, H13CN, HNC, HCS+, CS, SO, 34SO, H2S, and OCS) in 244 positions, covering the AV 3 to 100 mag, n(H2) a few 10$^{3}$ to 10$^6$ cm$^{-3}$, and Tk 10 to 30 K ranges in these clouds, avoiding protostars, HII regions, and outflows. A statistical analysis is carried out to identify general trends between different species and with physical parameters. Relations between molecules reveal strong linear correlations which define three different families: (1) 13CO and C18O; (2) H13CO+, HC18O+, H13CN, and HNC; and (3) the S-bearing molecules. The abundances of the CO isotopologs increase with the gas kinetic temperature until TK 15 K. For higher temperatures, the abundance remains constant with a scatter of a factor of 3. The abundances of H13CO+, HC18O+, H13CN, and HNC are well correlated with each other, and all of them decrease with molecular hydrogen density, following the law n(H2)$^{-0.8\pm0.2}$. The abundances of S-bearing species also decrease with n(H2) at a rate of (S-bearing/H)gas n(H2)$^{-0.6\pm0.1}$. The abundances of molecules belonging to groups 2 and 3 do not present any clear trend with gas temperature. At scales of molecular clouds, the C18O abundance is the quantity that better correlates with the cloud mass. We discuss the utility of the 13CO/C18O, HCO+/H13CO+, and H13CO+/H13CN abundance ratios as chemical diagnostics of star formation in external galaxies.

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