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arXiv 2502.00538astro-ph.GA
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前恒星核中甲醛与甲醇的相关性

Correlation between formaldehyde and methanol in prestellar cores

A. F. Punanova, K. Borshcheva, G. S. Fedoseev, P. Caselli, D. S. Wiebe, A. I. Vasyunin

备注：
15 pages, 10 figures. Accepted for publication in MNRAS
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AI总结：

本研究利用IRAM 30米望远镜观测L1495纤维结构中七个致密核的甲醛分布，估算其柱密度与丰度以约束化学模型，修正后的MONACO模型将甲醛与甲醇丰度再现误差控制在一个数量级内。

摘要：

甲醛是空间中许多复杂有机分子（COMs）形成路径的关键前体。它也是CO加氢序列的中间步骤，该序列在冷致密的前恒星核中导致星际尘埃表面形成甲醇，而这些核心正是原始冰形成的地方。各种化学模型成功再现了冷核中的COMs丰度，但它们始终将甲醛丰度高估约一个数量级。这导致天体化学模拟中得到的H2CO:CH3OH丰度比与观测值呈反比。在本研究中，我们展示了使用IRAM 30米望远镜对L1495纤维结构中七个致密核进行观测得到的甲醛观测图均匀数据集。解析分子的空间分布对于测试化学模型至关重要。我们仔细估算了甲醛的柱密度和丰度，为冷核化学模型提供可靠的观测约束。通过大量测试，我们旨在约束更新后的化学模型MONACO，使其更好地符合观测到的甲醛丰度及其与甲醇的比值。特别是，我们详细探讨了低温下CH3 + O反应的分支比。修正后的MONACO模型将甲醇和甲醛的丰度再现误差控制在约一个数量级内。然而，该模型倾向于过量产生甲醛并低估甲醇。因此，模型系统性地高估了H2CO:CH3OH比值，尽管该比值仍保持在观测推导值的一个数量级范围内。

英文摘要：

Formaldehyde is a key precursor in the formation routes of many complex organic molecules (COMs) in space. It is also an intermediate step in CO hydrogenation sequence that leads to methanol formation on the surface of interstellar grains in cold dense prestellar cores where pristine ices are formed. Various chemical models successfully reproduce the COMs abundances in cold cores, however, they consistently overpredict the abundance of formaldehyde by an order of magnitude. This results in an inverse H2CO:CH3OH abundance ratios obtained in the astrochemical simulations as compared to the observed values. In this work, we present a homogeneous data set of formaldehyde observational maps obtained towards seven dense cores in the L1495 filament with the IRAM 30 m telescope. Resolving the spatial distribution of the molecules is essential to test the chemical models. We carefully estimate the formaldehyde column densities and abundances to put reliable observational constraints on the chemical models of cold cores. Through numerous tests, we aim to constrain the updated chemical model MONACO to better align with the observed formaldehyde abundance and its ratio to methanol. In particular, we elaborate on the branching ratio of the CH3 + O reaction at low temperatures. The revised MONACO model reproduces abundances of both methanol and formaldehyde within an order of magnitude. However the model tends to overproduce formaldehyde and underpredict methanol. Consequently, the model systematically overestimates the H2CO:CH3OH ratio, although it remains within an order of magnitude of the values derived from observations.

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