文章基本信息

标题：The first CO+ image - I. Probing the HI/H2 layer around the ultracompact HII region Mon R2
其他标题：I. Probing the HI/H2 layer around the ultracompact HII region Mon R2
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作者：S. P. Treviño-Morales ; S. P. Treviño-Morales ; A. Fuente 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2016
卷号：593
页码：1-6
DOI：10.1051/0004-6361/201628899
语种：English
出版社：EDP Sciences
摘要：The CO+ reactive ion is thought to be a tracer of the boundary between a Hii region and the hot molecular gas. In this study, we present the spatial distribution of the CO+ rotational emission toward the Mon R2 star-forming region. The CO+ emission presents a clumpy ring-like morphology, arising from a narrow dense layer around the Hii region. We compared the CO+ distribution with other species present in photon-dominated regions (PDR), such as [Cii] 158 μm, H2 S(3) rotational line at 9.3 μm, polycyclic aromatic hydrocarbons (PAHs), and HCO+. We find that the CO+ emission is spatially coincident with the PAHs and [Cii] emission. This confirms that the CO+ emission arises from a narrow dense layer of the Hi/H2 interface. We determined the CO+ fractional abundance relative to C+ toward three positions. The abundances range from 0.1 to 1.9 × 10-10 and are in good agreement with the previous chemical model, which predicts that the production of CO+ in PDRs only occurs in dense regions with high UV fields. The CO+ linewidth is larger than those found in molecular gas tracers, and their central velocity are blueshifted with respect to the molecular gas velocity. We interpret this as a hint that the CO+ is probing photoevaporating clump surfaces.
关键词：astrochemistry;photon-dominated region;Hii regions;radio lines: ISM