The first CO<SUP>+</SUP> image. I. Probing the HI/H<SUB>2</SUB> layer around the ultracompact HII region Mon R2

DOI:
10.1051/0004-6361/201628899
Publication date:
01/09/2016
Main author:
Treviño-Morales, S. P.
IAA authors:
Gónzalez-García, M.
Authors:
Treviño-Morales, S. P.;Fuente, A.;Sánchez-Monge, Á.;Pilleri, P.;Goicoechea, J. R.;Ossenkopf-Okada, V.;Roueff, E.;Rizzo, J. R.;Gerin, M.;Berné, O.;Cernicharo, J.;Gónzalez-García, M.;Kramer, C.;García-Burillo, S.;Pety, J.
Journal:
Astronomy and Astrophysics
Refereed:
Yes
Publication type:
Article
Volume:
593
Pages:
L12
Abstract:
The CO<SUP>+</SUP> 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<SUP>+</SUP> rotational emission toward the Mon R2 star-forming region. The CO<SUP>+</SUP> emission presents a clumpy ring-like morphology, arising from a narrow dense layer around the Hii region. We compared the CO<SUP>+</SUP> distribution with other species present in photon-dominated regions (PDR), such as [Cii] 158 μm, H<SUB>2</SUB> S(3) rotational line at 9.3 μm, polycyclic aromatic hydrocarbons (PAHs), and HCO<SUP>+</SUP>. We find that the CO<SUP>+</SUP> emission is spatially coincident with the PAHs and [Cii] emission. This confirms that the CO<SUP>+</SUP> emission arises from a narrow dense layer of the Hi/H<SUB>2</SUB> interface. We determined the CO<SUP>+</SUP> fractional abundance relative to C<SUP>+</SUP> toward three positions. The abundances range from 0.1 to 1.9 × 10<SUP>-10</SUP> and are in good agreement with the previous chemical model, which predicts that the production of CO<SUP>+</SUP> in PDRs only occurs in dense regions with high UV fields. The CO<SUP>+</SUP> 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<SUP>+</SUP> is probing photoevaporating clump surfaces.
Database: