title: The first CO+image: I. Probing the HI/H2layer around the ultracompact HII region Mon R2.
abstract: 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 compare the CO+distribution with other species present in photon-dominated regions (PDR), such as [CII] 158µm, H2S(3) rotational line at 9.3µm, 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/H2interface. We have determined the CO+fractional abundance, relative to C+toward three positions. The abundances range from 0.1 to 1.9 ×10-10and are in good agreement with 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 blue-shifted with respect to the molecular gas velocity. We interpret this as a hint that the CO+is probing photo-evaporating clump surfaces.
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Sor Juana Inés de la Cruz 3, E-28049 Cantoblanco, Madrid, (Spain); Observatorio Astronómico Nacional, Apdo. 112, E-28803 Alcalá de Henares Madrid, (Spain).
authors.forename: S P
authors.initials: SP
authors.lastname: Treviño-Morales
authors.affiliation: Observatorio Astronómico Nacional, Apdo. 112, E-28803 Alcalá de Henares Madrid, (Spain).
authors.forename: A
authors.initials: A
authors.lastname: Fuente
authors.affiliation: I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, (Germany).
authors.forename: Á
authors.initials: Á
authors.lastname: Sánchez-Monge
authors.affiliation: CNRS; IRAP; 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4, (France); LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR8112, Place Janssen, 92190 Meudon Cedex, (France).
authors.forename: P
authors.initials: P
authors.lastname: Pilleri
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Sor Juana Inés de la Cruz 3, E-28049 Cantoblanco, Madrid, (Spain).
authors.forename: J R
authors.initials: JR
authors.lastname: Goicoechea
authors.affiliation: I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, (Germany).
authors.forename: V
authors.initials: V
authors.lastname: Ossenkopf-Okada
authors.affiliation: LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR8112, Place Janssen, 92190 Meudon Cedex, (France).
authors.forename: E
authors.initials: E
authors.lastname: Roueff
authors.affiliation: Centro de Astrobiología, E-28850 Torrejón de Ardoz, (Spain).
authors.forename: J R
authors.initials: JR
authors.lastname: Rizzo
authors.affiliation: LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR8112, Place Janssen, 92190 Meudon Cedex, (France).
authors.forename: M
authors.initials: M
authors.lastname: Gerin
authors.affiliation: CNRS; IRAP; 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4, (France); Université de Toulouse, UPS-OMP, IRAP, 31000 Toulouse, (France).
authors.forename: O
authors.initials: O
authors.lastname: Berné
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Sor Juana Inés de la Cruz 3, E-28049 Cantoblanco, Madrid, (Spain).
authors.forename: J
authors.initials: J
authors.lastname: Cernicharo
authors.affiliation: Instituto de Astrofísica de Andalucía, CSIC, E-18008, Granada, (Spain).
authors.forename: M
authors.initials: M
authors.lastname: Gónzalez-García
authors.affiliation: Instituto de Radioastronomía Milimétrica, Ave. Divina Pastora, 7, Local 20 18012, Granada (Spain).
authors.forename: C
authors.initials: C
authors.lastname: Kramer
authors.affiliation: Observatorio Astronómico Nacional, Apdo. 112, E-28803 Alcalá de Henares Madrid, (Spain).
authors.forename: S
authors.initials: S
authors.lastname: García-Burillo
authors.affiliation: Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, F-38406 Saint Martin d'Hères, (France).
authors.forename: J
authors.initials: J
authors.lastname: Pety
keywords: Astrochemistry – (ISM); ISM – Individual; Monoceros R2; Photo-dominated regions (PDRs) – HII region – Radio lines