Herschel / HIFI observations of CO, H2O and NH3 in Mon R2
arXiv:1206.1249 · doi:10.1051/0004-6361/201118481
Abstract
Context. Mon R2 is the only ultracompact HII region (UCHII) where the associated photon-dominated region (PDR) can be resolved with Herschel. Due to its brightness and proximity, it is the best source to investigate the chemistry and physics of highly UV-irradiated PDRs. Aims. Our goal is to estimate the abundance of H2O and NH3 in this region and investigate their origin. Methods. We present new observations obtained with HIFI and the IRAM-30m telescope. Using a large velocity gradient approach, we model the line intensities and derive an average abundance of H2O and NH3 across the region. Finally, we model the line profiles with a non-local radiative transfer model and compare these results with the abundance predicted by the Meudon PDR code. Results. The variations of the line profiles and intensities indicate complex geometrical and kinematical patterns. The H2O lines present a strong absorption at the ambient velocity and emission in high velocity wings towards the HII region. The spatial distribution of the o-H2^18O line shows that the its emission arises in the PDR surrounding the HII region. By modeling the o-H2^18O emission we derive a mean abundance of o-H2O of ~10^-8 relative to H2. The ortho-H2O abundance is however larger, ~1x10^-7, in the high velocity wings. Possible explanations for this larger abundance include an expanding hot PDR and/or an outflow. Ammonia seems to be present only in the envelope with an average abundance of ~2x10^-9 relative to H2. Conclusions. The Meudon PDR code can account for the measured water abundance in the high velocity gas as long as we assume that it originates from a <1 mag hot expanding layer of the PDR, i.e. that the outflow has only a minor contribution to this emission. To explain the abundances in the rest of the cloud the molecular freeze out and grain surface chemistry would need to be included.
12 pages, 7 figures, 3 tables. Accepted for publication in A&A. Abstract shortened. Updated references, language editing applied in v2
References in corpus (3)
Cited by in corpus (19)
- Interstellar water chemistry: from laboratory to observations
- Interstellar Hydrides
- Herschel/HIFI observations of [CII] and [13CII] in PDRs
- Dynamics of cluster-forming hub-filament systems: The case of the high-mass star-forming complex Monoceros R2
- Abundances of sulphur molecules in the Horsehead nebula. First NS+ detection in a photodissociation region
- Spectroscopically resolved far-IR observations of the massive star-forming region G5.89--0.39
- Probing the role of polycyclic aromatic hydrocarbons in the photoelectric heating within photodissociation regions
- Spatial distribution of small hydrocarbons in the neighborhood of the Ultra Compact HII region Monoceros R2
- Deuteration around the ultracompact HII region Mon R2
- Velocity resolved [CII], [CI], and CO observations of the N159 star-forming region in the Large Magellanic Cloud: a complex velocity structure and variation of the column densities
- Velocity profiles of [CII], [CI], CO, and [OI] and physical conditions in four star-forming regions in the Large Magellanic Cloud
- Far-infrared observations of a massive cluster forming in the Monoceros R2 filament hub
- From forced collapse to H ii region expansion in Mon R2: Envelope density structure and age determination with Herschel
- Kinematics of the ionized-to-neutral interfaces in Monoceros R2
- The PDR structure and kinematics around the compact HII regions S235A and S235C with [CII], [13CII], [OI] and HCO+ line profiles
- The first CO+ image: Probing the HI/H2 layer around the ultracompact HII region Mon R2
- Probing the kinematics and chemistry of the hot core Mon R 2 IRS 3 using ALMA observations
- The [OI] fine structure line profiles in Mon R2 and M17 SW: the puzzling nature of cold foreground material identified by [12CII] self-absorption
- Weak, extended water vapor emission in the Horsehead nebula