Distribution of Water Vapor in Molecular Clouds. II
arXiv:2003.04897 · doi:10.3847/1538-4357/ab77b4
Abstract
The depth-dependent abundance of both gas-phase and solid-state water within dense, quiescent, molecular clouds is important to both the cloud chemistry and gas cooling. Where water is in the gas phase, it's free to participate in the network of ion-neutral reactions that lead to a host of oxygen-bearing molecules, and its many ortho and para energy levels make it an effective coolant for gas temperatures greater than 20K. Where water is abundant as ice on grain surfaces, and unavailable to cool the gas, significant amounts of oxygen are removed from the gas phase, suppressing the gas-phase chemical reactions that lead to a number of oxygen-bearing species, including O2. Models of FUV-illuminated clouds predict that the gas-phase water abundance peaks in the range Av ~3 and 8mag of the cloud surface, depending on the gas density and FUV field strength. Deeper within such clouds, water is predicted to exist mainly as ice on grain surfaces. More broadly, these models are used to analyze a variety of other regions, including outflow cavities associated with young stellar objects and the surface layers of protoplanetary disks. In this paper, we report the results of observational tests of FUV-illuminated cloud models toward the Orion Molecular Ridge and Cepheus B using data obtained from the Herschel Space Observatory and the Five College Radio Astronomy Observatory. Toward Orion, 2220 spatial positions were observed along the face-on Orion Ridge in the H2O 110-101 557GHz and NH3 J,K=1,0-0,0 572GHz lines. Toward Cepheus B, two strip scans were made in the same lines across the edge-on ionization front. These new observations demonstrate that gas-phase water exists primarily within a few magnitudes of dense cloud surfaces, strengthening the conclusions of an earlier study based on a much smaller data set, and indirectly supports the prediction that water ice is quite abundant in dense clouds.
arXiv comment59 pages, including 23 figures, Accepted for publication in ApJ
References in corpus (34)
- A computer program for fast non-LTE analysis of interstellar line spectra
- Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
- Observations of the Icy Universe
- Rotational quenching of CO due to H collisions
- Water, O2 and Ice in Molecular Clouds
- A PDR-Code Comparison Study
- Thermal Desorption of Water-Ice in the Interstellar Medium
- The anatomy of the Orion B Giant Molecular Cloud: A local template for studies of nearby galaxies
- First detection of water vapor in a pre-stellar core
- Herschel Measurements of Molecular Oxygen in Orion
- A study of deuterated water in the low-mass protostar IRAS16293-2422
- Molecular oxygen in the rho Ophiuchi cloud
- 3D-PDR: A new three-dimensional astrochemistry code for treating Photodissociation Regions
- N2H+(1-0) survey of massive molecular cloud cores
- Luminosity Functions of Spitzer Identified Protostars in Nine Nearby Molecular Clouds
- Multi-line detection of O2 toward rho Oph A
- CO Abundance Variations in the Orion Molecular Cloud
- Spitzer spectral line mapping of supernova remnants: I. Basic data and principal component analysis
- Chemistry and Radiative Transfer of Water in Cold, Dense Clouds
- Modeling molecular hyperfine line emission
- Submillimeter Wave Astronomy Satellite Observations of Extended Water Emission in Orion
- Water in low-mass star-forming regions with Herschel (WISH-LM): High-velocity H2O bullets in L1448-MM observed with HIFI
- A survey of HO, CO and CO ice features towards background stars and low mass YSOs using AKARI
- Observation of HCN hyperfine line anomalies towards low- and high-mass star-forming cores
- A New Determination of the Binding Energy of Atomic Oxygen on Dust Grain Surfaces: Experimental Results and Simulations
- Water Vapor around Sgr B2
- Herschel HIFI observations of O toward Orion: special conditions for shock enhanced emission
- Spitzer Imaging of the Nearby Rich Young Cluster, Cep OB3b
- The ratio of N(C18O) and Av in Chamaeleon I and III-B using 2MASS and SEST
- Water in Low-Mass Star-Forming Regions with Herschel: The Link Between Water Gas and Ice in Protostellar Envelopes
- Study of Photon Dominated Regions in Cepheus B
- Distribution of Water Vapor in Molecular Clouds
- Radiative Transfer of HCN: Interpreting observations of hyperfine anomalies
- A PDR model for the FIR mid- CO ladder with universal rotational temperature in star forming region
Cited by in corpus (6)
- Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
- Bottlenecks to interstellar sulfur chemistry: Sulfur-bearing hydrides in UV-illuminated gas and grains
- X-ray induced chemistry of water and related molecules in low-mass protostellar envelopes
- Anomalous HCN emission from warm giant molecular clouds
- Continuum, CO and Water vapour maps of the Orion Nebula. First millimetre spectral imaging with Concerto
- Weak, extended water vapor emission in the Horsehead nebula