CO isotopes towards Galactic YSOs and HII regions

DOI

Aims. Determining molecular abundance ratios is important not only for the study of Galactic chemistry, but also because they are useful to estimate physical parameters in a large variety of interstellar medium environments. One of the most important molecules for tracing the molecular gas in the interstellar medium is CO, and the ^13^CO/C^18^O abundance ratio is usually used to estimate molecular masses and densities of regions with moderate to high densities. Nowadays isotope ratios are in general indirectly derived from elemental abundances ratios. We present the first ^13^CO/C^18^O abundance ratio study performed from CO isotope observations towards a large sample of Galactic sources of different natures at different locations. Methods. To study the ^13^CO/C^18^O abundance ratio, we used ^12^CO J=3-2 data obtained from the CO High-Resolution Survey, ^13^CO and C^18^O J=3-2 data from the ^13^CO/C^18^O (J=3-2) Heterodyne Inner Milky Way Plane Survey, and some complementary data extracted from the James Clerk Maxwell Telescope database. We analyzed a sample of 198 sources composed of young stellar objects (YSOs), and HII and diffuse HII regions as catalogued in the Red MSX Source Survey in 27.5{deg}<=l<=46.5{deg} and |b|<0.5{deg}. Results. Most of the analyzed sources are located in the galactocentric distance range 4.0-6.5kpc. We found that YSOs have, on average, lower ^13^CO/C^18^O abundance ratios than HII and diffuse HII regions. Taking into account that the gas associated with YSOs should be less affected by the radiation than in the case of the others sources, selective far-UV photodissociation of C^18^O is confirmed. The ^13^CO/C^18^O abundance ratios obtained in this work are systematically lower than those predicted from the known elemental abundance relations. These results will be useful in future studies of molecular gas related to YSOs and HII regions based on the observation of these isotopes.

Identifier
DOI http://doi.org/10.26093/cds/vizier.36120117
Source https://dc.g-vo.org/rr/q/lp/custom/CDS.VizieR/J/A+A/612/A117
Related Identifier https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/612/A117
Related Identifier http://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/612/A117
Metadata Access http://dc.g-vo.org/rr/q/pmh/pubreg.xml?verb=GetRecord&metadataPrefix=oai_b2find&identifier=ivo://CDS.VizieR/J/A+A/612/A117
Provenance
Creator Areal M.B.; Paron S.; Celis Pena M.; Ortega M.E.
Publisher CDS
Publication Year 2018
Rights https://cds.unistra.fr/vizier-org/licences_vizier.html
OpenAccess true
Contact CDS support team <cds-question(at)unistra.fr>
Representation
Resource Type Dataset; AstroObjects
Discipline Astrophysics and Astronomy; Interdisciplinary Astronomy; Interstellar medium; Natural Sciences; Physics; Stellar Astronomy