Vol 16, No 3 (2016) / Li

Oxygen isotopic ratios toward molecular clouds in the Galactic disk

Hai-Kun Li, Jiang-Shui Zhang, Zhi-Wei Liu, Deng-Rong Lu, Min Wang, Jin Wang

Abstract

We present our observations of the J = 1 − 0 rotation transitions in molecular isotopes C18O and C17O toward a sample of molecular clouds with different galactocentric distances, using the Delingha 13.7 m (DLH 13.7 m) telescope, administered by Purple Mountain Observatory, and its 9-beam SIS receiver. Complementary observations toward several sources with large galactocentric distance are obtained with the IRAM 30m and Mopra 22m telescopes. C18O/C17O abundance ratios reflecting the 18O/17O isotope ratios are obtained from integrated intensity ratios of C18O and C17O. We derived the ratio value for 13 sources covering a galactocentric distance range of 3 kpc to 16 kpc. In combination with our mapping results that provide a ratio value of 3.01±0.14 in the Galactic center region, it shows that the abundance ratio tends to increase with galactocentric distance, i.e., it supports a radial gradient along the Galactic disk for the abundance ratio. This is consistent with the inside-out formation scenario of our Galaxy. However, our results may suffer from small samples with large galactocentric distance. Combining our data with multitransition lines of C18O and C17O will be helpful for constraining opacities and abundances and further confirming the Galactic radial gradient shown by the isotope ratio 18O/17O.

Keywords


ISM: abundances — ISM: clouds — ISM: molecules — Galaxy: abundances — radio lines: ISM

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DOI: https://doi.org/10.1088/1674–4527/16/3/047

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