A study has been conducted of 12C/13C ratios in five complex molecules in the Galactic center. H2CS, CH3CCH,
NH2CHO, CH2CHCN, and CH3CH2CN and their 13C-substituted species have been observed in numerous
transitions at 1, 2, and 3 mm, acquired in a spectral-line survey of Sgr B2(N), conducted with the telescopes of the
Arizona Radio Observatory (ARO). Between 22 and 54 individual, unblended lines for the 12C species and 2–54
for 13C-substituted analogs were modeled in a global radiative transfer analysis. All five molecules were found
to consistently exhibit two velocity components near VLSR ∼ 64 and 73 km s−1, with column densities ranging
from Ntot ∼ 3 × 1014 − 4 × 1017 cm−2 and ∼2 × 1013 − 1 × 1017 cm−2 for the 12C and 13C species, respectively.
Based on 14 different isotopic combinations, ratios were obtained in the range 12C/13C = 15 ± 5 to 33 ± 13, with
an average value of 24 ± 7, based on comparison of column densities. These measurements better anchor the 12C/13C ratio at the Galactic center, and suggest a slightly revised isotope gradient of 12C/13C = 5.21(0.52) DGC +
22.6(3.3). As indicated by the column densities, no preferential 13C enrichment was found on the differing carbon
sites of CH3CCH, CH2CHCN, and CH3CH2CN. Because of the elevated temperatures in Sgr B2(N), 13C isotopic
substitution is effectively “scrambled,” diminishing chemical fractionation effects. The resulting ratios thus reflect
stellar nucleosynthesis and Galactic chemical evolution, as is likely the case for most warm clouds.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/625777 |
| Date | 22 August 2017 |
| Creators | Halfen, D. T., Woolf, N. J., Ziurys, L. M. |
| Contributors | Univ Arizona, Dept Chem & Biochem, Univ Arizona, Dept Astron, Arizona Radio Observ |
| Publisher | IOP PUBLISHING LTD |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | Article |
| Rights | © 2017. The American Astronomical Society. All rights reserved. |
| Relation | http://stacks.iop.org/0004-637X/845/i=2/a=158?key=crossref.cc27842d09d8ba283cc3b7bebee9da44 |
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