TY - JOUR
T1 - The 12C/13C Ratio in Sgr B2(N)
T2 - Constraints for Galactic Chemical Evolution and Isotopic Chemistry
AU - Halfen, D. T.
AU - Woolf, N. J.
AU - Ziurys, L. M.
N1 - Funding Information:
We thank the staff of ARO for making these observations possible. This research was supported by NSF grants AST-1515568 and AST-1140030. The Kitt Peak 12 m and the SMT are operated by the Arizona Radio Observatory (ARO), with partial support through the NSF University Radio Observatories (URO) program (AST-1140030). The work was also supported by NASA under Agreement No. NNX15AD94G issued through the Science Mission Directorate interdivisional initiative Nexus for Exoplanet System Science (NExSS).
Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved..
PY - 2017/8/20
Y1 - 2017/8/20
N2 - 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 V LSR ∼ 64 and 73 km s-1, with column densities ranging from N tot ∼ 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) D GC + 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.
AB - 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 V LSR ∼ 64 and 73 km s-1, with column densities ranging from N tot ∼ 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) D GC + 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.
KW - Galaxy: evolution
KW - ISM: molecules
KW - astrochemistry
KW - line: identification
KW - methods: observational
KW - nuclear reactions, nucleosynthesis, abundances
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U2 - 10.3847/1538-4357/aa816b
DO - 10.3847/1538-4357/aa816b
M3 - Article
AN - SCOPUS:85028732654
VL - 845
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - 158
ER -