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Title: The {sup 12}C/{sup 13}C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

Abstract

A study has been conducted of {sup 12}C/{sup 13}C ratios in five complex molecules in the Galactic center. H{sub 2}CS, CH{sub 3}CCH, NH{sub 2}CHO, CH{sub 2}CHCN, and CH{sub 3}CH{sub 2}CN and their {sup 13}C-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 {sup 12}C species and 2–54 for {sup 13}C-substituted analogs were modeled in a global radiative transfer analysis. All five molecules were found to consistently exhibit two velocity components near V {sub LSR} ∼ 64 and 73 km s{sup −1}, with column densities ranging from N {sub tot} ∼ 3 × 10{sup 14} − 4 × 10{sup 17} cm{sup −2} and ∼2 × 10{sup 13} − 1 × 10{sup 17} cm{sup −2} for the {sup 12}C and {sup 13}C species, respectively. Based on 14 different isotopic combinations, ratios were obtained in the range {sup 12}C/{sup 13}C = 15 ± 5 to 33 ± 13, with an average value of 24 ± 7, based on comparison of column densities. These measurements better anchor the {sup 12}C/{sup 13}C ratiomore » at the Galactic center, and suggest a slightly revised isotope gradient of {sup 12}C/{sup 13}C = 5.21(0.52) D {sub GC} + 22.6(3.3). As indicated by the column densities, no preferential {sup 13}C enrichment was found on the differing carbon sites of CH{sub 3}CCH, CH{sub 2}CHCN, and CH{sub 3}CH{sub 2}CN. Because of the elevated temperatures in Sgr B2(N), {sup 13}C 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.« less

Authors:
;  [1];  [2]
  1. Department of Chemistry and Biochemistry, University of Arizona, 1305 E. 4th Street, Tucson, AZ 85719 (United States)
  2. Department of Astronomy, Arizona Radio Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
Publication Date:
OSTI Identifier:
22663207
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 845; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; CARBON 12; CARBON 13; COMPARATIVE EVALUATIONS; DENSITY; ENRICHMENT; EVOLUTION; FRACTIONATION; GALAXIES; ISOTOPE RATIO; ISOTOPIC EXCHANGE; MOLECULES; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; RADIANT HEAT TRANSFER; TELESCOPES; VELOCITY

Citation Formats

Halfen, D. T., Ziurys, L. M., and Woolf, N. J., E-mail: halfend@email.arizona.edu. The {sup 12}C/{sup 13}C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA816B.
Halfen, D. T., Ziurys, L. M., & Woolf, N. J., E-mail: halfend@email.arizona.edu. The {sup 12}C/{sup 13}C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry. United States. doi:10.3847/1538-4357/AA816B.
Halfen, D. T., Ziurys, L. M., and Woolf, N. J., E-mail: halfend@email.arizona.edu. Sun . "The {sup 12}C/{sup 13}C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry". United States. doi:10.3847/1538-4357/AA816B.
@article{osti_22663207,
title = {The {sup 12}C/{sup 13}C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry},
author = {Halfen, D. T. and Ziurys, L. M. and Woolf, N. J., E-mail: halfend@email.arizona.edu},
abstractNote = {A study has been conducted of {sup 12}C/{sup 13}C ratios in five complex molecules in the Galactic center. H{sub 2}CS, CH{sub 3}CCH, NH{sub 2}CHO, CH{sub 2}CHCN, and CH{sub 3}CH{sub 2}CN and their {sup 13}C-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 {sup 12}C species and 2–54 for {sup 13}C-substituted analogs were modeled in a global radiative transfer analysis. All five molecules were found to consistently exhibit two velocity components near V {sub LSR} ∼ 64 and 73 km s{sup −1}, with column densities ranging from N {sub tot} ∼ 3 × 10{sup 14} − 4 × 10{sup 17} cm{sup −2} and ∼2 × 10{sup 13} − 1 × 10{sup 17} cm{sup −2} for the {sup 12}C and {sup 13}C species, respectively. Based on 14 different isotopic combinations, ratios were obtained in the range {sup 12}C/{sup 13}C = 15 ± 5 to 33 ± 13, with an average value of 24 ± 7, based on comparison of column densities. These measurements better anchor the {sup 12}C/{sup 13}C ratio at the Galactic center, and suggest a slightly revised isotope gradient of {sup 12}C/{sup 13}C = 5.21(0.52) D {sub GC} + 22.6(3.3). As indicated by the column densities, no preferential {sup 13}C enrichment was found on the differing carbon sites of CH{sub 3}CCH, CH{sub 2}CHCN, and CH{sub 3}CH{sub 2}CN. Because of the elevated temperatures in Sgr B2(N), {sup 13}C 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.},
doi = {10.3847/1538-4357/AA816B},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 845,
place = {United States},
year = {2017},
month = {8}
}