Isotopic abundance of carbon in the DLA towards QSO B1331+170

Abstract

Chemical evolution models predict a gradual build-up of ${}^{13}$C in the universe, based on empirical nuclear reaction rates and assumptions on the properties of stellar populations. However, old metal-poor stars within the Galaxy contain more ${}^{13}$C than is predicted, suggesting that further refinements to the models are necessary. Gas at high redshift provides important supplementary information at metallicities $-2\lesssim$ [Fe/H] $\lesssim -1$, for which there are only a few measurements in the Galaxy. We obtained new, high-quality, VLT/ESPRESSO observations of the QSO B1331+170 and used them to measure ${}^{12}$C/${}^{13}$C in the damped Lyman-$\hat{I}\pm$ system (DLA) at $z_{abs}=1.776$, with [Fe/H]=-1.27. AI-VPFIT, an Artificial Intelligence tool based on genetic algorithms and guided by a spectroscopic information criterion, was used to explore different possible kinematic structures of the carbon gas. Three hundred independent AI-VPFIT models of the absorption system were produced using pre-set ${}^{12}$C/${}^{13}$C values, ranging from 4 to 500. Our results show that ${}^{12}$C/${}^{13}$C$=28.5_{-10.4}^{+51.5}$, suggesting a possibility of ${}^{13}$C production at low metallicity.

11 pages, 6 figures. Three appendices. To appear in MNRAS