Isotopic ratios at z=0.68 from molecular absorption lines toward B 0218+357

TL;DR

This study measures isotopic ratios of key elements in a distant galaxy, revealing insights into stellar nucleosynthesis and chemical evolution, and comparing these ratios to local and other intermediate-redshift environments.

Contribution

First measurement of isotopic ratios at z=0.68 using molecular absorption lines, providing new data for understanding cosmic chemical evolution.

Findings

Ratios differ from Galactic interstellar medium

Ratios are similar to those in a z=0.89 absorber and local starburst galaxies

Results constrain models of nucleosynthesis and chemical evolution

Abstract

Isotopic ratios of heavy elements are a key signature of the nucleosynthesis processes in stellar interiors. The contribution of successive generations of stars to the metal enrichment of the Universe is imprinted on the evolution of isotopic ratios over time. We investigate the isotopic ratios of carbon, nitrogen, oxygen, and sulfur through millimeter molecular absorption lines arising in the z=0.68 absorber toward the blazar B 0218+357. We find that these ratios differ from those observed in the Galactic interstellar medium, but are remarkably close to those in the only other source at intermediate redshift for which isotopic ratios have been measured to date, the z=0.89 absorber in front of PKS1830-211. The isotopic ratios in these two absorbers should reflect enrichment mostly from massive stars, and they are indeed close to the values observed toward local starburst galaxies. Our measurements set constraints on nucleosynthesis and chemical evolution models.