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

¹ Department of Earth and Space SciencesChalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
e-mail: swallstrom@asiaa.sinica.edu.tw
² Institut de Radio Astronomie Millimétrique, 300 rue de la piscine, 38406 St Martin d’ Hères, France
³ École Normale Supérieure/LERMA, 24 rue Lohmond, 75005 Paris, France

Received: 31 March 2016
Accepted: 14 July 2016

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 PKS 1830−211. 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.