Probing isotopic ratios at z = 0.89: molecular line absorption in front of the quasar PKS 1830-211

S. Müller (1, 2) , Michel Guélin (2) , M. Dumke (3, 2) , R. Lucas (2) , Françoise Combes (4, 5, 6)

1 Institute of Astronomy and Astrophysics, Academia Sinica
2 IRAM - Institut de RadioAstronomie Millimétrique
3 European Southern Observatory
4 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
5 Galaxies et cosmologie
6 Dynamique des milieux interstellaires et plasmas stellaires

With the Plateau de Bure interferometer, we have measured the C, N, O and S isotopic abundance ratios in the arm of a spiral galaxy with a redshift of 0.89. The galaxy is seen face-on according to HST images. Its bulge intercepts the line of sight to the radio-loud quasar PKS 1830-211, giving rise at mm wavelengths to two Einstein images located each behind a spiral arm. The arms appear in absorption in the lines of several molecules, giving the opportunity to study the chemical composition of a galaxy only a few Gyr old. The isotopic ratios in this spiral galaxy differ markedly from those observed in the Milky Way. The ¹⁷O/¹⁸O and ¹⁴N/¹⁵N ratios are low, as one would expect from an object too young to let low mass stars play a major role in the regeneration of the gas.

Domaines: Astrophysique [astro-ph]

S. Müller, Michel Guélin, M. Dumke, R. Lucas, Françoise Combes. Probing isotopic ratios at z = 0.89: molecular line absorption in front of the quasar PKS 1830-211. Astronomy and Astrophysics - A&A, 2006, 458, pp.417-426. ⟨10.1051/0004-6361:20065187⟩. ⟨hal-03786655⟩