A&A 458, 417-426 (2006)
DOI: 10.1051/0004-6361:20065187

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

S. Muller^{1, 2}, M. Guélin², M. Dumke^{3, 2}, R. Lucas² and F. Combes<sup>4

1</sup>  Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), PO Box 23-141, 106 Taipei, Taiwan
    e-mail: muller@asiaa.sinica.edu.tw
²  Institut de RadioAstronomie Millimétrique (IRAM), 300 rue de la piscine, 38406 St-Martin-d'Hères, France
³  European Southern Observatory (ESO), Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
⁴  Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France

(Received 13 March 2006 / Accepted 26 July 2006 )

Abstract
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.

Key words: quasars: individual: PKS 1830-211 -- quasars: absorption lines -- astrochemistry -- galaxies: ISM -- abundances -- ISM: molecules -- ISM: abundances

© ESO 2006

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