Volume 458, Number 2, November I 2006
|Page(s)||417 - 426|
|Published online||12 September 2006|
Probing isotopic ratios at z = 0.89: molecular line absorption in front of the quasar PKS 1830-211
Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), PO Box 23-141, 106 Taipei, Taiwan e-mail: email@example.com
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
Accepted: 26 July 2006
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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