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Astron. Astrophys. 329, 443-450 (1998)

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Dense gas in nearby galaxies

XI. Interstellar 12C/13C ratios in the central regions of M 82 and IC 342*

C. Henkel 1, Y.-N. Chin 2, 3, R. Mauersberger 4 and J.B. Whiteoak 5, 6

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2 Institute of Astronomy and Astrophysics, Academia Sinica, P.O.Box 1-87 Nankang, 115 Taipei, Taiwan
3 Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
4 Steward Observatory, The University of Arizona, Tucson, AZ 85721, USA
5 Australia Telescope National Facility, Radiophysics Laboratories, P.O. Box 76, Epping, NSW 2121, Australia
6 Paul Wild Observatory, Australia Telescope National Facility, CSIRO, Locked Bag 194, Narrabri NSW 2390, Australia

Received 9 September 1996 / Accepted 21 July 1997


12C/13C line intensity ratios have been derived from several carbon-bearing molecules to confine the range of carbon and oxygen isotope abundance ratios toward the nuclear regions of two infrared bright galaxies. The most stringent limits are obtained from CN mm-wave emission lines. Supplementary measurements toward the Galactic center region indicate that overall I (12CN)/I (13CN) line intensity ratios are giving lower limits to the corresponding 12C/13C abundance ratio. Toward M 82 and IC 342, we find 12C/13C [FORMULA] 40 and [FORMULA] 30. Therefore the smaller 12C/13C ratio of our own Galactic center region (25) may not be typical for central regions of galaxies which are more luminous in the infrared. The 12C/13C limits and data from various isotopic species of CO also infer 15O/18O abundance ratios of [FORMULA] 90 and [FORMULA] 125 for M 82 and IC 342, respectively. From the I (HC14N)/I (HC15N) line intensity ratio, 14N/15N [FORMULA] 100 is derived for M 82.

Key words: ISM: abundances – galaxies: abundances – radio lines: ISM – radio lines: galaxies

* Based on observations with the IRAM 30-m telescope, Pico Veleta, Spain and the Swedish-ESO Submillimetre Telescope (SEST) at the European Southern Observatory (ESO), La Silla, Chile

Send offprint requests to:C. Henkel, p220hen@mpifr-bonn.mpg.de

© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997