A&A 411, L465-L468 (2003)
DOI: 10.1051/0004-6361:20031442

Letter

First detections of extragalactic SO , NS and NO

S. Martín¹, R. Mauersberger¹, J. Martín-Pintado², S. García-Burillo³ and C. Henkel<sup>4

1</sup>  Instituto de Radioastronomía Milimétrica (IRAM), Avda. Divina Pastora 7 NC, 18012 Granada, Spain
²  Departamento de Astrofisíca Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain
³  Observatorio Astronómico Nacional (OAN), Apartado 1143, 28800 Alcalá de Henares, Madrid, Spain
⁴  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

(Received 8 August 2003 / Accepted 16 September 2003)

Abstract
We report the first detections of SO ₂, NS and NO in an extragalactic source, the nucleus of the starburst galaxy  NGC 253 . Five SO ₂ transitions, three groups of hyperfine components of NO and five of NS were detected. All three species show large abundances averaged over the inner 200 pc of NGC 253 . With a relative abundance of a few 10^-7, the emission of the NO molecule is similar or even larger than that found in Galactic star forming regions. The derived relative molecular abundances for each molecule have been compared with those of prototypical Galactic molecular clouds. These results seem to confirm that large scale shocks dominate the chemistry of these molecules in the nucleus of NGC 253 , ruling out a chemistry dominated by PDRs for the bulk of the gas.

Key words: ISM: molecules -- galaxies: individual: NGC 253 -- galaxies: ISM -- galaxies: starburst -- galaxies: abundances

Offprint request: S. Martín, martin@iram.es

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© ESO 2003

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