Letter to the Editor

First detections of extragalactic SO₂, NS and NO

¹ 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

Corresponding author: S. Martín, martin@iram.es

Received: 8 August 2003
Accepted: 16 September 2003

Abstract

We report the first detections of SO₂, NS and NO in an extragalactic source, the nucleus of the starburst galaxy NGC 253. Five SO₂ 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.