Sulphur chemistry and molecular shocks: The case of NGC 1333-IRAS 2

¹ L3AB, Observatoire de Bordeaux, BP 89, 33270 Floirac, France e-mail: wakelam@mps.ohio-state.edu
² Laboratoire d'Astrophysique, Observatoire de Grenoble – BP 53, 38041 Grenoble Cedex 09, France
³ Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apartado Postal Postal 72-3 (Xangari), 58089 Morelia, Michoacán, Mexico

Received: 17 December 2004
Accepted: 23 February 2005

Abstract

We present SO and SO₂ observations in the region of the low mass protostar IRAS 2/NGC 1333. The East-West outflow originating from this source has been mapped in four transitions of both SO and SO₂. In addition, CS observations published in the literature have been used. We compute the SO, SO₂ and CS column densities and the physical conditions at several positions of the outflow using LTE and a non-LTE LVG approximations. The SO₂/SO and CS/SO abundance ratios are compared with the theoretical predictions of a chemical model adapted to the physical conditions in the IRAS 2 outflow. 
The SO₂/SO abundance ratios are constant in the two lobes of the outflow whereas CS/SO is up to 6 times lower in the shocked gas of the East lobe than in the West one. The comparison with the chemical model allows us to constrain the age of the outflow produced by IRAS 2 to ≤ yr. We find low densities and temperatures for the outflow of IRAS 2 (<10⁶ cm^-3 and ≤ K) from SO and SO₂ emission probably because the two molecules trace the cooled entrained material. The East lobe of the outflow shows denser gas compared to the West lobe. We also discuss some constraints on the depleted form of sulphur.