A line confusion-limited millimeter survey of Orion KL^⋆

III. Sulfur oxide species

¹ Centro de Astrobiología (CSIC-INTA), Ctra. de Torrejón-Ajalvir, km. 4, 28850 Torrejón de Ardoz, Madrid Spain
e-mail: espluguesbg@cab.inta-csic.es
² Institut de Cències de l’Espai (CSIC-IEEC), Campus UAB-Facultat de Ciencies, Torre C5-parell 2, 08193 Bellaterra, Barcelona, Spain
³ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA

Received: 13 February 2013
Accepted: 28 May 2013

Abstract

Context. We present a study of the sulfur-bearing species detected in a line confusion-limited survey towards Orion KL performed with the IRAM 30-m telescope in the frequency range 80−281 GHz.

Aims. This study is part of an analysis of the line survey divided into families of molecules. Our aim is to derive accurate physical conditions, as well as molecular abundances, in the different components of Orion KL from observed SO and SO₂ lines.

Methods. As a starting point, we assumed local thermodynamic equilibrium (LTE) conditions obtain rotational temperatures. We then used a radiative transfer model, assuming either LVG or LTE excitation to derive column densities of these molecules in the different components of Orion KL.

Results. We have detected 68 lines of SO, ³⁴SO, ³³SO, and S¹⁸O and 653 lines of SO₂, ³⁴SO₂, ³³SO₂, SO¹⁸O, and SO₂ν₂ = 1. We provide column densities for all of them and also upper limits for the column densities of S¹⁷O, ³⁶SO, ³⁴S¹⁸O, SO¹⁷O, and ³⁴SO₂ν₂ = 1 and for several undetected sulfur-bearing species. In addition, we present 2′ × 2′ maps around Orion IRc2 of SO₂ transitions with energies from 19 to 131 K and also maps with four transitions of SO, ³⁴SO, and ³⁴SO₂. We observe an elongation of the gas along the NE-SW direction. An unexpected emission peak appears at 20.5 km s^-1 in most lines of SO and SO₂. A study of the spatial distribution of this emission feature shows that it is a new component of a few arcseconds (~5″) in diameter, which lies  ~4″ west of IRc2. We suggest the emission from this feature is related to shocks associated to the BN object.

Conclusions. The highest column densities for SO and SO₂ are found in the high-velocity plateau (a region dominated by shocks) and in the hot core. These values are up to three orders of magnitude higher than the results for the ridge components. We also find high column densities for their isotopologues in both components. Therefore, we conclude that SO and SO₂ are good tracers, not only of regions affected by shocks, but also of regions with warm dense gas (hot cores).