A&A 517, A96 (2010) DOI: 10.1051/0004-6361/200913501 c  ESO 2010 Astronomy & Astrophysics A line confusion limited millimeter survey of Orion KL I. Sulfur carbon chains ⋆ B. Tercero, J. Cernicharo, J. R. Pardo, and J. R. Goicoechea Centro de Astrobiología (CSIC-INTA), Departamento de Astrofísica Molecular, Ctra. de Aljalvir Km 4, 28850 Torrejón de Ardoz, Madrid, Spain e-mail: [belen;pardo]@damir.iem.csic.es; [jcernicharo;jr.goicoechea]@cab.inta-csic.es Received 19 October 2009 / Accepted 15 April 2010 ABSTRACT We perform a sensitive (line confusion limited), single-side band spectral survey towards Orion KL with the IRAM 30 m telescope, covering the following frequency ranges: 80-115.5 GHz, 130-178 GHz, and 197-281 GHz. We detect more than 14 400 spectral features of which 10 040 have been identified up to date and attributed to 43 different molecules, including 148 isotopologues and lines from vibrationally excited states. In this paper, we focus on the study of OCS, HCS + ,H 2 CS, CS, CCS, C 3 S, and their isotopologues. In addition, we map the OCS J = 18-17 line and complete complementary observations of several OCS lines at selected positions around Orion IRc2 (the position selected for the survey). We report the first detection of OCS ν 2 = 1 and ν 3 = 1 vibrationally excited states in space and the first detection of C 3 S in warm clouds. Most of CCS, and almost all C 3 S, line emission arises from the hot core indicating an enhancement of their abundances in warm and dense gas. Column densities and isotopic ratios have been calculated using a large velocity gradient (LVG) excitation and radiative transfer code (for the low density gas components) and a local thermal equilibrium (LTE) code (appropriate for the warm and dense hot core component), which takes into account the different cloud components known to exist towards Orion KL, the extended ridge, compact ridge, plateau, and hot core. The vibrational temperature derived from OCS ν 2 = 1 and ν 3 = 1 levels is ≃210 K, similar to the gas kinetic temperature in the hot core. These OCS high energy levels are probably pumped by absorption of IR dust photons. We derive an upper limit to the OC 3 S, H 2 CCS, HNCS, HOCS + , and NCS column densities. Finally, we discuss the D/H abundance ratio and infer the following isotopic abundances: 12 C/ 13 C = 45 ± 20, 32 S/ 34 S = 20 ± 6, 32 S/ 33 S = 75 ± 29, and 16 O/ 18 O = 250 ± 135. Key words. surveys – stars: formation – ISM: abundances – ISM: clouds – ISM: molecules – radio lines: ISM 1. Introduction The Orion KL (Kleinmann-Low) cloud is the closest (≃414 pc, Menten et al. 2007) and most well studied high mass star- forming region in our Galaxy (see, e. g., Genzel & Stutzki 1989 for review). The prevailing chemistry of the cloud is particularly complex as a result of the interaction of the newly formed pro- tostars, outflows, and their environment. The evaporation of dust mantles and the high gas temperatures produce a wide variety of molecules in the gas phase that are responsible for a spectacu- larly prolific and intense line spectrum (Blake et al. 1987; Brown et al. 1988; Charnley 1997). Near- and mid-IR subarcsecond resolution imaging and (sub)millimeter interferometric observations have identified the main sources of luminosity, heating, and dynamics in the re- gion. At first, IRc2 was believed to be the responsible for this complex environment. However, the 8-12 μm emission peak of IRc2 is not coincident with the the origin of the outflow(s) (and the Orion SiO maser origin), and its intrinsic IR luminos- ity (L ≈ 1000 L ⊙ ) is only a fraction of the luminosity of the entire system (Gezari et al. 1998). In addition, 3.6-22 μm im- ages indicate that IRc2 is resolved into four non self-luminous components. Therefore, IRc2 is not presently the powerful en- gine of Orion KL and its nature remains unclear (Dougados et al. 1993; Shuping et al. 2004; Greenhill et al. 2004). ⋆ Appendices A and B are only available in electronic form at http://www.aanda.org Menten & Reid (1995) identified the very embedded radio continuum source I (a young star with a very high luminos- ity without an infrared counterpart, ≃10 5 L ⊙ , Gezari et al. 1998; Greenhill et al. 2004, located 0. ′′ 5 south of IRc2) as the source coinciding with the centroid of the SiO maser distribu- tion (Plambeck et al. 2009; Zapata et al. 2009a; Goddi et al. 2009b). They also detected the radio continuum emission of IR source n, suggesting this source as another precursor of the large- scale phenomena. In addition, Beuther et al. (2004) detected a sub-millimeter source without IR and centimeter counterparts, SMA1, previously predicted by de Vicente et al. (2002), which may be the source driving the high velocity outflow (Beuther & Nissen 2008). Thus, the core of Orion KL contains the compact HII regions I and n (in addition to BN, which was resolved with high resolution at 7 mm by Rodríguez et al. 2009), which appear to be receding from a common point, an originally massive stel- lar system that disintegrated ≃500 years ago (Gómez et al. 2005; Zapata et al. 2009b). Finally, submm aperture synthesis line sur- veys provided the spatial location and extent of many molecular species (Blake et al. 1996; Wright et al. 1996; Liu et al. 2002; Beuther et al. 2005; Goddi et al. 2009b; Plambeck et al. 2009; Zapata et al. 2009a). The chemical complexity of Orion KL has been demon- strated by several line surveys performed at different fre- quency ranges: 72.2-91.1 GHz by Johansson et al. (1984); 215-247 GHz by Sutton et al. (1985); 247-263 GHz by Blake et al. (1986); 200.7-202.3, 203.7-205.3 and 330-360 GHz by Jewell et al. (1989); 70-115 GHz by Turner (1989); Article published by EDP Sciences Page 1 of 37