A line confusion-limited millimeter survey of Orion KL

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 SO 2 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. = 1 and for several undetected sulfur-bearing species. In addition, we present 2 × 2 maps around Orion IRc2 of SO 2 transitions with energies from 19 to 131 K and also maps with four transitions of SO, 34 SO, and 34 SO 2 . 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 SO 2 . 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 SO 2 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 SO 2 are good tracers, not only of regions affected by shocks, but also of regions with warm dense gas (hot cores).

Modelling the sulphur chemistry evolution in Orion KL

“…As a result, the SO 2 /SO ratio increases with time, in agreement with the results obtained by Wakelam et al (2011), who modelled the sulphur chemistry of several massive dense cores. This is also consistent with Esplugues et al (2013a), who concluded that SO 2 is a better tracer of warm gas than SO. For longer times, t 8 × 10 4 years since the star switches on, the increase in SO 2 starts to be limited as the reaction…”

Combined IRAM andHerschel/HIFI study of cyano(di)acetylene in Orion KL: tentative detection of DC3N

“…To obtain a good fit to the lines at low frequencies, we also considered a contribution from the extended ridge, with a column density of N(HC 3 N) = (8 ± 2) × 10 13 cm −2 . In addition, similar to the analysis of SO and SO 2 emission in Esplugues et al (2013), we also found a contribution from the component centered at 20.5 km s −1 , with N(HC 3 N) = (3.4 ± 0.6) × 10 14 cm −2 . This contribution is negligible in the isotopologues or vibrational modes of HC 3 N, but it is significant for ground-state transitions, as we can see in the line profiles in Fig.…”

“…To apply the LVG code, we considered the same cloud components for Orion KL as were used in Esplugues et al (2013) for the analysis of SO and SO 2 . Most of these cloud components were also considered in previous Orion KL interferometric studies such as those of Wright et al (1996) and Beuther et al (2005).…”

“…5) of the line profiles of HC 3 N, we assumed uniform physical conditions of density, kinetic temperature, line width, and radial velocity for each component (see Table 4), so that the column density of each observed species is the only free parameter. However, to fit the line profiles of HC 3 N (ground and vibrational states) obtained with Herschel observations, a density and temperature stratification or gradient in the hot core is needed (as was predicted by Esplugues et al (2013) with IRAM observations of SO 2 transitions with high energies, >700 K). This gradient was simulated by adding a hotter inner component to the typical hot core conditions (see Table 4).…”

Millimetre spectral line mapping observations towards four massive star-forming H ii regions

“…The millimetre wavelength window is important for studying massive star formation, because it contains many useful molecular probes, such as shock tracers (SiO, SO, HNCO and H 2 CO; Schilke et al 1997;Esplugues et al 2013;Rizzo, Fuente & García-Burillo 2005), long carbon chain molecules (c-C 3 H 2 , HC 3 N and HC 5 N; Morris, Snell & vanden Bout 1977;Chung, Osamu & Masaki 1991;Bergin, Snell & Goldsmith 1996), deuterated molecules (DCN, DCO + , C 2 D and NH 2 D; Shah & Wootten 2001;Pety et al 2007;Parise et al 2009) and dense gas traces (HCN, HCO + , CS and C 2 H; Padovani et al 2009), etc.…”