A line-confusion limited millimeter survey of Orion KL

Abstract

Aims. We present a study of the silicon-bearing species detected in a line-confusion limited survey towards Orion KL performed with the IRAM 30-m telescope. The analysis of the line survey is organized by families of molecules. Our aim is to derive physical and chemical conditions for each family taking all observed lines into account from all isotopologs of each species. The large number of transitions in different vibrationally excited states covered by our data, which range from 80 to 280 GHz, let us provide reliable source-average column densities (hence, isotopolog abundances and vibrational temperatures) for the detected molecules. In addition, we provide a wide study of the physical properties of the source based on the different spectral components found in the emission lines. Methods. We modeled the lines of the detected molecules using a radiative transfer code, which permit us to choose between large velocity gradient (LVG) and local thermodynamic equilibrium (LTE) approximations depending on the physical conditions of the gas. We used appropriate collisional rates for the LVG calculations. To qualitatively investigate the origin of the SiS and SiO emissions in Orion KL we ran a grid of chemical models.Results. For the v = 1 state of SiO, we detected the J = 2−1 line and, for the first time in this source, emission in the J = 4−3 transition, both of them showing a strong masering effect. For SiO v = 0, we detected 28 SiO, 29 SiO, and 30 SiO; in addition, we have mapped the J = 5−4 SiO line. For SiS, we have detected the main species, 29 SiS, and SiS v = 1. Unlikely other species detected in Orion KL (IRc2), the emission peak of SiS appears at a velocity of 15.5 km s −1 . A study of the 5−4 SiO line around IRc2 shows this feature as an extended component that probably arises from the interaction of the outflow with the ambient cloud. We derive an SiO/SiS column density ratio of 13 in the plateau component, four times lower than the cosmic O/S ratio 48. In addition, we provide upper limits to the column density of several non-detected silicon-bearing species. The results of our chemical models show that while it is possible to reproduce SiO in the gas phase (as well as on the grains), SiS is a product of surface reactions, most likely involving direct reactions of sulfur with silicon.

Outflow structure and velocity field of Orion source

“…Consistently, Tercero et al (2011) showed that the 29 SiO v = 0 J = 5-4 line is contaminated by the following molecules: the hydrogen-sulfide isotopologue 34 SH 2 , the methyl-cyanide isotopologue 13 CH 3 CN, and sulfur-monoxide (SO). Beuther et al (2005) imaged the (19 6,19 -18 6,18 ) 13 CH 3 CN line at 339 137 GHz, which clearly peaks both at the hot core and IRc7 positions.…”

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

“…But especially interesting is the obtained D/H ratio (0.015), which is similar to that for dark clouds, like the ratio obtained by Langer et al (1980) in TMC1, D/H = 0.02−0.08. Table 8 shows the derived molecular abundances of HC 3 N, HC 5 N, and DC 3 N with respect to hydrogen in each component (see Tercero et al (2011) for the assumed values of N H 2 ). We found that the highest abundance of HC 3 N is obtained in the high-velocity plateau, whereas in the hot core this abundance is twice as low.…”

Microwave and submillimeter spectroscopy and first ISM detection of18O-methyl formate

“…Thanks to the new laboratory frequencies provided above, we have detected the two 18 O isotopologues of HCOOCH 3 in the IRAM 30 m line survey of Orion KL presented in Tercero et al (2010Tercero et al ( , 2011. After summarizing the observations, data reduction, and overall results of that line survey (Sect.…”

“…These components are characterized by different physical and chemical conditions (Blake et al 1987;Blake et al 1996;Tercero et al 2010Tercero et al , 2011: (i) a narrow or "spike" (∼4 km s −1 line-width) component at v LSR 9 km s −1 delineating a north-to-south extended ridge or ambient cloud (T k 60 K, n(H 2 ) 10 5 cm −3 ); (ii) a compact and quiescent region, the compact ridge, (v LSR 8 km s −1 , Δv 3 km s −1 , T k 110 K, n(H 2 ) 10 6 cm −3 ) identified for the first time by Johansson et al (1984); (iii) the plateau, a mixture of outflows, shocks, and interactions with the ambient cloud (v LSR 6−10 km s −1 , Δv 25 km s −1 , T k 150 K, n(H 2 ) 10 6 cm −3 ); (iv) a hot core component (v LSR 5 km s −1 , Δv ∼ 10 km s −1 , T k 225 K, n(H 2 ) 5 × 10 7 cm −3 ) first detected in ammonia emission Morris et al (1980). Methyl formate (in general, organic saturated O-rich molecules) emission comes mainly from the compact ridge component.…”

“…6.1). We adopted these values from the data analysis (Gaussian fits and an attempt to simulate the line profiles for several molecules with LTE and LVG codes in that line survey, see Tercero et al 2010Tercero et al , 2011 as representative parameters for the different cloud components. Our modelling technique also took into account the size of each component and its offset position with respect to IRc2.…”