Resolving the chemical substructure of Orion-KL

Abstract

Context. The Kleinmann-Low nebula in Orion (Orion-KL) is the nearest example of a high-mass star-forming environment. Studying the resolved chemical substructures of this complex region provides important insight into the chemistry of high-mass star-forming regions (HMSFRs), as it relates to their evolutionary states. Aims. The goal of this work is to resolve the molecular line emission from individual substructures of Orion-KL at high spectral and spatial resolution and to infer the chemical properties of the associated gas.Methods. We present a line survey of Orion-KL obtained from combined Submillimeter Array (SMA) interferometric and IRAM 30 m single-dish observations. Covering a 4 GHz bandwidth in total, this survey contains over 160 emission lines from 20 species (25 isotopologues), including 11 complex organic molecules (COMs). Spectra are extracted from individual substructures and the intensity-integrated distribution map for each species is provided. We then estimate the rotation temperature for each substructure, along with their molecular column densities and abundances. Results. For the first time, we complement 1.3 mm interferometric data with single-dish observations of the Orion-KL region and study small-scale chemical variations in this region. (1) We resolve continuum substructures on ∼3 angular scale. (2) We identify lines from the low-abundance COMs CH 3 COCH 3 and CH 3 CH 2 OH, as well as tentatively detect CH 3 CHO and long carbon-chain molecules C 6 H and HC 7 N. (3) We find that while most COMs are segregated by type, peaking either towards the hotcore (e.g., nitrogenbearing species) or the compact ridge (e.g., oxygen-bearing species like HCOOCH 3 and CH 3 OCH 3 ), the distributions of others do not follow this segregated structure (e.g., CH 3 CH 2 OH, CH 3 OH, CH 3 COCH 3 ). (4) We find a second velocity component of HNCO, SO 2 , 34 SO 2 , and SO lines, which may be associated with a strong shock event in the low-velocity outflow. (5) Temperatures and molecular abundances show large gradients between central condensations and the outflow regions, illustrating a transition between hot molecular core and shock-chemistry dominated regimes. Conclusions. Our observations of spatially resolved abundance variations in Orion-KL provide the nearest reference source for hot molecular core and outflow chemistry, which will be an important example for interpreting the chemistry of more distant HMSFRs.

The complexity of Orion: an ALMA view

“…As previously noted by several authors (e.g. Feng et al 2015;Peng et al 2017), these excited modes are mostly situated in the northern part of the region (Fig. 9).…”

“…The LTE fit was performed using LINEDB and WEEDS sets of routines inside CLASS (Maret et al 2011). The line catalogues are the Cologne Database for Molecular Spectroscopy (CDMS, Müller et al 2001Müller et al , 2005 and the Jet Propulsion Laboratory (JPL) catalogue (Pickett et al 1998), with some complementary data provided by A. Belloche from the Belloche et al (2013, hereafter B13) work to identify vibrationally excited states of vinyl and ethyl cyanides which we do not discuss in this paper but which were needed since a number of these transitions are very strong, up to 30 K. Rieke et al (1973), Shuping et al (2004), mmxx from Feng et al (2015) and references therein. The yellow cross indicates the center of explosion from which the BN, I, and n sources (marked by yellow stars) are moving away (Gómez et al 2005 …”

“…Hexatriynyl C 6 H Feng et al (2015) report the tentative detection of hexatriynyl, C 6 H, a precursor of the C 6 H − anion. They indicate that the only unblended line in their survey appears at 230.109 GHz towards their SMA1 source, 0 .…”

“…In two recent papers (Feng et al 2015;Liseau & Larsson 2015) a tentative detection of three species has been reported. We do not confirm these detections, as discussed below.…”

“…Naturally, interferometers have been used to separate the components, diminish the confusion, and help understand the ongoing evolution of the chemical and physical complex structure (e.g. Favre et al 2011a;Peng et al 2012Peng et al , 2017Brouillet et al 2013;Feng et al 2015;Tercero et al 2015).…”