Heterodyne Array Receiver Research Articles

Magnetic fields under feedback: a case study of the massive star-forming hub G34.26 + 0.15

ABSTRACT We present 850 $\mu$m polarized observations of the molecular cloud G34.26 + 0.15 taken using the POL-2 polarimeter mounted on the James Clerk Maxwell Telescope (JCMT). G34.26 + 0.15 is a hub–filament system with ongoing high-mass star formation, containing multiple H ii regions. We extend the histogram of relative orientations technique with an alternative application that considers the alignment of the magnetic field to the filaments and a H ii region boundary, denoted as the filament alignment factor ($\xi _{F}$) and the ellipse alignment factor ($\xi _{E}$), respectively. Using these metrics, we find that, although in general the magnetic field aligns parallel to the filamentary structure within the system in the north-west, the magnetic field structure of G34.26 + 0.15 has been radically reshaped by the expansion of an evolved H ii region in the south-east, which itself may have triggered further high-mass star formation in the cloud. Thus, we suggest high-mass star formation is occurring through both mass accretion as per the hub–filament model from one side and compression of gas under stellar feedback from the other. We also use HARP (Heterodyne Array Receiver Program) observations of C$^{18}$O from the CHIMPS survey to estimate the magnetic field strength across the cloud, finding strengths of $\sim$0.5–1.4 mG.

The Formation of Filaments and Dense Cores in the Cocoon Nebula (IC 5146)

We present 850 μm linear polarization and C18O (3 − 2) and 13CO (3 − 2) molecular line observations toward the filaments (F13 and F13S) in the Cocoon Nebula (IC 5146) using the JCMT POL-2 and Heterodyne Array Receiver Program instruments. F13 and F13S are found to be thermally supercritical with identified dense cores along their crests. Our findings include that the polarization fraction decreases in denser regions, indicating reduced dust grain alignment efficiency. The magnetic field vectors at core scales tend to be parallel to the filaments, but disturbed at the high density regions. Magnetic field strengths measured using the Davis–Chandrasekhar–Fermi method are 58 ± 31 and 40 ± 9 μG for F13 and F13S, respectively, and it reveals subcritical and sub-Alfvénic filaments, emphasizing the importance of magnetic fields in the Cocoon region. Sinusoidal C18O (3 − 2) velocity and density distributions are observed along the filaments’ skeletons, and their variations are mostly displaced by ∼1/4 × the wavelength of the sinusoid, indicating core formation occurred through the fragmentation of a gravitationally unstable filament, but with shorter core spacings than predicted. Large-scale velocity fields of F13 and F13S, studied using 13CO (3 − 2) data, present a V-shape transverse velocity structure. We propose a scenario for the formation and evolution of F13 and F13S, along with the dense cores within them. A radiation shock front generated by a B-type star collided with a sheet-like cloud about 1.4 Myr ago. The filaments became thermally critical due to mass infall through self-gravity ∼1 Myr ago, and subsequently, dense cores formed through gravitational fragmentation, accompanied by the disturbance of the magnetic field.

Design of boadband THz multi-beam splitting metasurface

Generating multiple local oscillator (LO) beams by beam splitters is a crucial aspect of large heterodyne array receivers operating at terahertz (THz) frequencies, with over 100 pixels. Metasurfaces have received considerable attention due to their unique and flexible wavefront modulation capabilities. Nevertheless, the design of beam-splitting metasurfaces faces significant challenges in increasing the number of diffraction beams, improving power efficiency, and achieving greater homogeneity. A SA-GS-based design model for beam-splitting metasurfaces is proposed to achieve multi-beam with high power efficiency and homogeneity. As a proof of concept, we have designed and optimized a 16-beam splitting metasurface from 0.82 THz to 1.6 THz. The objective is to develop large-pixel THz multi-beam heterodyne array receivers and optical systems. The number of beams is also extended to 100-, 144-, 225-, and 289-beam configurations, with power efficiencies of 93.55%, 93.92%, 96.01%, and 96.18% at 0.85 THz, respectively. Moreover, the main beams exhibit excellent homogeneity. This model can be employed in the design of multi-beam metasurfaces with variable deflection angles and intensity ratios. Finally, the multi-beam splitting metasurface is fabricated, and the experimental measurement agrees with the simulation. This work presents an effective approach for the inverse design of beam splitters or holographic imaging devices.

Dual-wavelength terahertz two-dimensional phase gratings based on all dielectric metasurfaces

Efficient and accurate phase gratings hold immense significance in the realization of large format heterodyne array receivers at terahertz frequencies. Metallic phase gratings have made substantial advancements in terms of operating wavelength and the number of diffraction beams. Like most other diffractive optical devices, metallic phase gratings are primarily optimized to operate at one specific wavelength. Metasurfaces compositing arrays of subwavelength nanostructures have been demonstrated with various optical functions, by freely modifying the polarization, phase, and amplitude of light. In this study, we present an approach to create a multi-wavelength phase grating compositing segments that incorporate multiple nanostructures. The resulting transmission phase grating not only exhibits uniform diffraction beams (2 × 2) but also achieves the same diffraction angles at both 1.31 and 2.7 THz. The measured total power efficiency of the diffraction beam pattern is 53.2% for 1.31 THz and 42.4% for 2.7 THz. These devices can be applied in terahertz astronomical observations and fluorescence microscopy applications, where multi-wavelength operation is necessary.

Development of Through-Substrate via Process for Silicon-Based Monolithic Microwave Integrated Circuits SIS Mixer

We designed and fabricated superconducting monolithic microwave integrated circuits (MMICs) at 2 mm wavelengths. Balanced superconductor-insulator-superconductor (SIS) mixers and silicon membrane-based planar orthomode transducers are incorporated into the MMICs, which is used to develop compact heterodyne array receivers for radio astronomical observations. Because of substrate cavity modes, crosstalk between the outputs of balanced mixers was observed at intermediate frequencies, which deteriorated the noise rejection ratio. Three-dimensional electromagnetic simulation proved that the cavity modes can be effectively suppressed by introducing conducting through-substrate vias (TSVs). We have been developing a TSV fabrication process compatible with that for the superconducting MMICs containing silicon membranes by using non-Bosch deep silicon etching and using sputtered Nb films. The fabricated TSVs were characterized by scanning electron microscopy and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> measurement.

Beam Waist Properties of Spiral Antenna Coupled HEB Mixers at Supra-THz Frequencies

We have simulated and measured the beam properties of lens-antenna coupled hot electron bolometer mixers at a few supra-terahertz frequencies between 1.4 and 5.3 THz. The quasi-optical structures consist of an elliptical lens and a logarithmic spiral antenna. The model used for our simulations consists of a finite-element analysis to simulate the far-field radiation pattern of the antenna, geometrical optics to map the antenna radiation to the lens surface, and physical optics to calculate an arbitrary far field. We perform a thorough study of the beam properties, such as beam waist radius, phase center location and axial ratio by varying the diameter and extension of the lens, and misalignments of the antenna relative to the lens, at different operating frequencies. The simulation results are applied to the design and optimization of three different lenses for mixers to be operated at 1.4, 1.9, and 4.7 THz, respectively, which will be used in the heterodyne array receivers on board of NASA's balloon borne GUSTO observatory. The beam properties were verified experimentally by measuring the beam patterns in amplitude at multiple planes using a heterodyne technique. We found that the experimental results show good agreement with those from the simulations. Our work has delivered the mixers with the required beam characteristics for GUSTO.

12CO (3–2) High-Resolution Survey (COHRS) of the Galactic Plane: Complete Data Release

We present the full data release of the 12CO (3–2) High-Resolution Survey (COHRS), which has mapped the inner Galactic plane over the range of 9.°5 ≤ l ≤ 62.°3 and ∣b∣ ≤ 0.°5. COHRS has been carried out using the Heterodyne Array Receiver Program on the 15 m James Clerk Maxwell Telescope in Hawaii. The released data are smoothed to have a spatial resolution of 16.″6 and a velocity resolution of 0.635 km s−1, achieving a mean rms of ∼0.6 K on . The COHRS data are useful for investigating detailed three-dimensional structures of individual molecular clouds and large-scale structures such as spiral arms in the Galactic plane. Furthermore, data from other available public surveys of different CO isotopologues and transitions with similar angular resolutions to this survey, such as FUGIN, SEDIGISM, and CHIMPS/CHIMPS2, allow studies of the physical properties of molecular clouds and comparison of their states. In this paper, we report further observations on the second release and improved data reduction since the original COHRS release. We discuss the characteristics of the COHRS data and present integrated-emission images and a position–velocity (PV) map of the region covered. The PV map shows a good match with spiral-arm traces from existing CO and H i surveys. We also obtain and compare integrated one-dimensional distributions of 12CO (1–0) and (3–2) and those of star-forming populations.

Broadband terahertz multi-beam splitters with uniform power distribution based on coding metasurfaces

High efficiency, uniform power distribution, and broadband working of beam splitters are of crucial importance for large format heterodyne array receivers at terahertz frequencies. We present two types of quad-beam splitters (QBSs) based on coding metamaterials, designed to generate 1 × 4 and 2 × 2 beams respectively in the THz range. The designed metasurfaces are composed of a periodic array of metal-dielectric-metal (MDM) scattering unit cells, thus introducing a well-designed phase shift in the electromagnetic wave. For normally incident electromagnetic waves, the simulation results show that the 2 × 2 QBS has higher power efficiency and broader bandwidth in comparison with the 1 × 4 QBS. The 2 × 2 QBS works well in that the power efficiency is larger than 70% and the power distribution difference of the main beams is less than 2.8% in the range of 0.75–1.35 THz, which indicates an ultra-broad frequency range up to 57.1%. Meanwhile, under oblique incidence, the power distribution and the power efficiency among the 2 × 2 quad-beam nearly remain stable when the wave incident is within 40-degree. A prototype is fabricated and the 2 × 2 QBS behavior is experimentally demonstrated at 0.85 THz, where the power efficiency is as high as 70.4% and the power distribution of each beam approximately is uniform under the 20-degree incidence. To further improve the efficiency of astronomical observations, a 36-beam splitter is designed by using a simple two-dimensional addition method, and the power efficiency can reach 89.9% at 0.85 THz, and the working bandwidth is 57.1% from 0.75 to 1.35 THz with evenly distributed main beams. The simulation results show that the beam splitting function can also be well realized under the waves with 20-degree oblique incidence. Compared to conventional Fourier phase gratings, the metasurface-based beam splitters provide broadband performance and a simpler fabrication process, which is very expected in compact heterodyne array receiver systems.

Observation and calibration strategies for large-scale multi-beam velocity-resolved mapping of the [CII] emission in the Orion molecular cloud

Context.The [CII] 158 μm far-infrared fine-structure line is one of the dominant cooling lines of the star-forming interstellar medium. Hence [CII] emission originates in and thus can be used to trace a range of ISM processes. Velocity-resolved large-scale mapping of [CII] in star-forming regions provides a unique perspective of the kinematics of these regions and their interactions with the exciting source of radiation.Aims.We explore the scientific applications of large-scale mapping of velocity-resolved [CII] observations. With the [CII] observations, we investigate the effect of stellar feedback on the ISM. We present the details of observation, calibration, and data reduction using a heterodyne array receiver mounted on an airborne observatory.Methods.A 1.15 square degree velocity-resolved map of the Orion molecular cloud centred on the bar region was observed using the German REceiver for Astronomy at Terahertz Frequencies (upGREAT) heterodyne receiver flying on board the Stratospheric Observatory for Infrared Astronomy. The data were acquired using the 14 pixels of the German REceiver for Astronomy at Terahertz Frequencies that were observed in an on-the-fly mapping mode. 2.4 million spectra were taken in total. These spectra were gridded into a three-dimensional cube with a spatial resolution of 14.1 arcseconds and a spectral resolution of 0.3 km s−1.Results.A square-degree [CII] map with a spectral resolution of 0.3 km s−1is presented. The scientific potential of this data is summarized with discussion of mechanical and radiative stellar feedback, filament tracing using [CII], [CII] opacity effects, [CII] and carbon recombination lines, and [CII] interaction with the large molecular cloud. The data quality and calibration is discussed in detail, and new techniques are presented to mitigate the effects of unavoidable instrument deficiencies (e.g. baseline stability) and thus to improve the data quality. A comparison with a smaller [CII] map taken with theHerschel/Heterodyne Instrument for the Far-Infrared spectrometer is presented.Conclusions.Large-scale [CII] mapping provides new insight into the kinematics of the ISM. The interaction between massive stars and the ISM is probed through [CII] observations. Spectrally resolving the [CII] emission is necessary to probe the microphysics induced by the feedback of massive stars. We show that certain heterodyne instrument data quality issues can be resolved using a spline-based technique, and better data correction routines allow for more efficient observing strategies.

Development of terahertz two-dimensional phase gratings for multiple beam generation based on a high-accuracy phase retrieval algorithm.

High efficiency and accuracy phase gratings are of crucial importance for large format heterodyne array receivers at terahertz frequencies. Here, by developing a design approach that can create gratings with arbitrary two-dimensional diffraction distributions, we have realized a reflective metallic phase grating that generates 2×2 diffraction beams at 0.85 THz. The measured total power efficiency of the diffraction beam pattern is 81.9%, which demonstrates at least 17% improvement in efficiency compared with the standard pseudo-2D Fourier phase grating. In addition, we report the realization of up to 10×10 diffraction beam two-dimensional phase grating designs at terahertz wavelengths, using an adaptation of the Gerchberg-Saxton (GS) scheme known as the Mixed-Region-Amplitude-Freedom algorithm. Rigorous full wave simulation proves the efficiency and accuracy of the design, which overcomes the inaccurate intensity of the beam distribution drawbacks originated from the standard GS algorithm. The results pave the way for the development of large-pixel terahertz multi-beam heterodyne receivers.

Heterodyne Receiver for Origins

The Heterodyne Receiver for Origins (HERO) is the first detailed study of a heterodyne focal plane array receiver for space applications. HERO gives the Origins Space Telescope the capability to observe at very high spectral resolution (R = 107) over an unprecedentedly large far-infrared (FIR) wavelengths range (111 to 617 μm) with high sensitivity, with simultaneous dual polarization and dual-frequency band operation. The design is based on prior successful heterodyne receivers, such as Heterodyne Instrument for the Far-Infrared /Herschel, but surpasses it by one to two orders of magnitude by exploiting the latest technological developments. Innovative components are used to keep the required satellite resources low and thus allowing for the first time a convincing design of a large format heterodyne array receiver for space. HERO on Origins is a unique tool to explore the FIR universe and extends the enormous potential of submillimeter astronomical spectroscopy into new areas of astronomical research.

CHIMPS2: survey description and 12CO emission in the Galactic Centre

ABSTRACT The latest generation of Galactic Plane surveys is enhancing our ability to study the effects of galactic environment upon the process of star formation. We present the first data from CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). CHIMPS2 is a survey that will observe the Inner Galaxy, the Central Molecular Zone (CMZ), and a section of the Outer Galaxy in 12CO, 13CO, and C18O $(J = 3\rightarrow 2)$ emission with the Heterodyne Array Receiver Program on the James Clerk Maxwell Telescope (JCMT). The first CHIMPS2 data presented here are a first look towards the CMZ in 12CO J = 3 → 2 and cover ${-}3^{\circ }\, \le \, \ell \, \le \, 5^{\circ }$ and $\mid {b} \mid \, \le \, 0{_{.}^{\circ}} 5$ with angular resolution of 15 arcsec, velocity resolution of 1 km s−1, and rms $\Delta \, T_A ^\ast =$ 0.58 K at these resolutions. Such high-resolution observations of the CMZ will be a valuable data set for future studies, whilst complementing the existing Galactic Plane surveys, such as SEDIGISM, the ${Herschel}$ infrared Galactic Plane Survey, and ATLASGAL. In this paper, we discuss the survey plan, the current observations and data, as well as presenting position–position maps of the region. The position–velocity maps detect foreground spiral arms in both absorption and emission.

The upGREAT Dual Frequency Heterodyne Arrays for SOFIA

We present the performance of the upGREAT heterodyne array receivers on the SOFIA telescope after several years of operations. This instrument is a multi-pixel high resolution ([Formula: see text]) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receivers use 7-pixel subarrays configured in a hexagonal layout around a central pixel. The low frequency array receiver (LFA) has [Formula: see text] pixels (dual polarization), and presently covers the 1.83–2.07[Formula: see text]THz frequency range, which allows to observe the [CII] and [OI] lines at 158[Formula: see text][Formula: see text]m and 145[Formula: see text][Formula: see text]m wavelengths. The high frequency array (HFA) covers the [OI] line at 63[Formula: see text][Formula: see text]m and is equipped with one polarization at the moment (7 pixels, which can be upgraded in the near future with a second polarization array). The 4.7[Formula: see text]THz array has successfully flown using two separate quantum-cascade laser local oscillators from two different groups. NASA completed the development, integration and testing of a dual-channel closed-cycle cryocooler system, with two independently operable He compressors, aboard SOFIA in early 2017 and since then, both arrays can be operated in parallel using a frequency separating dichroic mirror. This configuration is now the prime GREAT configuration and has been added to SOFIA’s instrument suite since observing cycle 6.

CHIMPS: the13CO/C18O (J = 3 → 2) Heterodyne Inner Milky Way Plane Survey

We present the $^{13}$CO/C$^{18}$O (J=3-2) Heterodyne Inner Milky Way Plane Survey (CHIMPS) which has been carried out using the Heterodyne Array Receiver Program on the 15 m James Clerk Maxwell Telescope (JCMT) in Hawaii. The high-resolution spectral survey currently covers |b| < 0.5 deg and 28 < l < 46 deg, with an angular resolution of 15 arcsec in 0.5 km/s velocity channels. The spectra have a median rms of $\sim$ 0.6 K at this resolution, and for optically thin gas at an excitation temperature of 10 K, this sensitivity corresponds to column densities of $N_{\mathrm{H}_{2}} \sim 3 \times 10^{20}\,$cm$^{-2}$ and $N_{\mathrm{H}_{2}} \sim 4 \times 10^{21}\,$cm$^{-2}$ for $^{13}$CO and C$^{18}$O, respectively. The molecular gas that CHIMPS traces is at higher column densities and is also more optically thin than in other publicly available CO surveys due to its rarer isotopologues, and thus more representative of the three-dimensional structure of the clouds. The critical density of the J=3-2 transition of CO is $\gtrsim 10^{4}$ cm$^{-3}$ at temperatures of $\leq 20$ K, and so the higher density gas associated with star formation is well traced. These data complement other existing Galactic plane surveys, especially the JCMT Galactic Plane Survey which has similar spatial resolution and column density sensitivity, and the Herschel infrared Galactic Plane Survey. In this paper, we discuss the observations, data reduction and characteristics of the survey, presenting integrated emission maps for the region covered. Position-velocity diagrams allow comparison with Galactic structure models of the Milky Way, and while we find good agreement with a particular four arm model, there are some significant deviations.

Terahertz Heterodyne Array Receivers for Astronomy

We review the development of multi-pixel heterodyne receivers for astronomical research in the submillimeter and terahertz spectral domains. We shortly address the historical development, highlighting a few pioneering instruments. A discussion of the design concepts is followed by a presentation of the technologies employed in the various receiver subsystems and of the approaches taken to optimize these for current and future instruments.

CO (3 – 2) HIGH-RESOLUTION SURVEY OF THE GALACTIC PLANE: R1

We present the first release (R1) of data from the CO High-Resolution Survey (COHRS), which maps a strip of the inner Galactic plane in 12CO?(J = 3 ? 2). The data are taken using the Heterodyne Array Receiver Programme on the James Clerk Maxwell Telescope (JCMT) in Hawaii, which has a 14?arcsec angular resolution at this frequency. When complete, this survey will cover |b| ? 0.?5 between 10? < l < 65?. This first release covers |b| ? 0.?5 between 10.?25 < l < 17.?5 and 50.?25 < l < 55.?25, and |b| ? 0.?25 between 17.?5 < l < 50.?25. The data are smoothed to a velocity resolution of 1?km?s?1, a spatial resolution of 16?arcsec and achieve a mean rms of ~1?K. COHRS data are available to the community online at http://dx.doi.org/10.11570/13.0002. In this paper we describe the data acquisition and reduction techniques used and present integrated intensity images and longitude-velocity maps. We also discuss the noise characteristics of the data. The high resolution is a powerful tool for morphological studies of bubbles and filaments while the velocity information shows the spiral arms and outflows. These data are intended to complement both existing and upcoming surveys, e.g., the Bolocam Galactic Plane Survey (BGPS), ATLASGAL, the Herschel Galactic Plane Survey (Hi-GAL) and the JCMT Galactic Plane Survey with SCUBA-2 (JPS).

Characterization of Imperfections in a Martin-Puplett Interferometer Using Ray-Tracing

The effects of imperfections of quasioptical components due to misalignment and manufacturing accuracy on optical path lengths in a Martin-Puplett interferometer have been studied with ray-tracing simulations. Optical path lengths in a test interferometer have been measured and then reproduced as accurately as possible in a simulation by introducing several parameters describing the imperfections. The measurements of a polarizer frame, the profile of a roof mirror and the effect of mirror tilting provide support for the existence of the simulated imperfections. The method has been applied also to the diplexer of the heterodyne array receiver CHAMP+, operated by the Max Planck Institute for Radio Astronomy at the APEX telescope, to gain insights on how to improve the performance of the receiver.

Molecular clumps in the W51 giant molecular cloud

In this paper, we present a catalogue of dense molecular clumps located within the W51 giant molecular cloud (GMC). This work is based on Heterodyne Array Receiver Programme 13CO J = 3–2 observations of the W51 GMC and uses the automated CLUMPFIND algorithm to decompose the region into a total of 1575 clumps of which 1130 are associated with the W51 GMC. We clearly see the distinct structures of the W51 complex and the high-velocity stream previously reported. We find the clumps have characteristic diameters of 1.4 pc, excitation temperatures of 12 K, densities of 5.6 × 1021 cm−2, surface densities 0.02 g cm−2 and masses of 90 M⊙. We find a total mass of dense clumps within the GMC of 1.5 × 105 M⊙, with only 1 per cent of the clumps detected by number and 4 per cent by mass found to be supercritical. We find a clump-forming efficiency of 14 ± 1 per cent for the W51 GMC and a supercritical clump-forming efficiency of per cent. Looking at the clump mass distribution, we find it is described by a single power law with a slope of above ∼100 M⊙. By comparing locations of supercritical clumps and young clusters, we see that any future star formation is likely to be located away from the currently active W51A region.

CO depletion in the Gould Belt clouds

We present a statistical comparison of CO depletion in a set of local molecular clouds within the Gould Belt using Sub-millimetre Common User Bolometer Array (SCUBA) and Heterodyne Array Receiver Programme (HARP) data. This is the most wide-ranging study of depletion thus far within the Gould Belt. We estimate CO column densities assuming local thermodynamic equilibrium and, for a selection of sources, using the radiative transfer code RADEX in order to compare the two column density estimation methods. High levels of depletion are seen in the centres of several dust cores in all the clouds. We find that in the gas surrounding protostars, levels of depletion are somewhat lower than for starless cores with the exception of a few highly depleted protostellar cores in Serpens and NGC 2024. There is a tentative correlation between core mass and core depletion, particularly in Taurus and Serpens. Taurus has, on average, the highest levels of depletion. Ophiuchus has low average levels of depletion which could perhaps be related to the anomalous dust grain size distribution observed in this cloud. High levels of depletion are often seen around the edges of regions of optical emission (Orion) or in more evolved or less dynamic regions such as the bowl of L1495 in Taurus and the north-western region of Serpens.

The JCMT Legacy Survey of the Gould Belt: mapping 13CO and C18O in Orion A

The Gould Belt Legacy Survey will map star-forming regions within 500 pc, using HARP (Heterodyne Array Receiver Programme), SCUBA-2 (Submillimetre Common-User Bolometer Array 2) and POL-2 (Polarimeter 2) on the James Clerk Maxwell Telescope (JCMT). This paper describes HARP observations of the J = 3-2 transitions of 13CO and C18O towards Orion A. The 1500-resolution observations cover 5 pc of the Orion filament, including OMC1 (inc. BN-KL and Orion Bar), OMC 2/3 and OMC 4, and allow a comparative study of the molecular gas properties throughout the star-forming cloud. The filament shows a velocity gradient of ~1 km/s /pc between OMC 1, 2 and 3, and high velocity emission is detected in both isotopologues. The Orion Nebula and Bar have the largest masses and line widths, and dominate the mass and energetics of the high velocity material. Compact, spatially resolved emission from CH3CN, 13CH3OH, SO, HCOOCH3, C2H5OH, CH3CHO and CH3OCHO is detected towards the Orion Hot Core. The cloud is warm, with a median excitation temperature of ~24 K; the Orion Bar has the highest excitation temperature gas, at >80 K. The C18O excitation temperature correlates well with the dust temperature (to within 40%). The C18O emission is optically thin, and the 13CO emission is marginally optically thick; despite its high mass, OMC 1 shows the lowest opacities. A virial analysis indicates that Orion A is too massive for thermal or turbulent support, but is consistent with a model of a filamentary cloud that is threaded by helical magnetic fields. The variation of physical conditions across the cloud is reflected in the physical characteristics of the dust cores....continued