Large‐Scale Structure, Kinematics, and Heating of the Orion Ridge. I. VLA NH3(1, 1) and (2, 2) Multifield Mosaics

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Abstract
We present high-resolution VLA mosaics of 18 adjacent fields in OMC-1 covering an 8' × 4' (1.2 × 0.6 pc) region surrounding the Orion-KL core. The NH3 (J, K) = (1, 1) and (2, 2) inversion transitions were observed; the resulting maps were produced with both high spectral (0.3 km s-1) and high angular (8'') resolution. Both linear and nonlinear (maximum entropy method) techniques were employed to create the mosaics; we compare the challenges and results of each method. The complex effects of chemical excitation are discussed. We find extended clumpy filaments throughout the 0.5 pc region extending to the north and west from Orion-KL. The structure of filaments composed of chains of condensations appears to be hierarchical in OMC-1, as it is found on several scales. The filaments are separated into at least two major velocity components that appear to overlap in the central Orion-KL core region, suggesting interaction between cloud components as a possible triggering mechanism for the active high-mass star formation occurring there. The overlapping nature of the velocity components complicates simple global rotation models for OMC-1. The filaments appear to be fragmented into beadlike chains of dense clumps, which may show a continuing pattern of structural instabilities and star formation in the region. Some of these fragments may be sites, or future sites, of young stars. Some have very large velocity gradients and may be collapsing cores that have not yet shed their angular momentum. We also present a high-resolution NH3 (2, 2) to (1, 1) ratio map of the region, representing the temperature. Striking patterns of heating are apparent: around the central Orion-KL core, strong heating is found in a patchy ring surrounding the Orion bipolar outflow source, possibly delineating the paths by which the outflowing gas exits the central dense region and heats the gas along the way. Heating is evident along the edges of the filaments and clumps that face the path of the outflow, showing direct impact of outflows and radiation on the molecular environment. Other clumps along the filaments show slight temperature enhancements along their outer sheaths, which may be the result of radiation from external stars penetrating the clumpy medium and heating the core sheaths. The complex combination presented here of filaments, fragmentation, kinematical interaction, and heating along the OMC-1 ridge provides evidence for extensive and long-range interaction between a core of high-mass star formation and its surrounding cloud environment.