Abstract
Abstract We mapped the kinetic temperature structure of Orion KL in a ∼20″ (∼8000 au) sized region with para-H2CS 707 − 606, 726 − 625, and 725 − 624 making use of Atacama Large Millimeter/submillimeter Array Band 6 Science Verification data. The kinetic temperatures obtained with a resolution of 1.″65 × 1.″14 (∼550 au) are deduced by modeling the measured averaged velocity-integrated intensity ratios of para-H2CS 726 − 625/707 − 606 and 725 − 624/707 − 606 with a RADEX non-LTE model. The kinetic temperatures of the dense gas, derived from the para-H2CS line ratios at a spatial density of 107 cm−3, are high, ranging from 43 to >500 K with an unweighted average of ∼170 K. There is no evidence for internal sources playing an important role in the heating of the various structures identified in previous work, namely the elongated ridge, the northwestern clump, and the eastern region of the compact ridge, while the high temperatures in the western region of the compact ridge may be dominated by internal massive star formation. Significant gradients of kinetic temperature along molecular filaments traced by H2CS indicate that the dense gas is heated by the shocks induced by the enigmatic explosive event which occurred several hundred years ago and greatly affected the energetics of the Orion KL region. Thus, with the notable exception of the western region of the compact ridge, the high temperatures of the dense gas in Orion KL are probably caused by shocks from the explosive event, leading to a dominant component of externally heated dense gas.
Highlights
Significant gradients of kinetic temperature along molecular filaments traced by H2CS indicate that the dense gas is heated by the shocks induced by the enigmatic explosive event, which occurred several hundred years ago greatly affecting the energetics of the Orion KL region
No compact source is detected in the northwestern clump where the continuum emission detected in our data is completely resolved in higher angular resolution Atacama Large Millimeter/submillimeter Array (ALMA) data (Hirota et al 2015)
The kinetic temperatures are derived from the measured averaged velocity-integrated intensity ratios of para-H2CS 726 − 625/707 − 606 and 725 − 624/707 − 606 with RADEX non-LTE modeling, which provides a monotonic increase in line ratios with rising kinetic temperatures
Summary
Emission in the CO J = 2–1 line was recently imaged with the Atacama Large Millimeter/submillimeter Array (ALMA) It shows at velocities outside of vLSR = 0 to 20 km s−1 a large number of radial streamers covering the entire range of position angles and occupying a region with radius 50 (Bally et al 2017). Based on their Very Large Array (VLA) proper motion determinations, Rodrıguez et al (2017) determine the year 1445 ± 6 as the time when the most prominent radio sources, Source I (in the following Src I) and the Becklin-Neugebauser object (BN), were closest together
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