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

24 pags., 32 figs., 3 tabs.
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-1 is 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 the Herschel/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.
This work is based on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc.(USRA), under NASA contract NAS2-97001, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. This work is carried out within the Collaborative Research Centre 956, subproject [A4], funded by the Deutsche Forschungsgemeinschaft (DFG) – project ID 184018867. We thank the Spanish MICIU for funding support under grant AYA2017-85111-P.