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[OI] contribution to dense gas in NGC 7023 PDR

Published onJun 01, 2020
[OI] contribution to dense gas in NGC 7023 PDR

NGC 7023 is a photodissociation region (PDR) which has been studied extensively with ground-based telescopes, Herschel, and SOFIA/GREAT. In previous observations on [CII] line shows a double peak feature. This feature could be due to self-absorption or an additional velocity component. To determine the reason behind the double peak feature, we observed [OI] 63 μm line with SOFIA/GREAT across the North-West PDR in NGC 7023. This is the same area as was previously observed in Herschel/HIFI on [CII] and the area crosses the densest material in the PDR (Ossenkopf et al. 2013). The map covers a range of densities, column densities, and distances from the illuminating star so that it allows to distinguish the impact of the different parameters. Berné et al. (2012) found several components in [CII] emission and they suggested that the high-velocity component arises in diffuse gas. However, this component is what we see in [OI], which would suggest that the high-velocity component is actually more dense. We can speculate on the nature of this gas based on the comparison of our data to previous observations of [CII] and [OI] (Herschel/PACS).

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