The HI Content of the W80 Dark Cloud on Scales from 20 to 0.3 pc

Extract

The dark cloud between the North America and Pelican Nebula has been mapped in HI using DRAO synthesis telescope at Penticton, B.C.(Canada) and the 100m telescope at Effelsberg (MPIfR Bonn, F.R.G.) for the short baselines. The angular resolution is 2'= 0.3 pc, assuming 500 pc for the dark cloud distance (Strayzis et al. 1989, Wendker et al. 1983). The spectral resolution was 1.3 km/s. The main part of the dark cloud has been mapped also in the CO (J=1−0) line with the 3m telescope on the Gornergrat (KOSMA, Switzerland) with resolutions of 3.8' and 0.6 km/s. The distribution of HI emission is far from homogenous. The line maps are dominated by irregular patches of up to 10 pc size and systems of filaments up to 20 pc size with substructure down to 1 pc. At radial velocities associated with that of the dark cloud, the HI emission tends to outline the shape of the bulk of the molecular gas seen in the CO data. It could be regarded as the outmost layers of the dark cloud, in which the molecular hydrogen is dissociated by the interstellar radiation field and especially by the ionizing star(s) of the nearby HII region.