H i aperture synthesis of the southern barred spiral NGC 1313

Abstract

Aperture synthesis maps have been made of the late-type barred spiral NGC 1313 in the continuum at 1.4 GHz and in the atomic hydrogen line with resolutions of 1 kpc and 16 km s"1. Analysis of the hydrogen distribution and the velocity field indicates that, in addition to the normal emission from a galaxy of this type, there is a tidal interaction in progress between NGC 1313 and a nearby disrupted satellite galaxy. The interaction has resulted in a loop of hydrogen that may have been pulled out of the plane of NGC 1313. The rest of the velocity field can be interpreted in terms of pure circular rotation, and a rotation curve is derived. At the limit of the rotation data, the dark halo contributes about 85 per cent of the enclosed mass. Half of the continuum emission corresponds to the bar and spiral arms of the galaxy, while the rest is due to a compact object with an unusual (positive) spectral index. A recent analysis of archival optical and X-ray data has led Ryder ct al. to identify this compact object as a very unusual Type II supernova (SN 1978K).