Neutral hydrogen observations of spiral and irregular galaxies

Abstract

This thesis describes hydrogen-line observations using the Cambridge Half-Mile telescope. The initial chapters describe observations of two nearby galaxies af late spiral type, namely M33 and NGC 2403. The severe warping of the HI layer in the outer parts of M33 was clearly seen, and the origin of this phenomenon is discussed. Sensitive low-resolution maps reveal only a very slight warp in NGC 2403, while maps at the full resolution allowed the dynamical parameters to be investigated and showed several features associated with spiral structure. The later chapters describe observations of irregular galaxies, many belonging to the class IrII which was of particular interest. NGC 1569, a dwarf irregular galaxy, has been the subject of interest due to its prominent Ha [Greek letter alpha] filaments. Observations reveal that the overall HI distribution to be that expected of a disc in normal rotation, although there are several unusual features. Arp 205 consists of an IrII galaxy (NGC 3448) and a dwarf companion less than one diameter away. A model for the HI dynamics is presented which suggests that there has been a planar tidal interaction between these two galaxies. NGG 2805, NGC 2814, NGG 2820 and 10 2458 form a compact group of galaxies of which NGC 2805 is the brightest. HI was detected in all except NGC 2814, and there is good evidence for a HI bridge linking NGC 2820 and IC 2458. It is postulated that the HI bridge and disturbed nature of this group are the result of a gravitational interaction. Less detailed observations of other irregular galaxies are also presented in this thesis, including NGC 3432 and NGG 3310.