HI Surveys of the Magellanic System

Abstract

The global distribution of HI in the Magellanic System is shown in Figure 1. The gas covers some 1500 square degrees of sky and has a mass of 1.8 × 109 M⊙. There are four main components: the LMC, the SMC, the inter-Cloud region and the Magellanic Stream. The integrated HI of the first three components is mapped in Figure 2 with the Parkes 64-m radio telescope which has a resolution of 15 arc min. The previous surveys of McGee and Milton (1966), Hindman (1967), Mathewson et al. (1979) have been combined with a recent survey by Mathewson et al. (1983) of the outer regions of the System to give this large-scale picture of the gas distribution. The last two surveys were made with a velocity resolution of 4.12 km s−1 and a minimum detectable signal of 0.2 K. The long spurs extending from the LMC and SMC and the bridge joining the two galaxies with prominent spurs pointing to the Magellanic Stream are all compelling evidence for tidal interaction between the LMC and SMC (Mathewson 1976a, Murai and Fujimoto 1980). The detailed velocity field of the HI is given in Mathewson et al. (1983). Its large-scale features are shown in Figure 5 of Mathewson et al. (1979) which indicate that the radial velocities of the inter-Cloud region form a velocity continuum with those of the LMC and SMC. This plus the continuity of the general velocity gradient across the entire Magellanic System strongly suggest that the two galaxies are bound.