Evidence for Hα emission associated with the HI bridge connecting the Small and Large Magellanic Clouds

The bridge of matter connecting the Small Magellanic Cloud (SMC) with the Large Magellanic Cloud (LMC) was first detected thanks to radio observations, and detailed maps of this H I bridge are now available¹. Observations of the Magellanic system at Hα wavelength reported by Johnson et al.² in 1982 seem to show a diffuse Hα emission associated with the H I bridge. As they suggested, it is necessary to confirm this association by obtaining Hα profiles in the direction of this bridge. We did this in February 1984 with the help of a scanning Perot-Fabry interferometer and a photon-counting system at the 1.5-m European Space Observatory (ESO) telescope. The choice of the area to be observed was based on recent observations³ with the Very Wide Field Camera (VWFC) on board Spacelab 1 (November 1983) showing an extension of the SMC towards the LMC at wavelengths of 1,930 and 1,650 Å. Detection of Hα emission would check that the ultraviolet emission was emanating from the bridge connecting the two galaxies by showing that the cloud of hot stars giving rise to this ultraviolet emission was ionizing part of the H I bridge.