CANDIDATES OF Hα EMITTING REGIONS IN THE MAGELLANIC STREAM IV CLOUD

From Hα narrowband observations, we identified three Hα emitting regions in the direction of Magellanic Stream IV (MS IV). They consist of three parallel filaments of 2 arcmin width and 6-30 arcmin length at 12 arcmin intervals. Their mean surface brightness (SB) is ∼2 × 10–18 erg s–1 cm–2 arcsec–2. Because of their low SB, the regions were not detected in previous Hα surveys. In the H I map, the position of the filaments overlap MS, suggesting that they are parts of the MS, but there also exists a local H I structure. If the filaments are associated with the MS, the sizes are 30 pc × 100-500 pc. The filaments lie at the leading edge of a downstream cloud, which supports shock heating and its propagation (shock cascade) model for the ionizing source. If they are local objects, on the other hand, Fossil Strömgren Trails of more than two stars is a possible interpretation, and the sizes would be 0.1 pc × 0.3-1.5 pc at 180 pc distance. The positional information of the Hα filaments presented in this Letter enables future spectroscopic observations to clarify their nature.