From H \alpha narrow band observations , we identified three H \alpha emitting regions in the direction of Magellanic Stream IV ( MS IV ) .
They consist of three parallel filaments with 2 arcmin width and 6 – 30 arcmin length at 12 arcmin intervals .
The mean surface brightness of them is \sim 2 \times 10 ^ { -18 } erg s ^ { -1 } cm ^ { -2 } arcsec ^ { -2 } .
Because of their low surface brightness , the regions were not detected in previous H \alpha surveys .
In H i map , the position of the filaments overlap MS , suggesting that they are parts of MS , but there also exists a local H i structure .
If the filaments associate with MS , the sizes are 30 pc \times 100 – 500 pc .
The filaments lie at the leading edge of a downstream cloud , which supports a 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 \times 0.3 – 1.5 pc at 180 pc distance .
The positional information of the H \alpha filaments presented in this letter enables us future spectroscopic observations to clarify their nature .