Candidates of Halpha emitting regions in Magellanic Stream IV cloud

TL;DR

This study reports the discovery of three faint H extalpha emitting filaments in the Magellanic Stream IV, suggesting possible origins from shock heating or local stellar trails, with implications for understanding the stream's ionization sources.

Contribution

First detection of faint H extalpha filaments in MS IV, providing positional data to distinguish between galactic and local origins of the emission.

Findings

Filaments are parallel, 2 arcmin wide, 6-30 arcmin long, with low surface brightness.

Filaments may be part of the Magellanic Stream or local structures like Fossil Stromgren Trails.

Their location supports shock heating models if associated with MS.

Abstract

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 HI map, the position of the filaments overlap MS, suggesting that they are parts of MS, but there also exists a local HI 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 Str\"omgren 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.