The Magellanic Stream

While not a galaxy, the Magellanic Stream is thought to be related to the Magellanic Clouds, forming a long ribbon of high-velocity clouds of hydrogen gas extending from the LMC and the SMC over a 100° arc...

...with velocities increasingly negative from the right (near the MCs) of the green curve, to the left, as this graph of velocity versus angle along the curve shows...

The Magellanic Stream - although not a galaxy as such - makes an interesting HI line extra-galactic target.