We report discovery of a dwarf galaxy in the Leo Triplet .
Analysis of the neutral hydrogen distribution shows that it rotates independently of the tidal tail of NGC 3628 , with a radial velocity gradient of 35–40 km s ^ { -1 } over approximately 13 kpc .
The galaxy has a very high neutral gas content , explaining large part of its total dynamic mass – suggesting a small dark matter content .
As it is located at the tip of the gaseous tail , this strongly suggests its tidal origin .
Should it be the case , it would be one of the most confident and closest ( to the Milky Way ) detections of a tidal dwarf galaxy and , at the same time , a most detached from its parent galaxy ( \approx 140 kpc ) object of this type .