While the dark matter content within the most massive giant and smallest dwarf galaxies has been probed – spanning a range of over one million in mass – an important observational gap remains for galaxies of intermediate mass .
This gap covers K band magnitudes of approximately –16 > M _ { K } > –18 mag ( for which dwarf galaxies have B–K \sim 2 ) .
On the high mass side of the gap are dwarf elliptical ( dE ) galaxies , that are dominated by stars in their inner regions .
While the low mass side includes dwarf spheroidal ( dSph ) galaxies that are dark matter-dominated and ultra compact dwarf ( UCD ) objects that are star-dominated .
Evolutionary pathways across the gap have been suggested but remain largely untested because the ‘ gap ’ galaxies are faint , making dynamical measurements very challenging .

With long exposures on the Keck telescope using the ESI instrument we have succeeded in bridging this gap by measuring the dynamical mass for five dwarf galaxies with M _ { K } \sim –17.5 ( M _ { B } \sim –15.5 ) .
With the exception of our brightest dwarf galaxy , they possess relatively flat velocity dispersion profiles of around 20 km s ^ { -1 } .
By examining their 2D scaling relations and 3D fundamental manifold , we found that the sizes and velocity dispersions of these gap galaxies reveal continuous trends from dE to dSph galaxies .
We conclude that low-luminosity dwarf elliptical galaxies are dominated by stars , not by dark matter , within their half light radii .
This finding can be understood if internal feedback processes are operating most efficiently in gap galaxies , gravitationally heating the centrally-located dark matter to larger radii .
Whereas external environmental processes , which can strip away stars , have a greater influence on dSph galaxies resulting in their higher dark matter fractions .
UCDs appear to be more similar to massive compact star clusters than to small galaxies .
Our dynamical study of low mass dwarf elliptical galaxies provides further constraints on the processes that shape some of the smallest and most numerous galaxies in the Universe .