Recent deep photometry of the dwarf spheroidal Ursa Major II ’ s morphology , and spectroscopy of individual stars , have provided a number of new constraints on its properties .
With a velocity dispersion \sim 6 km s ^ { -1 } , and under the assumption that the galaxy is virialised , the mass-to-light ratio is found to be approaching \sim 2000 - apparently heavily dark matter dominated .
Using N-Body simulations , we demonstrate that the observed luminosity , ellipticity , irregular morphology , velocity gradient , and the velocity dispersion can be well reproduced through processes associated with tidal mass loss , and in the absence of dark matter .
These results highlight the considerable uncertainty that exists in measurements of the dark matter content of Ursa Major II .
The dynamics of the inner tidal tails , and tidal stream , causes the observed velocity dispersion of stars to be boosted to values of > 5 km s ^ { -1 } .
These dispersion boosts occur at each apocentre , and last throughout the time the galaxy is close to apocentre .
The model need not be close to destruction to have a boosted velocity dispersion .
We additionally note that the velocity dispersion at apocentre is periodically enhanced substantially ( e.g > 20 km s ^ { -1 } ) .
This occurs most strongly when the model ’ s trajectory is close to perpendicular with the Galaxy ’ s disk at pericentre .
This effect is responsible for raising the velocity dispersion of our model to ( and beyond ) the observed values in UMaII .
We test an iterative rejection technique for removing unbound stars from samples of UMaII stars whose positions on the sky , and line-of-sight velocities , are provided .
We find this technique is very effective at providing an accurate bound mass from this information , and only fails when the galaxy has a bound mass less than 10 \% of its initial mass .
However when < 2 \% mass remains bound , mass overestimation by > 3 orders of magnitude are seen .
Additionally we find that mass measurements are sensitive to measurement uncertainty in line-of-sight velocities .
Measurement uncertainties of 1-4 km s ^ { -1 } result in mass overestimates by a factor of \sim 1.3-5.7 .