  We consider the hypothesis that galactic dark matter is composed of
ultra-light scalar particles and use internal properties of dwarf spheroidal
galaxies to establish a preferred range for the mass m of these bosonic
particles. We re-investigate the problem of the longevity of the cold clump in
Ursa Minor and the problem of the rapid orbital decay of the globular clusters
in Fornax and dwarf ellipticals. Treating the scalar field halo as a rigid
background gravitational potential and using N-body simulations, we have
explored how the dissolution timescale of the cold clump in Ursa Minor depends
on m. It is demonstrated that for masses in the range 0.3x10^-22 eV < m
<1x10^-22 eV, scalar field dark halos without self-interaction would have cores
large enough to explain the longevity of the cold clump in Ursa Minor and the
wide distribution of globular clusters in Fornax, but small enough to make the
mass of the dark halos compatible with dynamical limits. It is encouraging to
see that this interval of m is consistent with that needed to suppress the
overproduction of substructure in galactic halos and is compatible with the
acoustic peaks of cosmic microwave radiation. On the other hand, for
self-interacting scalar fields with coupling constant l, values of m^4/l <=
0.55x10^3 eV^4 are required to account for the properties of the dark halos of
these dwarf spheroidal galaxies.
