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 _ { \phi } 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 _ { \phi } .
It is demonstrated that for masses in the range 0.3 \times 10 ^ { -22 } eV < m _ { \phi } < 1 \times 10 ^ { -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 _ { \phi } 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 \lambda , values of m _ { \phi } ^ { 4 } / \lambda \lesssim 0.55 \times 10 ^ { 3 } eV ^ { 4 } are required to account for the properties of the dark halos of these dwarf spheroidal galaxies .