  The rotational properties of the visible and dark components of low-mass disk
galaxies (vrot<=100 km/s) are investigated using the Swaters sample. The
rotational parameter lambda'=lambda_DM*(j_d/m_d) is determined, where lambda_DM
is the dark halo spin parameter and j_d/m_d is the ratio between the specific
angular momentum of the disk and that of the dark halo. The distribution of
lambda' is in excellent agreement with cosmological predictions of hierarchical
clustering if j_d/m_d=1, that is if the protogalactic gas did not loose a
significant amount of specific angular momentum due to dynamical friction. This
result is in disagreement with current cosmological Nbody/SPH simulations where
the baryonic component looses 90% of its specific angular momentum while
settling into the equatorial plane. The Swaters sample also shows a
surprisingly strong correlation between lambda' and the baryonic mass fraction
m_d: lambda'=0.4 m_d**0.6. This correlation can be explained if the total
amount of gas in protogalaxies is a universal fraction of their dark matter
mass, of order 10%, and if the variation in m_d is a result of the fact that
only the inner parts of the primordial gas distribution managed to form a
visible disk component. In this case the specific angular momentum of the gas
out of which the disk formed is a factor of 2.75 larger than that of the dark
halo, which would require a yet unknown spin-up process for the visible
baryonic component.
