ANGULAR MOMENTUM OF DWARF GALAXIES

We present measurements of baryonic mass M-b and specific angular momentum (sAM) j(b) in 14 rotating dwarf Irregular (dIrr) galaxies from the LITTLE THINGS sample. These measurements, based on 21 cm kinematic data from the Very Large Array and stellar mass maps from the Spitzer Space Telescope, extend previous AM measurements by more than two orders of magnitude in M-b. The dwarf galaxies show systematically higher j(b) values than expected from the j(b) proportional to M-b(2/3) scaling of spiral galaxies, representative of a scale-free galaxy formation scenario. This offset can be explained by decreasing baryon mass fractions f(M) = M-b/M-dyn (where M-dyn is the dynamical mass) with decreasing M-b (for M-b < 10(11) M-circle dot 11). We find that the sAM of neutral atomic hydrogen (H I) alone is about 2.5 times higher than that of the stars. The M-j relation of H I is significantly steeper than that of the stars, as a direct consequence of the systematic variation of the H I fraction with M-b.