Angular Momentum of Dwarf Galaxies

Abstract

We present measurements of baryonic mass Mb and specific angular momentum (sAM) jb in 14 rotating dwarf Irregular (dIrr) galaxies from the LITTLE THINGS sample. These measurements, based on 21cm 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 Mb. The dwarf galaxies show systematically higher jb values than expected from the jb~Mb^{2/3} scaling of spiral galaxies, representative of a scale-free galaxy formation scenario. This offset can be explained by decreasing baryon mass fractions fM=Mb Mdyn (where Mdyn is the dynamical mass) with decreasing Mb (for Mb<10^{11}Msun). We find that the sAM of neutral atomic hydrogen HI alone is about 2.5 times higher than that of the stars. The M-j relation of HI is significantly steeper than that of the stars, as a direct consequence of the systematic variation of the HI fraction with Mb.

6 pages, 3 figures, 1 table

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