  We measure the stellar specific angular momentum jstar=Jstar/Mstar in four
nearby (z~0.1) disk galaxies that have stellar masses Mstar near the break M*
of the galaxy mass function, but look like typical star-forming disks at z~2 in
terms of their low stability (Q~1), clumpiness, high ionized gas dispersion
(40-50 km/s), high molecular gas fraction (20-30%) and rapid star formation
(~20 Msun/yr). Combining high-resolution (Keck-OSIRIS) and large-radius
(Gemini-GMOS) spectroscopic maps, only available at low z, we discover that
these targets have about three times less stellar angular momentum than typical
local spiral galaxies of equal stellar mass and bulge fraction. Theoretical
considerations show that this deficiency in angular momentum is the main cause
of their low stability, while the high gas fraction plays a complementary role.
Interestingly, the low jstar values of our targets are similar to those
expected in the M*-population at higher z from the approximate theoretical
scaling jstar~(1+z)^(-1/2) at fixed Mstar. This suggests that a change in
angular momentum, driven by cosmic expansion, is the main cause for the
remarkable difference between clumpy M*-disks at high z (which likely evolve
into early-type galaxies) and mass-matched local spirals.

Astrophysics of Galaxies