Abstract
We measure the stellar specific angular momentum jstar=Jstar/Mstar in four
nearby (redshift 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 \~3 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.
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