  As part of the SINS/zC-SINF surveys of high-z galaxy kinematics, we derive
the radial distributions of H-alpha surface brightness, stellar mass surface
density, and dynamical mass at ~2 kpc resolution in 19 z~2 star-forming disks
with deep SINFONI AO spectroscopy at the ESO VLT. From these data we infer the
radial distribution of the Toomre Q-parameter for these main-sequence star
forming galaxies (SFGs), covering almost two decades of stellar mass (10^9.6 to
10^11.5 solar masses). In more than half of our SFGs, the H-alpha distributions
cannot be fit by a centrally peaked distribution, such as an exponential, but
are better described by a ring, or the combination of a ring and an
exponential. At the same time the kinematic data indicate the presence of a
mass distribution more centrally concentrated than a single exponential
distribution for 5 of the 19 galaxies. The resulting Q-distributions are
centrally peaked for all, and significantly exceed unity there for three
quarters of the SFGs. The occurrence of H-alpha rings and of large nuclear
Q-values is strongly correlated, and is more common for the more massive SFGs.
While our sample is small and there remain substantial uncertainties and
caveats, our observations are consistent with a scenario in which cloud
fragmentation and global star formation are secularly suppressed in gas rich
high-z disks from the inside out, as the central stellar mass density of the
disks grows.
