THE SINS/zC-SINF SURVEY OF z similar to 2 GALAXY KINEMATICS: EVIDENCE FOR GRAVITATIONAL QUENCHING

Abstract

As part of the SINS/zC-SINF surveys of high-z galaxy kinematics, we derive the radial distributions of Ha surface brightness, stellar mass surface density, and dynamical mass at similar to 2 kpc resolution in 19 z similar to 2 star-forming disks with deep SINFONI adaptive optics spectroscopy at the ESO Very Large Telescope. 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)-10(11.5) M-circle dot). In more than half of our SFGs, the Ha 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 Ha rings and of large nuclear Q-values appears to be more common for the more massive SFGs. While our sample is small and biased to larger SFGs, and there remain 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.