  We report the detection of ubiquitous powerful nuclear outflows in massive (>
10^11 Msun) z~2 star-forming galaxies (SFGs), which are plausibly driven by an
Active Galactic Nucleus (AGN). The sample consists of the eight most massive
SFGs from our SINS/zC-SINF survey of galaxy kinematics with the imaging
spectrometer SINFONI, six of which have sensitive high-resolution adaptive
optics (AO) assisted observations. All of the objects are disks hosting a
significant stellar bulge. The spectra in their central regions exhibit a broad
component in Halpha and forbidden [NII] and [SII] line emission, with typical
velocity FWHM ~ 1500 km/s, [NII]/Halpha ratio ~ 0.6, and intrinsic extent of 2
- 3 kpc. These properties are consistent with warm ionized gas outflows
associated with Type 2 AGN, the presence of which is confirmed via independent
diagnostics in half the galaxies. The data imply a median ionized gas mass
outflow rate of ~ 60 Msun/yr and mass loading of ~ 3. At larger radii, a weaker
broad component is detected but with lower FWHM ~ 485 km/s and [NII]/Halpha ~
0.35, characteristic for star formation-driven outflows as found in the
lower-mass SINS/zC-SINF galaxies. The high inferred mass outflow rates and
frequent occurrence suggest the nuclear outflows efficiently expel gas out of
the centers of the galaxies with high duty cycles, and may thus contribute to
the process of star formation quenching in massive galaxies. Larger samples at
high masses will be crucial to confirm the importance and energetics of the
nuclear outflow phenomenon, and its connection to AGN activity and bulge
growth.
