  The relationships between galaxies of intermediate stellar mass and moderate
luminosity active galactic nuclei (AGNs) at 1<z<3 are investigated with the
Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample
complemented with public data in the GOODS-South field. Using X-ray data,
hidden AGNs are identified in unsuspected star-forming galaxies with no
apparent signs of non-stellar activity. In the color-mass plane, two parallel
trends emerge during the ~2 Gyr between the average redshifts z~2.2 and z~1.3:
while the red sequence becomes significantly more populated by ellipticals, the
majority of AGNs with L(2-10 keV)>10^42.3 erg s^-1 disappear from the blue
cloud/green valley where they were hosted predominantly by star-forming systems
with disk and irregular morphologies. These results are even clearer when the
rest-frame colors are corrected for dust reddening. At z~2.2, the ultraviolet
spectra of active galaxies (including two Type 1 AGNs) show possible gas
outflows with velocities up to about -500 km s^-1 that are not observed neither
in inactive systems at the same redshift, nor at lower redshifts. Such outflows
indicate the presence of gas that can move faster than the escape velocities of
active galaxies. These results suggest that feedback from moderately luminous
AGNs (logL_X<44.5 erg s^-1) played a key role at z>~2 by contributing to
outflows capable of ejecting part of the interstellar medium and leading to a
rapid decrease in the star formation in host galaxies with stellar masses
10<logM<11 M_Sun.
