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 \sim 2 Gyr between the average redshifts z \sim 2.2 and z \sim 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 \sim 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 ( log L _ { X } < 44.5 erg s ^ { -1 } ) played a key role at z \gtrsim 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 < log ( { \cal M } / M _ { \odot } ) < 11 .