Properties and environment of radio-emitting galaxies in the VLA-zCOSMOS survey

摘要

Aims. We investigate the properties and the environment ofradio sources with optical counterparts from the combined VLA-COSMOSand zCOSMOSsamples. The advantage of this sample is theavailability of optical spectroscopic informations, high qualityredshifts, and accurate density determination. Methods. By comparing the star formation rates estimated fromthe optical spectral energy distribution with those based on the radioluminosity, we divide the radio sources in to three families passiveAGN, non-passive AGN, and star-forming galaxies. These families occupyspecific regions of the 8.0-4.5m infrared color- specific star-formation plane, from which we extract the corresponding control samples. Results. Only the passive AGN have a significantly differentenvironmental distribution from their control sample. The fraction ofradio-loud passive AGN increases from in underdense regions to for overdensities ()greaterthan10. This trend is also present as a function of richness ofthe groups hosting the radio sources. Passive AGN in overdensities tendto have higher radio luminosities than those in lower densityenvironments. Since the black hole mass distribution is similar in bothenvironments, we speculate that, for low radio luminosities, the radioemission is controlled (byfuel availability or confinement of theradio jet by local gas pressure) by the interstellar medium of the hostgalaxy, while in other cases it is determined by the structure (groupor cluster) in which the galaxy resides. Key words: galaxies: fundamental parameters - galaxies: general- galaxies: luminosity function, mass function - radio continuum:galaxies - radio continuum: planetary systems