zCOSMOS 20k: satellite galaxies are the main drivers of environmental effects in the galaxy population at least to z ∼ 0.7
Kneib, J. -P.; Aussel, H.; Le Floc'h, E.; Bolzonella, M.; Tanaka, M.; Silverman, J.; Mainieri, V.; Koekemoer, A. M.; Caputi, K.; Carollo, C. M.; Mignoli, M.; Zamorani, G.; Tasca, L.; Peng, Y.; Garilli, B.; Moresco, M.; Pozzetti, L.; Bardelli, S.; Zucca, E.; Cucciati, O.; Oesch, P.; Scodeggio, M.; Bongiorno, A.; Lilly, S. J.; Renzini, A.; Pello, R.; Contini, T.; Tresse, L.; Kampczyk, P.; de la Torre, S.; de Ravel, L.; Franzetti, P.; Iovino, A.; Knobel, C.; Kovač, K.; Lamareille, F.; Le Borgne, J. -F.; Le Brun, V.; Maier, C.; Vergani, D.; Le Févre, O.; Presotto, V.; Bschorr, T. J.; Montero, E. Perez
Switzerland, France, Germany, Italy, Netherlands, United Kingdom, Austria, United States, Spain, Japan
Abstract
We explore the role of environment in the evolution of galaxies over 0.1 < z < 0.7 using the final zCOSMOS-bright data set. Using the red fraction of galaxies as a proxy for the quenched population, we find that the fraction of red galaxies increases with the environmental overdensity δ and with the stellar mass M*, consistent with previous works. As at lower redshift, the red fraction appears to be separable in mass and environment, suggesting the action of two processes: mass ɛm(M*) and environmental ɛρ(δ) quenching. The parameters describing these appear to be essentially the same at z ∼ 0.7 as locally. We explore the relation between red fraction, mass and environment also for the central and satellite galaxies separately, paying close attention to the effects of impurities in the central-satellite classification and using carefully constructed samples well matched in stellar mass. There is little evidence for a dependence of the red fraction of centrals on overdensity. Satellites are consistently redder at all overdensities, and the satellite quenching efficiency, ɛsat(δ, M*), increases with overdensity at 0.1 < z < 0.4. This is less marked at higher redshift, but both are nevertheless consistent with the equivalent local measurements. At a given stellar mass, the fraction of galaxies that are satellites, fsat(δ, M*), also increases with overdensity. The obtained ɛρ(δ)/fsat(δ, M*) agrees well with ɛsat(δ, M*), demonstrating that the environmental quenching in the overall population is consistent with being entirely produced by a satellite quenching process at least up to z = 0.7. However, despite the unprecedented size of our high-redshift samples, the associated statistical uncertainties are still significant and our statements should be understood as approximations to physical reality, rather than physically exact formulae.