The zCOSMOS redshift survey: the role of environment and stellar mass in shaping the rise of the morphology-density relation from z ~ 1

Abstract

Context. For more than two decades we have known that galaxy morphological segregation is present in the Local Universe. It is important to see how this relation evolves with cosmic time. Aims. To investigate how galaxy assembly took place with cosmic time, we explore the evolution of the morphology-density relation up to redshift z ∼ 1 using about 10 000 galaxies drawn from the zCOSMOS Galaxy Redshift Survey. Taking advantage of accurate HST/ACS morphologies from the COSMOS survey, of the well-characterised zCOSMOS 3D environment, and of a large sample of galaxies with spectroscopic redshift, we want to study here the evolution of the morphology-density relation up to z ∼ 1 and its dependence on galaxy luminosity and stellar mass. The multi-wavelength coverage of the field also allows a first study of the galaxy morphological segregation dependence on colour. We further attempt to disentangle between processes that occurred early in the history of the Universe or late in the life of galaxies. Methods. The zCOSMOS field benefits of high-resolution imaging in the F814W filter from the Advanced Camera for Survey (ACS). We use standard morphology classifiers, optimised for being robust against band-shifting and surface brightness dimming, and a new, objective, and automated method to convert morphological parameters into early, spiral, and irregular types. We use about 10 000 galaxies down to I AB = 22.5 with a spectroscopic sampling rate of 33% to characterise the environment of galaxies up to z ∼ 1 from the 100 kpc scales of galaxy groups up to the 100 Mpc scales of the cosmic web. The evolution of the morphology-density relation in different environments is then studied for luminosity and stellar-mass selected, volume-limited samples of galaxies. The trends are described and related to the various physical processes that could play a relevant role in the build-up of the morphology-density relation. Results. We confirm that the morphological segregation is present up to z ∼ 1 for luminosity-selected, volume-limited samples. The behaviour of the morphology-density relation gets flatter at fixed masses expecially above 10 10.6 M . We suggest the existence of a critical mass above which the physical processes governing galaxy stellar mass also determine the shaping of the galaxy more than its environment. We finally show that at a fixed morphology there is still a residual variation in galaxy colours with density. Conclusions. The observed evolution with redshift of the morphology-density relation offers an opportunity to trace the effect of nature and nurture as a function of environment. Even though it is based mainly on a biased view, the environmental dependence of the morphological evolution for luminosity-selected, volume-limited samples seems to indicate that nurture is in play. On the other hand, the lack of evolution observed for earlytype and spiral galaxies that are more massive than 10 10.8 M independents of the environment indicates that nature has imprinted these properties early in the life of...

The impact of galactic properties and environment on the quenching of central and satellite galaxies: a comparison between SDSS, Illustris and L-Galaxies

“…Many prior studies have found evidence for the quenched fraction of satellites exceeding that of centrals at a fixed stellar mass, particularly at lower stellar masses (e.g., Balogh et al 2004;Cortese et al 2006;Moran et al 2007;van den Bosch et al 2007Tasca et al 2009;Peng et al 2012;Hirschmann et al 2013;Wetzel et al 2013;Bluck et al 2014). Taken together, these studies additionally find that the quenching of satellites depends on environmental parameters, such as local (over-)density, halo mass, location within the halo, galaxy clustering, and combinations of these parameters.…”

“…Some credence to this idea comes from the morphology -density relation (e.g., Dressler et al 1980;Bamford et al 2009;Tasca et al 2009;Capellari et al 2011), whereby galaxies are more bulge dominated (and hence have higher central velocity dispersions) for their stellar masses in denser regions of space. The only way to determine to what extent this explanation can account for satellite galaxy quenching is to measure the dependence of satellite quenching on environment at fixed central velocity dispersion.…”

“…Processes such as ram pressure stripping, harassment, strangulation from removal of the satellites' hot gas halo, and pre-processing in groups prior to the cluster environment can all lead to a removal of gas or gas supply and hence a reduction and eventual cessation of star formation (e.g., Balogh et al 2004;Cortese et al 2006;Font et al 2008;Tasca et al 2009;Peng et al 2012;Hirschmann et al 2013;Wetzel et al 2013). Additionally, if a central galaxy enters a group or cluster environment for the first time, transitioning to becoming a satellite, it will no longer reside at a local gravitational minimum in the cosmic web.…”

Where is the Light? Tracing the Evolution of Bulges and Disks since z ~ 0.8

“…Using the zCOSMOS 10k catalogue we have already shown (e.g., Tasca et al 2009;Bolzonella et al 2010;Pozzetti et al 2010;Peng et al 2010, among others) that stellar mass is the main driver of the observed dependencies of galaxy properties on the environment. Still the environment playing an important, although secondary, role.…”

“…The final sample of 20, 707 objects, the so-called "20k bright", has been assembled providing the needed statistics. In addition, the high spectroscopic sampling rate (∼ 70%) and the complete coverage of the COSMOS field with the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) (Koekemoer et al 2007), allows to perform on one side an accurate reconstruction of the density field (Kovač et al 2010) and on the other a robust morphological classification (Tasca et al 2009) and bulge/disk decomposition.…”