Morphological fractions of galaxies in WINGS clusters: revisiting the morphology–density paradigm

Abstract

We present the Morphology-Density and Morphology-Radius relations (T -Σ and T -R, respectively) obtained from the WINGS database of galaxies in nearby clusters. Aiming to achieve the best statistics, we exploit the whole sample of galaxies brighter than M V = −19.5 (5,504 objects), stacking up the 76 clusters of the WINGS survey altogether.Using this global cluster sample, we find that the T -Σ relation holds only in the inner cluster regions (R < 1/3 × R 200 ), while the T -R relation keeps almost unchanged over the whole range of local density. A couple of tests and two sets of numerical simulations support the robustness of these results against the effects of the limited cluster area coverage of the WINGS imaging. The above mentioned results hold for all cluster masses (X-ray luminosity and velocity dispersion) and all galaxy stellar masses (M * ). The strength of the T -Σ relation (where present) increases with increasing M * , while this effect is not found for the T -R relation.Noticeably, the absence/presence of subclustering determines the presence/absence of the T -Σ relation outside the inner cluster regions, leading us to the general conclusion that the link between morphology and local density is preserved just in dynamically evolved regions. We hypothesize that some mechanism of morphological broadening/redistribution operates in the intermediate/outer regions of substructured ("non relaxed") clusters, producing a strong weakening of the T -Σ relation.

Structural and dynamical modeling of WINGS clusters

“…We find that in general the NFW profile is preferred over the cored-King profile, but this is less and less evident for late-type galaxies and Irr clusters. The spatial distributions become increasingly more concentrated towards earlier morphological classes, and this reflects the well-known morphologyradius relation (Sanromà & Salvador-Solé 1990;Whitmore et al 1993;Fasano et al 2015, and references therein). The velocity distributions were described in terms of the velocity dispersion profiles, that we modeled with the analytical profile of Eq.…”

“…-The concentration, r 200 /r s or r 200 /r c , increases from E to S0 to S galaxies, both in Reg and Irr clusters, reflecting the well-known morphology-radius relation (Sanromà & Salvador-Solé 1990;Whitmore et al 1993;Fasano et al 2015). -The concentration is higher in Reg than in Irr clusters for both E and S0 galaxies, but not for spirals.…”

“…They considered 5504 spectroscopically confirmed members of 76 nearby clusters, down to an absolute magnitude limit M V = −19.5. Fasano et al (2015) found that the morphology-radius relation remains valid at all densities, while the morphologydensity relation is valid only in the inner cluster regions, and outside the inner regions only for very regular clusters without substructures. This result does not depend on the cluster mass, nor on the galaxy stellar mass.…”

“…In this paper we extend the work of Fasano et al (2015) by analyzing not only the spatial, but also the velocity distributions of WINGS cluster member galaxies of three morphological classes, E, S0, and S. Based on the results of Fasano et al (2015), we use the clustercentric distance, rather than the local density, to parametrize the spatial distribution of different galaxy types. The morphological segregation in clustercentric distance is analyzed by comparison of the number density profiles (NDPs) of the three morphological classes.…”

“…The cluster velocity dispersion is mildly dependent on the morphological fraction (Desai et al 2007), not only in low-z but also in high-z clusters, up to z ≈ 1 at least. Fasano et al (2015) have recently revisited the morphologydensity paradigm, using the WIde-field Nearby Galaxy-cluster Survey (WINGS) database of galaxies in nearby clusters. They considered 5504 spectroscopically confirmed members of 76 nearby clusters, down to an absolute magnitude limit M V = −19.5.…”