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The WINGS Survey


The WIde-field Nearby Galaxy-cluster Survey (WINGS) is a project aiming at the study of the galaxy populations in clusters in the local universe (0.04<z<0.07) and the influence of environment on the physical properties of galaxies. This survey provides a high quality set of spectroscopic data for ~6000 galaxies in 48 clusters.

Galaxies of different morphology are not evenly distributed. It is now more than 70 years since Hubble & Humason first noticed that (in the local universe) spiral galaxies are abundant in the field while S0 and elliptical galaxies dominate in denser regions. Gravitational interaction apparently affects the global properties of the galaxies even in low density environments, and even such field galaxies show significant differences with respect to truly isolated systems that have been free of interaction for a long period of time.

Clusters of galaxies are dense peaks in the galaxy distribution and therefore appropriate sites to look for changes in the properties of the galaxies. They can be therefore used to trace the evolution of the systems themselves as well as that of the galaxies in them. Such a systematic analysis certainly needs a fair knowledge of the properties of local clusters of galaxies and their content (the end point of the evolution), extensive enough to cope not only with the average properties but also with their physical variance. This is unfortunately still lacking. As a matter of fact, while a large amount of high quality data for distant clusters is continuously being gathered from both the Hubble Space Telescope (HST) observations and large ground-based telescopes, our present knowledge of the systematic properties of galaxies in nearby clusters, remains surprisingly limited, with Virgo, Coma and Fornax as the main references.

The principal goal of the WINGS project is to elaborate a statistically meaningful, high quality database of the properties of nearby clusters of galaxies and of the galaxies that populate them. Hopefully, this will serve to improve the knowledge of clusters and cluster galaxies in the local universe and will provide the reference to gauge the changes with redshift over their physical variance at a given z.

In broad terms, the goals of the project are to characterize the global properties of clusters taken as systems, and those of their member galaxies. Among the former, besides the already existing data on the X-ray luminosity, they include their total luminosity and size, the velocity dispersion, the presence of substructures and the cluster scaling relations. This will allow astreonomers to explore the existence of well defined relations among structural parameters and characterize the actual range of those properties.

Regarding the member galaxies, the primary goals are to analyze the variance of the morphological fractions (E/S0/S/Irr), their distribution in the clusters and the morphology-density relation. The analysis of the colors and the spectral information will provide the data necessary to retrace the star formation history of galaxies in nearby clusters.

The WINGS-SPE survey consists of multifiber spectroscopy of galaxies in 51 clusters from the master WINGS sample, obtained with the AF2 on the WHT and 2dF on the AAT.The NIR photometric survey obtained data for ~50 clusters (WINGS-NIR) and WINGS-HAL and WINGS-UV has imaged ~1 square degree of 10 WINGS clusters in H-alpha and U-band respectively using the WFC on the INT.

Mosaic of the WFC@INT image of the cluster A151. North is up, East is left. The field of view is 34'×34'. (Extracted from G. Fasano et al., 2008, A&A, 445, 805) [ GIF ].

According to the current cosmological paradigm, large structures in the Universe form hierarchically. Clusters of galaxies are the largest structures that have grown through mergers of smaller units and have achieved near dynamical equilibrium. In the hierarchical scenario, clusters are a rather young population, and we should be able to observe their formation process even at rather low redshifts. A signature of such process is the presence of cluster substructures. A cluster is said to contain substructures (or subclusters) when its surface density is characterized by multiple, statistically significant peaks on scales larger than the typical galaxy size, with "surface density'' being referred to the cluster galaxies, the intra-cluster (IC) gas or the dark matter. Studying cluster substructure therefore allows astronomers to investigate the process by which clusters form, constrain the cosmological model of structure formation, and ultimately test the hierarchical paradigm itself. In addition, it also allows us to better understand the mechanisms affecting galaxy evolution in clusters, which can be accelerated by the perturbative effects of a cluster-subcluster collision and of the tidal field experienced by a group accreting onto a cluster.

The WINGS survey team were able to identify at least one reliable structure in the field of 55 clusters. 40 of these clusters have a total of 69 substructures at the same redshift of the cluster (redshift estimates of substructures are from color-magnitude diagrams). The fraction of clusters with subclusters (73%) is higher than in most studies. The presence of subclusters affects the relative luminosities of the brightest cluster galaxies. They also applied a spectrophotometric model to cluster galaxies to study their stellar content, and analysed the fundamental plane of early type-type galaxies in 59 clusters.

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Last modified: 13 December 2010