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Herschel Cluster Surveys (Virgo, Fornax, Coma)

Nearby Galaxy Clusters as seen by Herschel

Clusters of galaxies are unique laboratories for investigating the dependence of galaxy evolution on their environment. Galaxies in clusters are subject to processes that are not present in other environments i.e. ram pressure stripping and tidal interactions. Clusters in themselves vary as to their properties i.e. galaxy numbers and densities. The Virgo cluster of galaxies is a relatively populous system, consisting of about 1500 cataloged members. It is the nearest galaxy cluster to our own Galaxy at a distance of about 17 Mpc. Fornax is just a few Mpc further away than Virgo and is much poorer having a few hundred catalogued galaxies. Coma is a massive cluster consisting of 1000s of galaxies that lies about six times further away than Virgo. The proximity of these clusters means that they can be studied by Herschel and other surveys at a level of detail that will never be possible with more distant systems.

Studies of nearby clusters, particularly Virgo, at different wavelengths (e.g. X-ray, ultraviolet, optical near-infrared, radio) have largely shaped our knowledge of the effects of the cluster environment on the different galactic components (e.g. stars and gas) and on galaxy evolutionary history in general. However, the cold dust (< 30 K) properties of cluster galaxies and the ICM are almost completely unknown. The emission from dust this cold falls within Far Infrared (FIR) to sub-millimeter range of the electromagnetic spectrum. Understanding of the role played by the cluster environment on the dust cycle in a galaxy is not only important for understanding galaxy evolution but also to gain additional insight into the accretion and enrichment history of clusters of galaxies.

The launch of Herschel opened up a new era for submillimeter astronomy, allowing the first accurate measurements of the dust emission in galaxies of all morphological types and luminosities. The HeVICS project (Virgo) was awarded 293 hours of Open Key Project Time to map the cluster. The HeFoCS project was awarded 34 hours of Open Time to map the Fornax cluster. The COMA cluster data was observed as part of H-ATLAS. Each cluster was observed at 100, 160, 250 350 and 500µm. The data will be used to study the dust properties in these nearby galaxies and the role played by dust in the star-formation cycle. Eventually the data will be combined with new data at UV, optical and near infrared to study the star formation histories of cluster galaxies. These surveys will provide the local cluster benchmark for environmental studies and comparison with younger distant clusters and field galaxies.

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