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Posts: 131433
Date:
Abell 222/223
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Title: A filament of dark matter between two clusters of galaxies
Authors: Jörg P. Dietrich (1), Norbert Werner (2), Douglas Clowe (3), Alexis Finoguenov (4), Tom Kitching (5), Lance Miller (6), Aurora Simionescu (2) ((1) Physics Dept., University of Michigan, (2) KIPAC, Stanford, (3) Dept. of Physics & Astronomy, Ohio University, (4) MPE, (5) Institute for Astronomy, The University of Edinburgh, (6) Department of Physics, University of Oxford)

It is a firm prediction of the concordance Cold Dark Matter (CDM) cosmological model that galaxy clusters live at the intersection of large-scale structure filaments. The thread-like structure of this "cosmic web" has been traced by galaxy redshift surveys for decades. More recently the Warm-Hot Intergalactic Medium (WHIM) residing in low redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying Dark Matter skeleton, which should contain more than half of all matter, remained elusive, as earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignements of dark and luminous matter. Here we report the detection of a dark matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft X-ray emission and contributes mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. Combined with X-ray observations, we place an upper limit of 0.09 on the hot gas fraction, the mass of X-ray emitting gas divided by the total mass, in the filament.

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Posts: 131433
Date:
Abell 222
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Title: The clusters Abell~222 and Abell~223: a multi-wavelength view
Authors: F. Durret, T. F. Laganá, C. Adami, E. Bertin

The Abell 222 and 223 clusters are located at an average redshift z ~ 0.21 and are separated by 0.26 deg. Signatures of mergers have been previously found in these clusters, both in X-rays and at opticalwavelengths, thus motivating our study. In X-rays, they are relatively bright, and Abell 223 shows a double structure. A filament has also been detected between the clusters both at optical and X-ray wavelengths. We analyse the optical properties of these two clusters based on deep imaging in two bands, derive their galaxy minosity functions (GLFs) and correlate these properties with X-ray characteristics derived from XMM-Newton data. The GLFs of Abell 222 in the g' and r' bands are well fit by a Schechter function; the GLF is steeper in r' than in g'. For Abell 223, the GLFs in both bands require a second component at bright magnitudes, added to a Schechter function; they are similar in both bands. The Serna & Gerbal method allows to separate well the two clusters. No obvious filamentary structures are detected at very large scales around the clusters, but a third cluster at the same redshift, Abell 209, is located at a projected distance of 19.2 Mpc. X-ray temperature and metallicity maps reveal that the temperature and metallicity of the X-ray gas are quite homogeneous in Abell 222, while they are very perturbed in Abell 223. The Abell 222/Abell 223 system is complex. The two clusters that form this structure present very different dynamical states. Signs of recent interactions are also detected in the optical data where this cluster shows a "perturbed" GLF. In summary, the multiwavelength analyses of Abell 222 and Abell 223 are used to investigate the connection between the ICM and the cluster galaxy properties in an interacting system.

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