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Title:
Detection of hot gas in the filament connecting the clusters of galaxies Abell 222 and Abell 223
Authors:
Werner, N.; Finoguenov, A.; Kaastra, J. S.; Simionescu, A.; Dietrich, J. P.; Vink, J.; Böhringer, H.
Affiliation:
AA(SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands ), AB(Max-Planck-Institut für Extraterrestrische Physik, 85748 Garching, Germany), AC(SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands; Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands), AD(Max-Planck-Institut für Extraterrestrische Physik, 85748 Garching, Germany), AE(ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany), AF(Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands), AG(Max-Planck-Institut für Extraterrestrische Physik, 85748 Garching, Germany)
Publication:
Astronomy and Astrophysics, Volume 482, Issue 3, 2008, pp.L29-L33 (A&A Homepage)
Publication Date:
05/2008
Origin:
EDP
Keywords:
cosmology: large-scale structure of Universe, X-rays: galaxies: clusters, galaxies: clusters: individual: Abell 222, galaxies: clusters: individual: Abell 223
DOI:
10.1051/0004-6361:200809599
Bibliographic Code:
2008A&A...482L..29W

Abstract

Context: About half of the baryons in the local Universe are invisible and - according to simulations - their dominant fraction resides in filaments connecting clusters of galaxies in the form of low density gas with temperatures in the range of 105 < T < 107 K. This warm-hot intergalactic medium has never been detected indisputably using X-ray observations. Aims: We aim to probe the low gas densities expected in the large-scale structure filaments by observing a filament connecting the massive clusters of galaxies A 222 and A 223 (z = 0.21), which has a favorable orientation approximately along our line-of-sight. This filament has been previously detected using weak lensing data and as an over-density of colour-selected galaxies. Methods: We analyse X-ray images and spectra obtained from a deep observation (144 ks) of A 222/223 with XMM-Newton. Results: We present observational evidence of X-ray emission from the filament connecting the two clusters. We detect the filament in the wavelet-decomposed soft-band (0.5-2.0 keV) X-ray image with a 5σ significance. Following the emission down to the 3σ significance level, the observed filament is ≈1.2 Mpc wide. The temperature of the gas associated with the filament, determined from the spectra, is kT = 0.91±0.25 keV, and its emission measure corresponds to a baryon density of (3.4±1.3)×10-5(l/15 Mpc)-1/2 cm-3, where l is the length of the filament along the line-of-sight. This density corresponds to a baryon over-density of ρ/<ρC> ≈150. The properties of the gas in the filament are consistent with results of simulations of the densest and hottest parts of the warm-hot intergalactic medium.
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