A Filament between Galaxy Clusters A3391 and A3395

Abstract

Filamentary gas spanning the region between the galaxy clusters Abell 3391 and Abell 3395 has been detected using ASCA and ROSAT archived data. The gas has a minimum Ñux of 1.3 ] 10~12 ergs cm~2 s~1 (0.8È10 keV). Within this Ðlament resides a galaxy group for which a Ñux of (2.0^0.3) ] 10~13 ergs cm~2 s~1 (0.8È10 keV) is determined. An analysis using ray-tracing determines light scattered into the Ðlamentary region contributes 13% of the count rate. The structure in which the Ðlamentary gas resides is postulated to be a Ðlament aligned nearly lengthwise with the line of sight. IdentiÐcation of this structure as a Ðlament is based on the angular and redshift distribution of surrounding galaxies and clusters. The distribution is compatible with the structure being a quasi-linear structure tilted to the line of sight such that the ratio of the depth to the tangential distance is between 6 : 1 and 18 : 1. The Ðlamentary gas contains on the order of 1013 of gas, which is close to 2% of the total mass of the system. M _ Subject headings : galaxies : clusters : individual (A3391, A3395) È large-scale structure of universe È X-rays : di †use background È X-rays : galaxies : clusters

Where Are the Baryons? III. Nonequilibrium Effects and Observables

“…The reality of the WHIM has now been quite convincingly confirmed by a number of observations from the Hubble Space Telescope, the Far Ultraviolet Spectroscopic Explorer, Chandra, and XMM-Newton Oegerle et al 2000;Scharf et al 2000;Tittley & Henriksen 2001;Savage et al 2002;Fang et al 2002b;Nicastro et al 2002;Mathur et al 2003;Kaastra et al 2003;Finoguenov et al 2003;Sembach et al 2004;Nicastro et al 2005).…”

Planckintermediate results

“…Indeed, the integrated Compton parameter in the intercluster region is Y = (4.5 ± 0.7) × 10 −3 (arcminutes) 2 -of the same order of magnitude as that for the A399-A401 pair (see below). However, this residual is suspiciously close to the NW component of the A3395 cluster that was discussed in Tittley & Henriksen (2001) (and not included in our model), indicating that a far more complex model is necessary to subtract the cluster components. We can also notice in the figure the contribution from a radio point-source that appears as a decrement in the reconstructed Compton parameter map.…”

“…The quality of the X-ray data is significantly poorer than in the case of A399-A401 (less than half the amount of exposure time), making it difficult to distinguish between background and diffuse X-rays in the intercluster region. Moreover, the clusters that form the system A3395 are clearly elongated (this is even clearer when studying XMM-Newton and Chandra images of the cluster, see for example Tittley & Henriksen 2001), which adds another complication to the model. For the SZ part of the data, even though there seems to be a signal in the intercluster region, the modelling of the SZ signal from A3395 is affected because Planck cannot resolve the individual subsystems in A3395.…”

“…A3395 is a multiple system formed of at least three identified clusters (see Tittley & Henriksen 2001). For the purpose of this paper we considered the two clusters most important in X-rays (SW and E), which can be clearly identified in Fig.…”

“…There is also evidence of filamentary structure in the intercluster region from X-ray observations of several well-known merging cluster pairs such as A222-A223 (Werner et al 2008), A399-A401 (Sakelliou & Ponman 2004), A3391-A3395 (Tittley & Henriksen 2001), and from the double cluster A1758 (Durret et al 2011). The pairs of clusters A3391-A3395 (separated by about 50 on the sky and at redshifts z = 0.051 and z = 0.057, respectively, Tittley & Henriksen 2001) and more specially, A399-A401 (separated by about 40 on the sky and at redshifts z = 0.0724 and z = 0.0737, respectively) are of particular interest for the purpose of this paper, given their geometry and angular separation. This is sufficient to allow Planck to resolve the individual cluster components.…”