SIMBAD references

Clusters of galaxies are often located at the intersections of long filaments of galaxies, and numerical simulations of structure formation indicate that these filaments contain not only dark matter and galaxies but also moderately hot gas. Hence the filaments might be visible in X-rays if they contain sufficiently dense gas. Data from the ROSAT All-Sky Survey were used to search for X-ray emission from such filaments connecting clusters. We do not find any filament emission. The 2-sigma upper limit for a 1keV plasma is 3.9x10^–16erg/cm²/s/arcmin² in the 0.5 to 2.0keV energy band. This upper limit yields an upper limit on the filament electron density comparable to that found in some large scale structure models. We conclude that the new extended cluster component, found in a region of the ROSAT All-Sky Survey by cross-correlating its background fluctuations with the Abell cluster catalogue, is not confined to filaments connecting clusters.