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Astron. Astrophys. 357, 884-890 (2000)

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Determining the reality of X-ray filaments

M.J. Hardcastle

University of Bristol, Department of Physics, Tyndall Avenue, Bristol BS8 1TL, UK (m.hardcastle@bristol.ac.uk)

Received 29 December 1999 / Accepted 11 April 2000


A number of authors have reported filaments connecting bright structures in high-resolution X-ray images, and in some cases these have been taken as evidence for a physical connection between the structures, which might be thought to provide support for a model with non-cosmological redshifts. In this Paper I point out two problems which are inherent in the interpretation of smoothed photon-limited data of this kind, and develop some simple techniques for the assessment of the reality of X-ray filaments, which can be applied to either simply smoothed or adaptively smoothed data. To illustrate the usefulness of these techniques, I apply them to archival ROSAT observations of galaxies and quasars previously analysed by others. I show that several reported filamentary structures connecting X-ray sources are not in fact significantly detected.

Key words: methods: statistical – X-rays: galaxies – galaxies: Seyfert – galaxies: quasars: general – galaxies: starburst

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000