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

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

Abstract

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

SIMBAD Objects -- not yet in SIMBAD

Contents

• 1. Introduction
• 2. Significance and contouring
• 3. The effect of the PSF
• 4. Data and simulations
  • 4.1. Mrk 474
  • 4.2. NGC 4651/3C 275.1
  • 4.3. NGC 3067/3C 232
  • 4.4. NGC 4319/Mrk 205
  • 4.5. NGC 3628
  • 4.6. NGC 4151
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000
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