An estimate of the electron density in filaments of galaxies at z ~ 0.1

Abstract

Most of the baryons in the Universe are thought to be contained within filaments of galaxies, but as yet, no single study has published the observed properties of a large sample of known filaments to determine typical physical characteristics such as temperature and electron density. This paper presents a comprehensive large-scale search conducted for X-ray emission from a population of 41 bona fide filaments of galaxies to determine their X-ray flux and electron density. The sample is generated from the filament catalogue of Pimbblet et al., which is in turn sourced from the two-degree Field Galaxy Redshift Survey (2dFGRS). Since the filaments are expected to be very faint and of very low density, we used stacked ROSAT All-Sky Survey data. We detect a net surface brightness from our sample of filaments of (1.6 ± 0.1) × 10-14ergcm-2s-1arcmin-2 in the 0.9-1.3keV energy band for 1-keV plasma, which implies an electron density of ne= (4.7 ± 0.2) × 10-4h1/2100 cm-3. Finally, we examine if a filament's membership to a supercluster leads to an enhanced electron density as reported by Kull & Böhringer. We suggest it remains unclear if supercluster membership causes such an enhancement. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.