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

BSTRACT 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) × 10−14 erg cm−2 s−1 arcmin−2 in the 0.9-1.3 keV energy band for 1-keV plasma, which implies an electron density of ne= (4.7 ± 0.2) × 10−4 h1/2100 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. [ABSTRACT FROM AUTHOR]