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

• Published in: Monthly notices of the Royal Astronomical Society 2011-08, Vol.415 (2), p.1961-1966
• Main Authors: Fraser-McKelvie, Amelia, Pimbblet, Kevin A., Lazendic, Jasmina S.
• Format: Article
• Language: English
• Subjects: Astronomy; cosmology: observations; Earth, ocean, space; Electrons; Exact sciences and technology; galaxies: clusters: general; large-scale structure of Universe; Red shift; Stars & galaxies; X-ray astronomy; X-rays: general
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2011.18847.x

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 n e= (4.7 ± 0.2) × 10−4 h 1/2 100 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.