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

TL;DR

This study estimates the electron density in galaxy filaments at z~0.1 by analyzing stacked X-ray data from a large filament sample, providing new insights into their physical properties.

Contribution

It presents the first large-scale X-ray analysis of galaxy filaments to determine their typical electron density and examines the effect of supercluster membership.

Findings

Detected faint X-ray surface brightness from filaments.

Estimated electron density of about 4.7 x 10^{-4} cm^{-3}.

Unclear impact of supercluster membership on electron density.

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 Pimbblet et al.'s (2004) filament catalogue, which is in turn sourced from the 2 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) x 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) x 10^{-4} h_{100}^{1/2} cm^{-3}. Finally, we examine if a filament's membership to a supercluster leads to an enhanced electron density as reported by Kull & Bohringer (1999). We suggest it remains unclear if supercluster membership causes such an enhancement.