Forecasts for the detection of the magnetised cosmic web from cosmological simulations

Abstract

The cosmic web contains a large part of the total gas mass in the Universe, but it is difficult to detect at most wavelengths. Synchrotron emission from shock-accelerated electrons may offer the chance of imaging the cosmic web at radio wavelengths. In this work we use 3D cosmological ENZO-magnetohydrodynamic simulations (combined with a post-processing renormalisation of the magnetic field to bracket for missing physical ingredients and resolution effects) to produce models of the radio emission from the cosmic web. In post-processing we study the capabilities of 13 large radio surveys to detect this emission. We find that surveys by LOFAR, SKA1-LOW, and MWA have a chance of detecting the cosmic web, provided that the magnetisation level of the tenuous medium in filaments is of the order of ∼1% of the thermal gas energy.

Propagation of ultrahigh energy cosmic rays in extragalactic magnetic fields: a view from cosmological simulations

“…A subset of our simulations also made use of the recent porting of the Dedner algorithm onto CUDA (Li et al 2010), which runs ∼ 4 times faster on Graphics Processing Units (GPU), compared to the performance on CPUs. This suite of runs belongs to a larger suite of MHD cosmological simulations ("CHRONOS++"), designed to investigate the origin of extragalactic magnetic fields (Vazza et al 2014(Vazza et al , 2015.…”

“…This is expected, because efficient dynamo amplification within structures can develop only if the gas flow is turbulent enough, which requires much larger resolution (e. g. Cho et al 2009;Beresnyak & Miniati 2016). To overcome the limitations of resolution, similar to Vazza et al (2015), we renormalized the field strength of each cell in post-processing so that the magnetic field energy is 1% of the Vazza et al 2014). In order to bracket the uncertainties of where the small-scale dynamo process starts operating, we produced two versions of this run, by renormalising the magnetic energy wherever the gas density is ρcr,g (where ρcr,g is the critical gas density) or only limited to where the gas density is 50ρcr,g.…”

“…However, it shall be noticed that the validity of these lower limits is still subject to debate (see discussion in Broderick et al 2012). While future radio observations will have the chance to probe the magnetisation of cluster outskirts and filaments (e. g. Vazza et al 2015), the study of UHECRs has the unique potential to probe the magnetisation level of voids in the local Universe (and hence also the amplitude of primordial magnetic fields). Moreover, the possibility of limiting extragalactic magnetic fields outside clusters would also be crucial to assess the viability of axion-like particles as a candidate for dark matter because in the presence of significant magnetic fields they produce detectable effects on the spectrum of TeV sources (e. g. Horns et al 2012).…”

Clusters of Galaxies and the Cosmic Web with Square Kilometre Array

“…3). Simulations including magnetic field evolution along with the structure formation and radiative cooling can provide predictions for the radio emission from the large scale structure based on the recipes for production of relativistic electrons (Hoeft & Brüggen, 2007;Donnert et al, 2013;Vazza & Brüggen, 2014;Vazza et al, 2015b). It has been shown that a saturation of magnetisation can be achieved in a fully turbulent medium and there is near equipartition between the magnetic field and kinetic energy densities (e. g. Subramanian, Shukurov & Haugen, 2006;Iapichino & Brüggen, 2012).…”

“…A radio detection of filaments has been predicted in regions where magnetic field is about ∼10 -100 nG (Vazza et al, 2015a). Recent MHD simulations using EN ZO have predicted that a non-detection with the SKA can place constraints on the magnetic energy in the WHIM to be less than ∼ 1% of the thermal energy (Vazza et al, 2015b).…”