Cluster magnetic fields from galactic outflows

Abstract

We performed cosmological, magnetohydrodynamical simulations to follow the evolution of magnetic fields in galaxy clusters, exploring the possibility that the origin of the magnetic seed fields is galactic outflows during the starburst phase of galactic evolution. To do this, we coupled a semi‐analytical model for magnetized galactic winds as suggested by Bertone, Vogt & Enßlin to our cosmological simulation. We find that the strength and structure of magnetic fields observed in galaxy clusters are well reproduced for a wide range of model parameters for the magnetized, galactic winds and do only weakly depend on the exact magnetic structure within the assumed galactic outflows. Although the evolution of a primordial magnetic seed field shows no significant differences to that of galaxy cluster fields from previous studies, we find that the magnetic field pollution in the diffuse medium within filaments is below the level predicted by scenarios with pure primordial magnetic seed field. We therefore conclude that magnetized galactic outflows and their subsequent evolution within the intracluster medium can fully account for the observed magnetic fields in galaxy clusters. Our findings also suggest that measuring cosmological magnetic fields in low‐density environments such as filaments is much more useful than observing cluster magnetic fields to infer their possible origin.

Limiting magnetic fields in the cosmic web with diffuse radio emission

“…Blasi et al 2007), and 2) the number density of these CRe ± should be low in filaments, so using this model should produce a conservative upper limit on the magnetic fields. Donnert et al (2009) used different models for seeding the magnetic fields at high redshift, and traced the amplification of these fields during the collapse of the local structures. These simulations have been used to model the giant radio halo of the Coma cluster (Donnert et al 2009), Faraday rotation from the local cosmic web (Stasyszyn et al 2010, also through cross-correlation), and the origin of fast radio bursts (FRBs, Dolag et al 2015).…”

“…Figure 2. Plot of average magnitude of magnetic field as a function of fractional density for the models used by Dolag et al (2004Dolag et al ( , 2005 and Donnert et al (2009). This work focuses on the cosmological model, which predicts the highest values within filaments.…”

“…If this plasma is detected at radio wavelengths, it can constrain the origin of the large-scale magnetic fields that permeate the intergalactic medium of galaxy clusters (see Brunetti & Jones 2014, for a review), differentiating, e.g., between the interaction of radio and star-forming galaxies with the WHIM (e.g. Donnert et al 2009) and a primordial magnetic field (Marinacci et al 2015). Observationally inferring the presence of magnetic (B) fields outside of dense clusters of galaxies is extremely difficult (e.g.…”

“…Observationally inferring the presence of magnetic (B) fields outside of dense clusters of galaxies is extremely difficult (e.g. Xu et al 2006), and B field estimates from simulations can vary from 0.2 µG (Cho & Ryu 2009) to 0.005 µG (Donnert et al 2009), depending on the models used for seeding and amplifying the fields. Any measurement of these currently unconstrained values would provide a useful constraint for differentiating between the possible models.…”

UHECR observations and lensing in the magnetic field of the Virgo cluster

“…Although our understanding of their origin is still limited, at present, numerical simulations which follow the amplification of weak magnetic seed fields by structure formation lead to a consistent picture of the predicted magnetic field and its structure within galaxy clusters [13,14,16,17], well in line with the observed Faraday rotation signal. It is worth mentioning that the predicted magnetic field structure within galaxy clusters is found to not depend on details within the structures of the magnetic seed fields and therefore can be assumed to be independent on the exact mechanism which creates the magnetic seed field at high redshift [13,15].…”