Simulations of ultra-high energy cosmic rays in the local Universe and the origin of cosmic magnetic fields

We simulate the propagation of cosmic rays at ultra-high energies, ≳1018 eV, in models of extragalactic magnetic fields in constrained simulations of the local Universe. We use constrained initial conditions with the cosmological magnetohydrodynamics code ENZO. The resulting models of the distribution of magnetic fields in the local Universe are used in the CRPROPA code to simulate the propagation of ultra-high energy cosmic rays. We investigate the impact of six different magneto-genesis scenarios, both primordial and astrophysical, on the propagation of cosmic rays over cosmological distances. Moreover, we study the influence of different source distributions around the Milky Way. Our study shows that different scenarios of magneto-genesis do not have a large impact on the anisotropy measurements of ultra-high energy cosmic rays. However, at high energies above the Greisen–Zatsepin–Kuzmin (GZK)-limit, there is anisotropy caused by the distribution of nearby sources, independent of the magnetic field model. This provides a chance to identify cosmic ray sources with future full-sky measurements and high number statistics at the highest energies. Finally, we compare our results to the dipole signal measured by the Pierre Auger Observatory. All our source models and magnetic field models could reproduce the observed dipole amplitude with a pure iron injection composition. Our results indicate that the dipole is observed due to clustering of secondary nuclei in direction of nearby sources of heavy nuclei. A light injection composition is disfavoured, since the increase in dipole angular power from 4 to 8 EeV is too slow compared to observation by the Pierre Auger Observatory

The Launching of Cold Clouds by Galaxy Outflows III: The Influence of Magnetic Fields

Motivated by observations of outflowing galaxies, we investigate the combined impact of magnetic fields and radiative cooling on the evolution of cold clouds embedded in a hot wind. We perform a collection of three-dimensional adaptive mesh refinement, magnetohydrodynamical simulations that span two resolutions, and include fields that are aligned and transverse to the oncoming, super-Alfv\'enic material. Aligned fields have little impact on the overall lifetime of the clouds over the non-magnetized case, although they do increase the mixing between the wind and cloud material by a factor of $\approx 3.$ Transverse fields lead to magnetic draping, which isolates the clouds, but they also squeeze material in the direction perpendicular to the field lines, which leads to rapid mass loss. A resolution study suggests that the magnetized simulations have somewhat better convergence properties than non-magnetized simulations, and that a resolution of 64 zones per cloud radius is sufficient to accurately describe these interactions. We conclude that the combined effects of radiative cooling and magnetic fields are dependent on field orientation, but are unlikely to enhance cloud lifetimes beyond the effect of radiative cooling alone.Comment: 15 pages, 14 figures, accepted to Ap

The redshift evolution of extragalactic magnetic fields

Faraday rotation studies of distant radio sources can constrain the evolution and the origin of cosmic magnetism. We use data from the LOFAR Two Metre Sky Survey: Data Release 2 (LoTSS DR2) to study the dependence of the Faraday rotation measure (RM) on redshift. By focusing on radio sources that are close in terms of their projection on the sky, but physically unrelated (random pairs), we measure the RM difference, $\Delta$RM, between the two sources. Thus, we isolate the extragalactic contribution to $\Delta$RM from other contributions. We present a statistical analysis of the resulting sample of random pairs and find a median absolute RM difference |$\Delta$RM| $= (1.79 \pm 0.09)$ rad/m$^{2}$ , with |$\Delta$RM| uncorrelated both with respect to the redshift difference of the pair and the redshift of the nearer source, and a median excess of random pairs over physical pairs of $(1.65 \pm 0.10)$ rad/m$^{2}$. We seek to reproduce this result with Monte Carlo simulations assuming a non vanishing seed cosmological magnetic field and a redshift evolution of the comoving magnetic field strength that varies as $1/(1 + z)^{\gamma}$. We find the best fitting results $B_0 \equiv B_{\rm comoving}(z = 0) \lesssim (2.0 \pm 0.2)$ nG and $\gamma \lesssim 4.5 \pm 0.2$ that we conservatively quote as upper limits due to an unmodelled but non vanishing contribution of local environments to the RM difference. A comparison with cosmological simulations shows our results to be incompatible with primordial magnetogenesis scenarios with uniform seed fields of order nG

Development of a model for anemia of inflammation that is relevant to critical care

Background: Anemia of inflammation (AI) is common in critically ill patients. Although this syndrome negatively impacts the outcome of critical illness, understanding of its pathophysiology is limited. Also, new therapies that increase iron availability for erythropoiesis during AI are upcoming. A model of AI induced by bacterial infections that are relevant for the critically ill is currently not available. This paper describes the development of an animal model for AI that is relevant for critical care research. Results: In experiments with rats, the rats were inoculated either repeatedly or with a slow release of Streptococcus pneumoniae or Pseudomonas aeruginosa. Rats became ill, but their hemoglobin levels remained stable. The use of a higher dose of bacteria resulted in a lethal model. Then, we turned to a model with longer disease duration, using pigs that were supported by mechanical ventilation after inoculation with P. aeruginosa. The pigs became septic 12 to 24 h after inoculation, with a statistically significant decrease in mean arterial pressure and base excess, while heart rate tended to increase. Pigs needed resuscitation and vasopressor therapy to maintain a mean arterial pressure > 60 mmHg. After 72 h, the pigs developed anemia (baseline 9.9 g/dl vs. 72 h, 7.6 g/dl, p = 0.01), characterized by statistically significant decreased iron levels, decreased transferrin saturation, and increased ferritin. Hepcidin levels tended to increase and transferrin levels tended to decrease. Conclusions: Using pathogens commonly involved in pulmonary sepsis, AI could not be induced in rats. Conversely, in pigs, P. aeruginosa induced pulmonary sepsis with concomitant AI. This AI model can be applied to study the pathophysiology of AI in the critically ill and to investigate the effectivity and toxicity of new therapies that aim to increase iron availability. Keywords: Anemia of inflammation; Animal model; ICU; Infection; Iron

Merging Cluster Collaboration:Optical and Spectroscopic Survey of a Radio-Selected Sample of Twenty Nine Merging Galaxy Clusters

Multi-band photometric and multi-object spectroscopic surveys of merging galaxy clusters allow for the characterization of the distributions of constituent dark matter and galaxy populations, constraints on the dynamics of the merging subclusters, and an understanding of galaxy evolution of member galaxies. We present deep photometric observations from Subaru/SuprimeCam and a catalog of $\sim$5400 spectroscopic cluster members from Keck/DEIMOS across 29 merging galaxy clusters ranging in redshift from $z=0.07$ to $0.55$. The ensemble is compiled based on the presence of radio relics, which highlight cluster scale collisionless shocks in the intra-cluster medium. Together with the spectroscopic and photometric information, the velocities, timescales, and geometries of the respective merging events may be tightly constrained. In this preliminary analysis, the velocity distributions of 28 of the 29 clusters are shown to be well fit by single Gaussians. This indicates that radio relic mergers largely occur transverse to the line of sight and/or near apocenter. In this paper, we present our optical and spectroscopic surveys, preliminary results, and a discussion of the value of radio relic mergers for developing accurate dynamical models of each system