The ARTEMIS simulations: stellar haloes of Milky Way-mass galaxies

We introduce the Assembly of high-ResoluTion Eagle-simulations of MIlky Way-type galaxieS (ARTEMIS) simulations, a new set of 42 zoomed-in, high-resolution (baryon particle mass of ≈2×104M⊙h−1⁠), hydrodynamical simulations of galaxies residing in haloes of Milky Way mass, simulated with the EAGLE galaxy formation code with re-calibrated stellar feedback. In this study, we analyse the structure of stellar haloes, specifically the mass density, surface brightness, metallicity, colour, and age radial profiles, finding generally very good agreement with recent observations of local galaxies. The stellar density profiles are well fitted by broken power laws, with inner slopes of ≈−3, outer slopes of ≈−4, and break radii that are typically ≈20–40 kpc. The break radii generally mark the transition between in situ formation and accretion-driven formation of the halo. The metallicity, colour, and age profiles show mild large-scale gradients, particularly when spherically averaged or viewed along the major axes. Along the minor axes, however, the profiles are nearly flat, in agreement with observations. Overall, the structural properties can be understood by two factors: that in situ stars dominate the inner regions and that they reside in a spatially flattened distribution that is aligned with the disc. Observations targeting both the major and minor axes of galaxies are thus required to obtain a complete picture of stellar haloes

Informing dark matter direct detection limits with the ARTEMIS simulations

Dark matter (DM) direct detection experiments aim to place constraints on the DM--nucleon scattering cross-section and the DM particle mass. These constraints depend sensitively on the assumed local DM density and velocity distribution function. While astrophysical observations can inform the former (in a model-dependent way), the latter is not directly accessible with observations. Here we use the high-resolution ARTEMIS cosmological hydrodynamical simulation suite of 42 Milky Way-mass halos to explore the spatial and kinematical distributions of the DM in the solar neighbourhood, and we examine how these quantities are influenced by substructures, baryons, the presence of dark discs, as well as general halo-to-halo scatter (cosmic variance). We also explore the accuracy of the standard Maxwellian approach for modelling the velocity distribution function. We find significant halo-to-halo scatter in the density and velocity functions which, if propagated through the standard halo model for predicting the DM detection limits, implies a significant scatter about the typically quoted limit. We also show that, in general, the Maxwellian approximation works relatively well for simulations that include the important gravitational effects of baryons, but is less accurate for collisionless (DM-only) simulations. Given the significant halo-to-halo scatter in quantities relevant for DM direct detection, we advocate propagating this source of uncertainty through in order to derive conservative DM detection limits

Evolutionary Patterns of the Mitochondrial Genome in Metazoa: Exploring the Role of Mutation and Selection in Mitochondrial Protein–Coding Genes

The mitochondrial genome is a fundamental component of the eukaryotic domain of life, encoding for several important subunits of the respiratory chain, the main energy production system in cells. The processes by means of which mitochondrial DNA (mtDNA) replicates, expresses itself and evolves have been explored over the years, although various aspects are still debated. In this review, we present several key points in modern research on the role of evolutionary forces in affecting mitochondrial genomes in Metazoa. In particular, we assemble the main data on their evolution, describing the contributions of mutational pressure, purifying, and adaptive selection, and how they are related. We also provide data on the evolutionary fate of the mitochondrial synonymous variation, related to the nonsynonymous variation, in comparison with the pattern detected in the nucleus

The Relative Influence of Competition and Prey Defenses on the Phenotypic Structure of Insectivorous Bat Ensembles in Southern Africa

Deterministic filters such as competition and prey defences should have a strong influence on the community structure of animals such as insectivorous bats that have life histories characterized by low fecundity, low predation risk, long life expectancy, and stable populations. We investigated the relative influence of these two deterministic filters on the phenotypic structure of insectivorous bat ensembles in southern Africa. We used null models to simulate the random phenotypic patterns expected in the absence of competition or prey defences and analysed the deviations of the observed phenotypic pattern from these expected random patterns. The phenotypic structure at local scales exhibited non-random patterns consistent with both competition and prey defense hypotheses. There was evidence that competition influenced body size distribution across ensembles. Competition also influenced wing and echolocation patterns in ensembles and in functional foraging groups with high species richness or abundance. At the same time, prey defense filters influenced echolocation patterns in two species-poor ensembles. Non-random patterns remained evident even after we removed the influence of body size from wing morphology and echolocation parameters taking phylogeny into account. However, abiotic filters such as geographic distribution ranges of small and large-bodied species, extinction risk, and the physics of flight and sound probably also interacted with biotic filters at local and/or regional scales to influence the community structure of sympatric bats in southern Africa. Future studies should investigate alternative parameters that define bat community structure such as diet and abundance to better determine the influence of competition and prey defences on the structure of insectivorous bat ensembles in southern Africa

Prehospital transdermal glyceryl trinitrate in patients with ultra-acute presumed stroke (RIGHT-2): an ambulance-based, randomised, sham-controlled, blinded, phase 3 trial

Background High blood pressure is common in acute stroke and is a predictor of poor outcome; however, large trials of lowering blood pressure have given variable results, and the management of high blood pressure in ultra-acute stroke remains unclear. We investigated whether transdermal glyceryl trinitrate (GTN; also known as nitroglycerin), a nitric oxide donor, might improve outcome when administered very early after stroke onset. Methods We did a multicentre, paramedic-delivered, ambulance-based, prospective, randomised, sham-controlled, blinded-endpoint, phase 3 trial in adults with presumed stroke within 4 h of onset, face-arm-speech-time score of 2 or 3, and systolic blood pressure 120 mm Hg or higher. Participants were randomly assigned (1:1) to receive transdermal GTN (5 mg once daily for 4 days; the GTN group) or a similar sham dressing (the sham group) in UK based ambulances by paramedics, with treatment continued in hospital. Paramedics were unmasked to treatment, whereas participants were masked. The primary outcome was the 7-level modified Rankin Scale (mRS; a measure of functional outcome) at 90 days, assessed by central telephone follow-up with masking to treatment. Analysis was hierarchical, first in participants with a confirmed stroke or transient ischaemic attack (cohort 1), and then in all participants who were randomly assigned (intention to treat, cohort 2) according to the statistical analysis plan. This trial is registered with ISRCTN, number ISRCTN26986053. Findings Between Oct 22, 2015, and May 23, 2018, 516 paramedics from eight UK ambulance services recruited 1149 participants (n=568 in the GTN group, n=581 in the sham group). The median time to randomisation was 71 min (IQR 45–116). 597 (52%) patients had ischaemic stroke, 145 (13%) had intracerebral haemorrhage, 109 (9%) had transient ischaemic attack, and 297 (26%) had a non-stroke mimic at the final diagnosis of the index event. In the GTN group, participants’ systolic blood pressure was lowered by 5·8 mm Hg compared with the sham group (p<0·0001), and diastolic blood pressure was lowered by 2·6 mm Hg (p=0·0026) at hospital admission. We found no difference in mRS between the groups in participants with a final diagnosis of stroke or transient ischaemic stroke (cohort 1): 3 (IQR 2–5; n=420) in the GTN group versus 3 (2–5; n=408) in the sham group, adjusted common odds ratio for poor outcome 1·25 (95% CI 0·97–1·60; p=0·083); we also found no difference in mRS between all patients (cohort 2: 3 [2–5]; n=544, in the GTN group vs 3 [2–5]; n=558, in the sham group; 1·04 [0·84–1·29]; p=0·69). We found no difference in secondary outcomes, death (treatment-related deaths: 36 in the GTN group vs 23 in the sham group [p=0·091]), or serious adverse events (188 in the GTN group vs 170 in the sham group [p=0·16]) between treatment groups. Interpretation Prehospital treatment with transdermal GTN does not seem to improve functional outcome in patients with presumed stroke. It is feasible for UK paramedics to obtain consent and treat patients with stroke in the ultraacute prehospital setting. Funding British Heart Foundation

INFORMING DARK MATTER DETECTION EXPERIMENTS USING COSMOLOGICAL SIMULATIONS OF MILKY WAY-LIKE GALAXIES

Dark matter (DM) is one of the biggest mysteries in physics, a non-baryonic matter that accounts for ∼ 85% of all matter in the Universe. It plays a vital role in the formation and evolution of large-scale and galactic structures, yet its nature still remains unknown. Many DM candidates have be theorised, most notably the WIMPs, however without a confirmed detection numerous questions remain. Definitive evidence for the existence of WIMPs, or of any other DM candidates, is actively sought via both direct and indirect detection experiments. This thesis explores the effect of baryons and the uncertainties associated with direct and indirect DM detection using ARTEMIS, a new suite of high- resolution cosmological hydrodynamic simulations of Milky Way-like galaxies, to aid identification of DM. I begin by investigating the uncertainties associated with DM direct detection experi- ments, which aim to place constraints on the DM–nucleon scattering cross-section and the DM particle mass. These constraints depend sensitively on the assumed local DM density, the DM velocity distribution function, and several particle physics parameters. While astrophysical observations can measure the local DM density relatively accu- rately, the DM velocity distribution function is less well constrained. Using a sample of 42 Milky Way-mass halos from ARTEMIS, I explore the spatial and kinematical distributions of the DM in the simulated solar neighbourhoods, and study how these quantities are influenced by DM substructure, baryons, the presence of dark discs, as well as general halo-to-halo scatter (cosmic variance). I investigate also the accuracy of the Maxwellian approach for modelling velocity distribution functions in the standard halo model and find that this accuracy is hampered by significant halo-to-halo scatter in the (simulated) velocity functions. Allowing for this scatter in the computation of the iii DM detection limits in the standard halo model methodology leads to a significant scat- ter about the exclusion limit that is typically quoted. The Maxwellian approximation works relatively well for our simulations that include the baryons, but it is less accurate for collisionless (DM-only) simulations. Given the significant halo-to-halo scatter in the quantities relevant for DM direct detection, it is recommended that this source of uncertainty is propagated through in order to derive conservative DM detection limits. Using the ARTEMIS simulations, I then examine the prospects of indirect DM detec- tion in the Milky Way with the upcoming Cherenkov Telescope Array (CTA) using the specific instrumental sensitivity of this facility. I investigate the baryonic effects in the γ-ray luminosities and fluxes resulted from the DM annihilation in both central halos and substructure. The unresolved substructure in the simulations is taken into account via the commonly used ‘boost’ factor. However, I find that the boost factor depends not only on the cut-off mass value but, importantly, also on the assumed c−M relation which is used to determine the concentration of the subhalos. The simulations show that the DM annihilation luminosities and fluxes of the host halos are higher for the halos containing baryons. This is due to the higher densities and concentrations of these halos as a result of adiabatic contraction in the presence of baryons, with the DM subhalos less affected. Using these results, I investigated whether a nominal 50-hour observation with CTA would be sensitive enough to detect an annihilation signal from the central Milky Way DM halo and nearby subhalos. I find that the signal from main halos via either bb, tt or τ+τ− channels would be detectable, at energies ∼ 20 GeV −1 TeV. For CTA to detect an annihilation signal from subhalos their individual contributions must be summed. In that case, a possible detection from substructure can be at ener- gies ∼ 200 − 700 GeV via the τ+τ− annihilation channel. One of the largest sources of uncertainty in the differential γ-ray flux comes from the assumed c−M relation in calculating boost factors, which can lead to changes in fluxes by up to a factor of ∼ 10. The results show that predictions for direct and indirect detection experiments need to carefully consider the associated astrophysical uncertainties. Also, the impact of bary- onic physics on the DM in halos and subhalos is significant, emphasising the importance of using hydrodynamic simulations for making predictions for the detectability of DM