Globular clusters as probes of dark matter cusp-core transformations

Bursty star formation in dwarf galaxies can slowly transform a steep dark matter cusp into a constant density core. We explore the possibility that globular clusters (GCs) retain a dynamical memory of this transformation. To test this, we use the nbody6df code to simulate the dynamical evolution of GCs, including stellar evolution, orbiting in static and time-varying potentials for a Hubble time. We find that GCs orbiting within a cored dark matter halo, or within a halo that has undergone a cusp-core transformation, grow to a size that is substantially larger ($R_{\rm eff} > 10$ pc) than those in a static cusped dark matter halo. They also produce much less tidal debris. We find that the cleanest signal of an historic cusp-core transformation is the presence of large GCs with tidal debris. However, the effect is small and will be challenging to observe in real galaxies. Finally, we qualitatively compare our simulated GCs with the observed GC populations in the Fornax, NGC 6822, IKN and Sagittarius dwarf galaxies. We find that the GCs in these dwarf galaxies are systematically larger ($\langle R_{\rm eff}\rangle \simeq 7.8$ pc), and have substantially more scatter in their sizes, than in-situ metal rich GCs in the Milky Way and young massive star clusters forming in M83 ($\langle R_{\rm eff} \rangle \simeq 2.5$ pc). We show that the size, scatter and survival of GCs in dwarf galaxies are all consistent with them having evolved in a constant density core, or a potential that has undergone a cusp-core transformation, but not in a dark matter cusp.Comment: 14 pages, 10 figure

A polar surface eddy obscured by thermal stratification

Mesoscale and submesoscale eddies play an important role in the distribution of heat and biogeochemical properties throughout the global oceans. Such eddies are important in the Arctic Ocean, particularly in the frontal regions, but are difficult to detect using traditional satellite‐based methods. Here we use high‐resolution in situ data from an underwater glider to identify a surface eddy that was masked from remote‐sensing observations. We hypothesize that this masking was driven by thermal stratification driven by surface heat fluxes. The eddy was likely generated north of the Polar Front, before crossing the front and traveling south. We estimate that the observed eddy contained 4 × 1010 m3 of Arctic Water. The observation of this eddy, masked in satellite observations of sea surface temperature, suggests a historical underestimation of the prevalence and importance of eddies in this key mixing region. The water column of the Barents Sea, one of the circumpolar Arctic seas has a seemingly simple structure. In the south, warm Atlantic Water dominates; in the north, cold Arctic Water dominates; while at their boundary, the Arctic Water overlies the Atlantic Water. In the summer, the Arctic Water is largely devoid of the nutrients required to fuel the growth of phytoplankton, which is key to maintaining life in the ocean. In contrast, the Atlantic Water is one of the primary sources of nutrient‐rich water into the Arctic. In this study, we have used an underwater robotic instrument to identify a patch of Arctic Water which has been shed from the Arctic sector of the Barents Sea into the Atlantic sector. This patch of water is seen to have lower phytoplankton concentrations than the surrounding water. Due to atmospheric heating of the surface, this patch would be indistinguishable from the surrounding Atlantic Water and so would be absent for satellite observations of sea surface temperature. We suggest that this temperature masking has meant that we have previously underestimated how much water is moved within these patches in the Arctic seas

New constraints on the mass of fermionic dark matter from dwarf spheroidal galaxies

Theoretical Physic

Shine a light: Under-ice light and its ecological implications in a changing Arctic Ocean

The Arctic marine ecosystem is shaped by the seasonality of the solar cycle, spanning from 24-h light at the sea surface in summer to 24-h darkness in winter. The amount of light available for under-ice ecosystems is the result of different physical and biological processes that affect its path through atmosphere, snow, sea ice and water. In this article, we review the present state of knowledge of the abiotic (clouds, sea ice, snow, suspended matter) and biotic (sea ice algae and phytoplankton) controls on the underwater light field. We focus on how the available light affects the seasonal cycle of primary production (sympagic and pelagic) and discuss the sensitivity of ecosystems to changes in the light field based on model simulations. Lastly, we discuss predicted future changes in under-ice light as a consequence of climate change and their potential ecological implications, with the aim of providing a guide for future research

Globular cluster systems and galaxy formation

Globular clusters are compact, gravitationally bound systems of up to a million stars. The GCs in the Milky Way contain some of the oldest stars known, and provide important clues to the early formation and continuing evolution of our Galaxy. More generally, GCs are associated with galaxies of all types and masses, from low-mass dwarf galaxies to the most massive early-type galaxies which lie in the centres of massive galaxy clusters. GC systems show several properties which connect tightly with properties of their host galaxies. For example, the total mass of GCs in a system scales linearly with the dark matter halo mass of its host galaxy. Numerical simulations are at the point of being able to resolve globular cluster formation within a cosmological framework. Therefore, GCs link a range of scales, from the physics of star formation in turbulent gas clouds, to the large-scale properties of galaxies and their dark matter. In this Chapter we review some of the basic observational approaches for GC systems, some of their key observational properties, and describe how GCs provide important clues to the formation of their parent galaxies.Comment: 32 pages, 6 figures. Accepted for publication in the book "Reviews in Frontiers of Modern Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka; publisher Springer Nature) funded by the European Union Erasmus+ Strategic Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556

North Isles local plan Sanday and North Ronaldsay

SIGLELD:3423.78(3) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Atlantic inflow is the primary driver of remotely sensed autumn blooms in the Barents Sea

Arctic shelf seas have historically hosted a single spring bloom, contrasting with temperate seas, where additional smaller autumn blooms occur regularly, caused by storm systems mixing nutrient-rich deep waters towards the surface ocean. Post millennium, autumn blooms have increased in frequency in Arctic shelf seas. Delayed sea-ice formation, stronger autumn winds and greater inflows of nutrient-rich temperate waters have all been suggested to support growing annual net primary production and an increasing incidence of autumn blooms. Here, we investigated data sets of remotely sensed September chlorophyll a, sea surface temperature, current and wind speeds. We explored mechanistic drivers of autumn blooms in the Barents Sea, one of the most productive Arctic shelf seas, to better understand the role of strong winds and the ingression of Atlantic waters in the dynamics of autumn blooms. We performed geographically resolved regressions between remotely sensed September chlorophyll a and environmental conditions in the Barents Sea, demonstrating a strong dependency of autumn bloom intensity on Atlantic inflow. This result highlights the importance of increased study of autumn phytoplankton bloom dynamics on Arctic shelf seas, especially the further collection and dissemination of in situ cell count and nutrient data to determine the significance of autumn blooms for wider ecosystem function

Exploiting the enemy in the Orkneys : the employment of Italian prisoners of war on the Scapa Flow barriers during the Second World War

The British naval base at Scapa Flow in the Orkneys played a vital role during the Second World War for the Allied war effort. It housed the British Home Fleet and provided a strategic military base for Allied operations in the North Sea, Atlantic and the Arctic. Although Scapa Flow’s military history is well served, the barriers built by Italian prisoners of war (POWs) to strengthen its defences in the early war years have received little attention.1 Britain faced a peculiar dilemma in the Orkneys: defences needed to be fortified given Scapa Flow’s key location and military role, but manpower was extremely scarce. Civilians were reluctant to work on the islands due to harsh and dangerous working conditions. Since efforts to attract them via compulsion and bonus schemes, and to employ migrant workers were insufficient, the government employed 1,200 Italian POWs instead, despite the scheme’s doubtful legality under the Geneva Convention. This article examines the history and significance of the Italians’ employment in the Orkneys and demonstrates that their contribution was vital for the construction of the Churchill barriers. Previous studies have neglected the multiple strikes by the prisoners and their protests against illegal work and some wrongly assume that the prisoners were not participating in the construction of the barriers. This article explicitly examines the legality issue and the prisoners’ extensive employment. Although their employment violated the Geneva Convention, British authorities and neutral delegates deemed it legal, thus securing the barriers’ completion