| 1. |
- Govoni, F., et al.
(författare)
-
A radio ridge connecting two galaxy clusters in a filament of the cosmic web
- 2019
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6444, s. 981-984
-
Tidskriftsartikel (refereegranskat)abstract
- Galaxy clusters are the most massive gravitationally bound structures in the Universe. They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the intracluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low-Frequency Array (LOFAR) telescope network at 140 megahertz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may reaccelerate a preexisting population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge.
|
|
| 2. |
- Weltman, A., et al.
(författare)
-
Fundamental physics with the Square Kilometre Array
- 2020
-
Ingår i: Publications Astronomical Society of Australia. - : CAMBRIDGE UNIV PRESS. - 1323-3580 .- 1448-6083. ; 37
-
Forskningsöversikt (refereegranskat)abstract
- The Square Kilometre Array (SKA) is a planned large radio interferometer designed to operate over a wide range of frequencies, and with an order of magnitude greater sensitivity and survey speed than any current radio telescope. The SKA will address many important topics in astronomy, ranging from planet formation to distant galaxies. However, in this work, we consider the perspective of the SKA as a facility for studying physics. We review four areas in which the SKA is expected to make major contributions to our understanding of fundamental physics: cosmic dawn and reionisation; gravity and gravitational radiation; cosmology and dark energy; and dark matter and astroparticle physics. These discussions demonstrate that the SKA will be a spectacular physics machine, which will provide many new breakthroughs and novel insights on matter, energy, and spacetime.
|
|
| 3. |
- Heald, G., et al.
(författare)
-
Magnetism science with the square kilometre array
- 2020
-
Ingår i: Galaxies. - : MDPI AG. - 2075-4434. ; 8:8
-
Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as diverse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.
|
|
| 4. |
- Mereaux, JL, et al.
(författare)
-
Increasing involvement of CAPN1 variants in spastic ataxias and phenotype-genotype correlations
- 2021
-
Ingår i: Neurogenetics. - : Springer Science and Business Media LLC. - 1364-6753 .- 1364-6745. ; 22:1, s. 71-79
-
Tidskriftsartikel (refereegranskat)abstract
- Spastic ataxias are rare neurogenetic disorders involving spinocerebellar and pyramidal tracts. Many genes are involved. Among them, CAPN1, when mutated, is responsible for a complex inherited form of spastic paraplegia (SPG76). We report the largest published series of 21 novel patients with nine new CAPN1 disease-causing variants and their clinical characteristics from two European university hospitals (Paris and Stockholm). After a formal clinical examination, causative variants were identified by next-generation sequencing and confirmed by Sanger sequencing. CAPN1 variants are a rare cause (~ 1.4%) of young-adult-onset spastic ataxia; however, together with all published cases, they allowed us to better describe the clinical and genetic spectra of this form. Truncating variants are the most frequent, and missense variants lead to earlier age at onset in favor of an additional deleterious effect. Cerebellar ataxia with cerebellar atrophy, dysarthria and lower limb weakness are often associated with spasticity. We also suggest that cognitive impairment and depression should be assessed specifically in the follow-up of SPG76 cases.
|
|
| 5. |
- O'Sullivan, S. P., et al.
(författare)
-
New constraints on the magnetization of the cosmic web using LOFAR Faraday rotation observations
- 2020
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 495:3, s. 2607-2619
-
Tidskriftsartikel (refereegranskat)abstract
- Measuring the properties of extragalactic magnetic fields through the effect of Faraday rotation provides a means to understand the origin and evolution of cosmic magnetism. Here we use data from the LOFAR Two-Metre Sky Survey (LoTSS) to calculate the Faraday rotation measure (RM) of close pairs of extragalactic radio sources. By considering the RM difference (Delta RM) between physical pairs (e.g. double-lobed radio galaxies) and non-physical pairs (i.e. close projected sources on the sky), we statistically isolate the contribution of extragalactic magnetic fields to Delta RM along the line of sight between non-physical pairs. From our analysis, we find no significant difference between the ?RM distributions of the physical and non-physical pairs, limiting the excess Faraday rotation contribution to <1.9 rad/m(2) (similar to 95% confidence). We use this limit with a simple model of an inhomogeneous universe to place an upper limit of 4 nG on the cosmological co-moving magnetic field strength on Mpc scales. We also compare the RM data with a more realistic suite of cosmological MHD simulations, that explore different magnetogenesis scenarios. Both magnetization of the large scale structure by astrophysical processes such as galactic and AGN outflows, and simple primordial scenarios with seed magnetic field strengths <0.5 nG cannot be rejected by the current data; while stronger primordial fields or models with dynamo amplification in filaments are disfavoured.
|
|
| 6. |
- O'Sullivan, Shane P., et al.
(författare)
-
The intergalactic magnetic field probed by a giant radio galaxy
- 2019
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 622
-
Forskningsöversikt (refereegranskat)abstract
- Cosmological simulations predict that an intergalactic magnetic field (IGMF) pervades the large scale structure (LSS) of the Universe. Measuring the IGMF is important to determine its origin (i.e. primordial or otherwise). Using data from the LOFAR Two Metre Sky Survey (LoTSS), we present the Faraday rotation measure (RM) and depolarisation properties of the giant radio galaxy J1235+5317, at a redshift of z = 0.34 and 3.38 Mpc in size. We find a mean RM difference between the lobes of 2.5 ±0.1 rad m -2 , in addition to small scale RM variations of ∼0.1 rad m -2 . From a catalogue of LSS filaments based on optical spectroscopic observations in the local universe, we find an excess of filaments intersecting the line of sight to only one of the lobes. Associating the entire RM difference to these LSS filaments leads to a gas density-weighted IGMF strength of ∼0.3 μG. However, direct comparison with cosmological simulations of the RM contribution from LSS filaments gives a low probability (∼5%) for an RM contribution as large as 2.5 rad m -2 , for the case of IGMF strengths of 10-50 nG. It is likely that variations in the RM from the Milky Way (on 11′ scales) contribute significantly to the mean RM difference, and a denser RM grid is required to better constrain this contribution. In general, this work demonstrates the potential of the LOFAR telescope to probe the weak signature of the IGMF. Future studies, with thousands of sources with high accuracy RMs from LoTSS, will enable more stringent constraints on the nature of the IGMF.
|
|
| 7. |
- Pomakov, V. P., et al.
(författare)
-
The redshift evolution of extragalactic magnetic fields
- 2022
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 515:1, s. 256-270
-
Tidskriftsartikel (refereegranskat)abstract
- 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, ΔRM, between the two sources. Thus, we isolate the extragalactic contribution to ΔRM from other contributions. We present a statistical analysis of the resulting sample of random pairs and find a median absolute RM difference |ΔRM| =(1.79 ± 0.09) rm rad, m-2, with |ΔRM| 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 ± 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 + z)-γ. We find the best-fitting results B0 Bcomoving(z = 0) (2.0 ± 0.2) nG and γ 4.5 ± 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.
|
|
| 8. |
- Vazza, F., et al.
(författare)
-
Electron and proton acceleration efficiency by merger shocks in galaxy clusters
- 2015
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 451:2, s. 2198-2211
-
Tidskriftsartikel (refereegranskat)abstract
- Radio relics in galaxy clusters are associated with powerful shocks that (re) accelerate relativistic electrons. It is widely believed that the acceleration proceeds via diffusive shock acceleration. In the framework of thermal leakage, the ratio of the energy in relativistic electrons to the energy in relativistic protons should be smaller than K-e/p similar to 10(-2). The relativistic protons interact with the thermal gas to produce gamma-rays in hadronic interactions. Combining observations of radio relics with upper limits from gamma-ray observatories can constrain the ratio K-e/p. In this work, we selected 10 galaxy clusters that contain double radio relics, and derive new upper limits from the stacking of gamma-ray observations by Fermi. We modelled the propagation of shocks using a semi-analytical model, where we assumed a simple geometry for shocks and that cosmic ray protons are trapped in the intracluster medium. Our analysis shows that diffusive shock acceleration has difficulties in matching simultaneously the observed radio emission and the constraints imposed by Fermi, unless the magnetic field in relics is unrealistically large (>> 10 mu G). In all investigated cases (also including realistic variations of our basic model and the effect of re-acceleration), the mean emission of the sample is of the order of the stacking limit by Fermi, or larger. These findings put tension on the commonly adopted model for the powering of radio relics, and imply that the relative acceleration efficiency of electrons and protons is at odds with predictions of diffusive shock acceleration, requiring K-e/p >= 10 - 10(-2).
|
|
