Publications


The origin of radio emission in broad absorption line quasars: Results from the LOFAR Two-metre Sky Survey

ASTRONOMY & ASTROPHYSICS 622 (2019) ARTN A15

LK Morabito, JH Matthews, PN Best, G Gurkan, MJ Jarvis, I Prandoni, KJ Duncan, MJ Hardcastle, M Kunert-Bajraszewska, AP Mechev, S Mooney, J Sabater, HJA Rottgering, TW Shimwell, DJB Smith, C Tasse, WL Williams


Ultrahigh energy cosmic rays from shocks in the lobes of powerful radio galaxies

Monthly Notices of the Royal Astronomical Society 482 (2019) 4303-4321

JH Matthews, AR Bell, KM Blundell, AT Araudo

© 2018 The Author(s). The origin of ultrahigh energy cosmic rays (UHECRs) has been an open question for decades. Here, we use a combination of hydrodynamic simulations and general physical arguments to demonstrate that UHECRs can in principle be produced by diffusive shock acceleration (DSA) in shocks in the backflowing material of radio galaxy lobes. These shocks occur after the jet material has passed through the relativistic termination shock. Recently, several authors have demonstrated that highly relativistic shocks are not effective in accelerating UHECRs. The shocks in our proposed model have a range of non-relativistic or mildly relativistic shock velocities more conducive to UHECR acceleration, with shock sizes in the range 1–10 kpc. Approximately 10 per cent of jet’s energy flux is focused through a shock in the backflow of M > 3. Although the shock velocities can be low enough that acceleration to high energy via DSA is still efficient, they are also high enough for the Hillas energy to approach 10 19–20 eV, particularly for heavier CR composition and in cases where fluid elements pass through multiple shocks. We discuss some of the more general considerations for acceleration of particles to ultrahigh energy with reference to giant-lobed radio galaxies such as Centaurus A and Fornax A, a class of sources which may be responsible for the observed anisotropies from UHECR observatories.


Intrinsic rotation driven by turbulent acceleration

PLASMA PHYSICS AND CONTROLLED FUSION 61 (2019) ARTN 025003

M Barnes, FI Parra


The Quick and the Dead: Finding the Surviving Binary Companions of Galactic Supernovae with Gaia

ASTROPHYSICAL JOURNAL 871 (2019) ARTN 92

M Fraser, D Boubert


A Magellanic origin for the Virgo sub-structure

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 482 (2019) 4562-4569

D Boubert, V Belokurov, D Erkal, G Iorio


A hypervelocity star with a Magellanic origin

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 483 (2019) 2007-2013

D Erkal, D Boubert, A Gualandris, NW Evans, F Antonini


MADE: a spectroscopic mass, age, and distance estimator for red giant stars with Bayesian machine learning

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 484 (2019) 294-304

P Das, JL Sanders


$\texttt{stella}$: a mixed implicit-explicit, delta-f gyrokinetic code for general magnetic field configurations

Journal of Computational Physics Elsevier (2019)

M Barnes, F Parra-Diaz, M Landreman

Here we present details of a mixed implicit-explicit numerical scheme for the solution of the gyrokinetic-Poisson system of equations in the local limit. This scheme has been implemented in a new code called $\texttt{stella}$, which is capable of evolving electrostatic fluctuations with full kinetic electron effects and an arbitrary number of ion species in general magnetic geometry. We demonstrate the advantages of this mixed approach over a fully explicit treatment and provide linear and nonlinear benchmark comparisons for both axisymmetric and non-axisymmetric magnetic equilibria.


Orbit-superposition models of discrete, incomplete stellar kinematics: application to the Galactic centre

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2019)

J Magorrian

We present a method for fitting orbit-superposition models to the kinematics of discrete stellar systems when the available stellar sample has been filtered by a known selection function. The fitting method can be applied to any model in which the distribution function is represented as a linear superposition of basis elements with unknown weights. As an example, we apply it to Fritz et al.'s kinematics of the innermost regions of the Milky Way's nuclear stellar cluster. Assuming spherical symmetry, our models fit a black hole of mass $M_\bullet=(3.76\pm0.22)\times10^6\,M_\odot$, surrounded by an extended mass $M_\star=(6.57\pm0.54)\times10^6\,M_\odot$ within $4\,\pc$. Within $1\,\pc$ the best-fitting mass models have an approximate power-law density cusp $\rho\propto r^{-\gamma}$ with $\gamma=1.3\pm0.3$. We carry out an extensive investigation of how our modelling assumptions might bias these estimates: $M_\bullet$ is the most robust parameter and $\gamma$ the least. Internally the best-fitting models have broadly isotropic orbit distributions, apart from a bias towards circular orbits between 0.1 and 0.3 parsec.


A theoretical explanation for the Central Molecular Zone asymmetry

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 475 (2018) 2383-2402

MC Sormani, RG Tress, M Ridley, SCO Glover, RS Klessen, J Binney, J Magorrian, R Smith


Is the Milky Way still breathing? RAVE-Gaia streaming motions

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 475 (2018) 2679-2696

I Carrillo, I Minchev, G Kordopatis, M Steinmetz, J Binney, F Anders, O Bienayme, J Bland-Hawthorn, B Famaey, KC Freeman, G Gilmore, BK Gibson, EK Grebel, A Helmi, A Just, A Kunder, P McMillan, G Monari, U Munari, J Navarro, QA Parker, W Reid, G Seabroke, S Sharma, A Siebert, F Watson, J Wojno, RFG Wyse, T Zwitter


Confirming chemical clocks: asteroseismic age dissection of the Milky Way disc(s)

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 475 (2018) 5487-5500

VS Aguirre, M Bojsen-Hansen, D Slumstrup, L Casagrande, D Kawata, I Ciuca, R Handberg, MN Lund, JR Mosumgaard, D Huber, JA Johnson, MH Pinsonneault, AM Serenelli, D Stello, J Tayar, JC Bird, S Cassisi, M Hon, M Martig, PE Nissen, HW Rix, R Schonrich, C Sahlholdt, WH Trick, J Yu


The origin of the Gaia phase-plane spiral

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 481 (2018) 1501-1506

J Binney, R Schonrich


On the kinematics of a runaway Be star population

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 477 (2018) 5261-5278

D Boubert, NW Evans


Revisiting hypervelocity stars after Gaia DR2

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 479 (2018) 2789-2795

D Boubert, J Guillochon, K Hawkins, I Ginsburg, NW Evans, J Strader


intrinsic rotation driven by turbulent acceleration

Plasma Physics and Controlled Fusion IOP Publishing (2018)

MA BARNES, F Parra


Large-scale three-dimensional Gaussian process extinction mapping

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2018)

SE Sale, J Magorrian

Gaussian processes are the ideal tool for modelling the Galactic ISM, combining statistical flexibility with a good match to the underlying physics. In an earlier paper we outlined how they can be employed to construct three-dimensional maps of dust extinction from stellar surveys. Gaussian processes scale poorly to large datasets though, which put the analysis of realistic catalogues out of reach. Here we show how a novel combination of the Expectation Propagation method and certain sparse matrix approximations can be used to accelerate the dust mapping problem. We demonstrate, using simulated Gaia data, that the resultant algorithm is fast, accurate and precise. Critically, it can be scaled up to map the Gaia catalogue.


Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk.

Nature 555 (2018) 334-337

M Bergemann, B Sesar, JG Cohen, AM Serenelli, A Sheffield, TS Li, L Casagrande, KV Johnston, CFP Laporte, AM Price-Whelan, R Schönrich, A Gould

Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo-the faint, roughly spherical component of the Galaxy-reveals rich 'fossil' evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane-locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.


Self-inhibiting thermal conduction in a high-beta, whistler-unstable plasma

JOURNAL OF PLASMA PHYSICS 84 (2018) ARTN 905840305

S Komarov, AA Schekochihin, E Churazov, A Spitkovsky


Self-consistent modelling of our Galaxy with Gaia data

ASTROMETRY AND ASTROPHYSICS IN THE GAIA SKY 12 (2018) 111-118

J Binney

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