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


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


Lessons from the curious case of the ‘fastest’ star in Gaia DR2

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 486 (2019) 2618-2630

D Boubert, J Strader, D Aguado, G Seabroke, SE Koposov, JL Sanders, S Swihart, L Chomiuk, NW Evans


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 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.


The luminosity dependence of thermally driven disc winds in low-mass X-ray binaries

Monthly Notices of the Royal Astronomical Society 484 (2019) 4635-4644

N Higginbottom, C Knigge, KS Long, JH Matthews, EJ Parkinson

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. We have carried out radiation-hydrodynamic simulations of thermally driven accretion disc winds in low-mass X-ray binaries. Our main goal is to study the luminosity dependence of these outflows and compare with observations. The simulations span the range 0.04 ≤ L acc /L Edd ≤ 1.0 and therefore cover most of the parameter space in which disc winds have been observed. Using a detailed Monte Carlo treatment of ionization and radiative transfer, we confirm two key results found in earlier simulations that were carried out in the optically thin limit: (i) the wind velocity - and hence the maximum blueshift seen in wind-formed absorption lines - increases with luminosity; (ii) the large-scale wind geometry is quasi-spherical, but observable absorption features are preferentially produced along high-column equatorial sightlines. In addition, we find that (iii) the wind efficiency always remains approximately constant at skew4dotM-rm wind/skew4dotM-rm acc simeq 2, a behaviour that is consistent with observations. We also present synthetic Fe xxv and Fe xxvi absorption line profiles for our simulated disc winds in order to illustrate the observational implications of our results.


A hybrid gyrokinetic ion and isothermal electron fluid code for astrophysical plasma

JOURNAL OF COMPUTATIONAL PHYSICS 360 (2018) 57-73

Y Kawazura, M Barnes


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


The origin of the Gaia phase-plane spiral

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

J Binney, R Schonrich


Isochrone ages for ∼3 million stars with the second Gaia data release

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 481 (2018) 4093-4110

JL Sanders, P Das


Three Hypervelocity White Dwarfs in Gaia DR2: Evidence for Dynamically Driven Double-degenerate Double-detonation Type Ia Supernovae

ASTROPHYSICAL JOURNAL 865 (2018) ARTN 15

KJ Shen, D Boubert, BT Gansicke, SW Jha, JE Andrews, L Chomiuk, RJ Foley, M Fraser, M Gromadzki, J Guillochon, MM Kotze, K Maguire, MR Siebert, N Smith, J Strader, C Badenes, WE Kerzendorf, D Koester, M Kromer, B Miles, R Pakmor, J Schwab, O Toloza, S Toonen, DM Townsley, BJ Williams


Stellarator impurity flux driven by electric fields tangent to magnetic surfaces

NUCLEAR FUSION 58 (2018) ARTN 124005

I Calvo, FI Parra, J Luis Velaso, J Arturo Alonso, JM Garcia-Regana


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.


On the Kinematic Signature of the Galactic Warp As Revealed By the LAMOST-TGAS Data

ASTROPHYSICAL JOURNAL 864 (2018) ARTN 129

Y Huang, R Schonrich, X-W Liu, B-Q Chen, H-W Zhang, H-B Yuan, M-S Xiang, C Wang, Z-J Tian


Generation of Internal Waves by Buoyant Bubbles in Galaxy Clusters and Heating of Intracluster Medium

Monthly Notices of the Royal Astronomical Society Blackwell Publishing Inc. (2018)

C Zhang, E Churazov, AA Schekochihin

Buoyant bubbles of relativistic plasma in cluster cores plausibly play a key role in conveying the energy from a supermassive black hole to the intracluster medium (ICM) - the process known as radio-mode AGN feedback. Energy conservation guarantees that a bubble loses most of its energy to the ICM after crossing several pressure scale heights. However, actual processes responsible for transferring the energy to the ICM are still being debated. One attractive possibility is the excitation of internal waves, which are trapped in the cluster's core and eventually dissipate. Here we show that a sufficient condition for efficient excitation of these waves in stratified cluster atmospheres is flattening of the bubbles in the radial direction. In our numerical simulations, we model the bubbles phenomenologically as rigid bodies buoyantly rising in the stratified cluster atmosphere. We find that the terminal velocities of the flattened bubbles are small enough so that the Froude number ${\rm Fr}\lesssim 1$. The effects of stratification make the dominant contribution to the total drag force balancing the buoyancy force. In particular, clear signs of internal waves are seen in the simulations. These waves propagate horizontally and downwards from the rising bubble, spreading their energy over large volumes of the ICM. If our findings are scaled to the conditions of the Perseus cluster, the expected terminal velocity is $\sim100-200{\,\rm km\,s^{-1}}$ near the cluster cores, which is in broad agreement with direct measurements by the Hitomi satellite.

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