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Theoretical physicists working at a blackboard collaboration pod in the Beecroft building.
Credit: Jack Hobhouse

John Magorrian

Associate Professor of Theoretical Astrophysics

Research theme

  • Astronomy and astrophysics

Sub department

  • Rudolf Peierls Centre for Theoretical Physics

Research groups

  • Galaxy formation and evolution
  • Theoretical astrophysics and plasma physics at RPC
John.Magorrian@physics.ox.ac.uk
  • About
  • Publications

Mapping dust in the giant molecular cloud Orion A

Monthly Notices of the Royal Astronomical Society Oxford University Press 528:4 (2024) 5763-5782

Authors:

Amery Gration, Stephen Magorrian

Abstract:

The Sun is located close to the Galactic mid-plane, meaning that we observe the Galaxy through significant quantities of dust. Moreover, the vast majority of the Galaxy’s stars also lie in the disc, meaning that dust has an enormous impact on the massive astrometric, photometric and spectroscopic surveys of the Galaxy that are currently underway. To exploit the data from these surveys we require good three-dimensional maps of the Galaxy’s dust. We present a new method for making such maps in which we form the best linear unbiased predictor of the extinction at an arbitrary point based on the extinctions for a set of observed stars. This method allows us to avoid the artificial inhomogeneities (so-called ‘fingers of God’) and resolution limits that are characteristic of many published dust maps. Moreover, it requires minimal assumptions about the statistical properties of the interstellar medium. In fact, we require only a model of the first and second moments of the dust density field. The method is suitable for use with directly measured extinctions, such as those provided by the Rayleigh–Jeans colour excess method, and inferred extinctions, such as those provided by hierarchical Bayesian models like StarHorse. We test our method by mapping dust in the region of the giant molecular cloud Orion A. Our results indicate a foreground dust cloud at a distance of 350 pc, which has been identified in work by another author.
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Mapping dust in the giant molecular cloud Orion A

(2024)

Authors:

Amery Gration, John Magorrian
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On the self-consistent time-dependent linearized response of stellar discs to external perturbations

(2022)

Authors:

Dominic Dootson, John Magorrian
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Self-consistent modelling of the Milky Way’s nuclear stellar disc

Monthly Notices of the Royal Astronomical Society Oxford University Press 512:2 (2022) 1857-1884

Authors:

Mattia C Sormani, Jason L Sanders, Tobias K Fritz, Leigh C Smith, Ortwin Gerhard, Rainer Schödel, Stephen Magorrian, Nadine Neumayer, Francisco Nogueras-Lara, Anja Feldmeier-Krause, Alessandra Mastrobuono-Battisti, Mathias Schultheis, Banafsheh Shahzamanian, Eugene Vasiliev, Ralf S Klessen, Philip Lucas, Dante Minniti

Abstract:

The nuclear stellar disc (NSD) is a flattened high-density stellar structure that dominates the gravitational field of the Milky Way at Galactocentric radius $30\, {\rm pc}\lesssim R\lesssim 300\, {\rm pc}$. We construct axisymmetric self-consistent equilibrium dynamical models of the NSD in which the distribution function is an analytic function of the action variables. We fit the models to the normalized kinematic distributions (line-of-sight velocities + VIRAC2 proper motions) of stars in the NSD survey of Fritz et al., taking the foreground contamination due to the Galactic Bar explicitly into account using an N-body model. The posterior marginalized probability distributions give a total mass of $M_{\rm NSD} = 10.5^{+1.1}_{-1.0} \times 10^8 \, \, \rm M_\odot$, roughly exponential radial and vertical scale lengths of $R_{\rm disc} = 88.6^{+9.2}_{-6.9} \, {\rm pc}$ and $H_{\rm disc}=28.4^{+5.5}_{-5.5} \, {\rm pc}$, respectively, and a velocity dispersion $\sigma \simeq 70\, {\rm km\, s^{-1}}$ that decreases with radius. We find that the assumption that the NSD is axisymmetric provides a good representation of the data. We quantify contamination from the Galactic Bar in the sample, which is substantial in most observed fields. Our models provide the full 6D (position + velocity) distribution function of the NSD, which can be used to generate predictions for future surveys. We make the models publicly available as part of the software package agama.
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Self-consistent modelling of the Milky Way's Nuclear Stellar Disc

(2021)

Authors:

Mattia C Sormani, Jason L Sanders, Tobias K Fritz, Leigh C Smith, Ortwin Gerhard, Rainer Schoedel, John Magorrian, Nadine Neumayer, Francisco Nogueras-Lara, Anja Feldmeier-Krause, Alessandra Mastrobuono-Battisti, Mathias Schultheis, Banafsheh Shahzamanian, Eugene Vasiliev, Ralf S Klessen, Philip Lucas, Dante Minniti
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