The global structure of magnetic fields and gas in simulated Milky Way-analogue galaxies

Abstract

We simulate an isolated, magnetised Milky Way-like disc galaxy using a self-consistent model of unresolved star formation and feedback, evolving the system until it reaches statistical steady state. We show that the quasi-steady-state structure is distinctly layered in galactocentric height $z$, with an innermost region having comparable gas and magnetic pressures (plasma beta $\beta \sim 1$), an outermost region having dominant gas pressures ($\beta \gg 1$), and an intermediate region between $300$ pc $\lesssim |z|\lesssim 3$ kpc that is dynamically dominated by magnetic fields ($\beta \ll 1$). We find field strengths, gas surface densities, and star formation rates that agree well with those observed both in the Galactic centre and in the Solar neighbourhood. The most significant dynamical effect of magnetic fields on the global properties of the disc is a reduction of the star formation rate by a factor of 1.5-2 with respect to an unmagnetised control simulation. At fixed star formation rate, there is no significant difference in the mass outflow rates or profiles between the magnetised and non-magnetised simulations. Our results for the global structure of the magnetic field have significant implications for models of cosmic ray-driven winds and cosmic-ray propagation in the Galaxy, and can be tested against observations with the forthcoming Square Kilometre Array and other facilities. Finally, we report the discovery of a physical error in the implementation of neutral gas heating and cooling in the popular GIZMO code, which may lead to qualitatively incorrect phase structures if not corrected.

12 pages + appendix, 7 figures. Simulated with 100 percent renewable electricity

References in corpus (19)

• Array Programming with NumPy
• COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies: I. Relations between H2, HI, stellar content and structural properties
• Radiative torques: Analytical Model and Basic Properties
• Momentum Injection by Supernovae in the Interstellar Medium
• Escape fraction of ionizing photons during reionization: effects due to supernova feedback and runaway OB stars
• Grackle: a Chemistry and Cooling Library for Astrophysics
• Planck intermediate results. XX. Comparison of polarized thermal emission from Galactic dust with simulations of MHD turbulence
• Characterizing mass, momentum, energy and metal outflow rates of multi-phase galactic winds in the FIRE-2 cosmological simulations
• Magnetohydrodynamic Simulations of Disk Galaxy Formation: the Magnetization of The Cold and Warm Medium
• The distribution of the ISM in the Milky Way A three-dimensional large-scale model
• Metal Cooling in Simulations of Cosmic Structure Formation
• First results from SMAUG: Characterization of Multiphase Galactic Outflows from a Suite of Local Star-Forming Galactic Disk Simulations
• SILCC VI -- Multi-phase ISM structure, stellar clustering, and outflows with supernovae, stellar winds, ionising radiation and cosmic rays
• Pressure balance in the multiphase ISM of cosmologically simulated disk galaxies
• The Fractional Ionization of the Warm Neutral Interstellar Medium
• The Physics of Galactic Winds Driven by Cosmic Rays I: Diffusion
• Momentum feedback from marginally-resolved HII regions in isolated disc galaxies
• Small-Scale Dynamo in Supernova-Driven Interstellar Turbulence
• Momentum Injection by Clustered Supernovae: Testing Subgrid Feedback Prescriptions

Cited by in corpus (18)

• Spirals in galaxies
• Photochemistry and Heating/Cooling of the Multiphase Interstellar Medium with UV Radiative Transfer for Magnetohydrodynamic Simulations
• Disk settling and dynamical heating: histories of Milky Way-mass stellar disks across cosmic time in the FIRE simulations
• The interplay between feedback, accretion, transport and winds in setting gas-phase metal distribution in galaxies
• Cosmic Ray Interstellar Propagation Tool using Itô Calculus (criptic): software for simultaneous calculation of cosmic ray transport and observational signatures
• The sub-critical illusion: synthetic Zeeman effect observations from galactic zoom-in simulations
• On the limitations of H alpha luminosity as a star formation tracer in spatially resolved observations
• The THESAN-ZOOM project: Star formation efficiency from giant molecular clouds to galactic scale in high-redshift starbursts
• The life cycle of giant molecular clouds in simulated Milky Way-mass galaxies
• CONGRuENTS (COsmic-ray, Neutrino, Gamma-ray and Radio Non-Thermal Spectra). I. A predictive model for galactic non-thermal emission
• Fundamental limits to orbit reconstruction due to non-conservation of stellar actions in a Milky Way-like simulation
• Reconciling the magnetic field in central disc galaxies with the dynamical mass using the cosmological simulations
• A path towards constraining the evolution of the interstellar medium and outflows in the Milky Way using APOGEE
• Wind of Change: Faraday Rotation in a Simulated Large Magellanic Cloud
• Anisotropic diffusion modeling of cosmic-ray lepton propagation
• Evolution of action-space coherence in a Milky Way-like simulation
• How non-thermal pressure impacts the modelling of star formation in galaxy formation simulations
• Magnetic fields in star forming environments: how does field strength affect gas on spiral arm and cloud scales?