Browsing by Author "Fletcher, A."
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- The distribution of mean and fluctuating magnetic fields in the multiphase interstellar medium
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-01-01) Evirgen, C.~C.; Gent, F.~A.; Shukurov, A.; Fletcher, A.; Bushby, P.We explore the effects of the multiphase structure of the interstellar medium (ISM) on galactic magnetic fields. Basing our analysis on compressible magnetohydrodynamic simulations of supernova-driven turbulence in the ISM, we investigate the properties of both the mean and fluctuating components of the magnetic field. We find that the mean magnetic field preferentially resides in the warm phase and is generally absent from the hot phase. The fluctuating magnetic field does not show such pronounced sensitivity to the multiphase structure. - The supernova-regulated ISM - VI. Magnetic effects on the structure of the interstellar medium
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-10) Evirgen, C. C.; Gent, F. A.; Shukurov, A.; Fletcher, A.; Bushby, P. J.We explore the effect of magnetic fields on the vertical distribution and multiphase structure of the supernova-driven interstellar medium in simulations that admit dynamo action. As the magnetic field is amplified to become dynamically significant, gas becomes cooler and its distribution in the disc becomes more homogeneous. We attribute this to magnetic quenching of vertical velocity, which leads to a decrease in the cooling length of hot gas. A non-monotonic vertical distribution of the large-scale magnetic field strength, with the maximum at |z| approximate to 300pc causes a downward pressure gradient below the maximum which acts against outflow driven by SN explosions, while it provides pressure support above the maximum. - The supernova-regulated ISM - VI. Magnetic effects on the structure of the interstellar medium
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-10) Evirgen, C. C.; Gent, F. A.; Shukurov, A.; Fletcher, A.; Bushby, P. J.We explore the effect of magnetic fields on the vertical distribution and multiphase structure of the supernova-driven interstellar medium in simulations that admit dynamo action. As the magnetic field is amplified to become dynamically significant, gas becomes cooler and its distribution in the disc becomes more homogeneous. We attribute this to magnetic quenching of vertical velocity, which leads to a decrease in the cooling length of hot gas. A non-monotonic vertical distribution of the large-scale magnetic field strength, with the maximum at |z| approximate to 300pc causes a downward pressure gradient below the maximum which acts against outflow driven by SN explosions, while it provides pressure support above the maximum. - Supernova-regulated ISM. V. Space and Time Correlations
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-11-20) Hollins, J. F.; Sarson, G. R.; Shukurov, A.; Fletcher, A.; Gent, F. A.We apply correlation analysis to random fields in numerical simulations of the supernova-driven interstellar medium (ISM) with the magnetic field produced by dynamo action. We solve the magnetohydrodynamic (MHD) equations in a shearing Cartesian box representing a local region of the ISM, subject to thermal and kinetic energy injection by supernova explosions, and parameterized, optically thin radiative cooling. We consider the cold, warm, and hot phases of the ISM separately; the analysis mostly considers the warm gas, which occupies the bulk of the domain. Various physical variables have different correlation lengths in the warm phase: 40, 50, and 60 pc for the random magnetic field, density, and velocity, respectively, in the midplane. The correlation time of the random velocity is comparable to the eddy turnover time, about 107 year, although it may be shorter in regions with a higher star formation rate. The random magnetic field is anisotropic, with the standard deviations of its components bx by bz having approximate ratios 0.5 0.6 0.6 in the midplane. The anisotropy is attributed to the global velocity shear from galactic differential rotation and locally inhomogeneous outflow to the galactic halo. The correlation length of Faraday depth along the z axis, 120 pc, is greater than for electron density, 60-90 pc, and the vertical magnetic field, 60 pc. Such comparisons may be sensitive to the orientation of the line of sight. Uncertainties of the structure functions of synchrotron intensity rapidly increase with the scale. This feature is hidden in a power spectrum analysis, which can undermine the usefulness of power spectra for detailed studies of interstellar turbulence.