Small-Scale Dynamo in Supernova-Driven Interstellar Turbulence. (arXiv:2010.01833v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Gent_F/0/1/0/all/0/1">Frederick A. Gent</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Low_M/0/1/0/all/0/1">Mordecai-Mark Mac Low</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kapyla_M/0/1/0/all/0/1">Maarit J. Kapyla</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Singh_N/0/1/0/all/0/1">Nishant K. Singh</a>
Magnetic fields grow quickly even at early cosmological times, suggesting the
action of a small-scale dynamo (SSD) in the interstellar medium of galaxies.
Many studies have focused on idealized turbulent driving of the SSD. Here we
simulate more realistic supernova-driven turbulence to determine whether it can
drive an SSD. Magnetic field growth occurring in our models appears consistent
with SSD action, and inconsistent with simple tangling of magnetic fields. We
vary the physical resistivity, $eta$, as well as the numerical resolution and
supernova rate, $dotsigma$, to delineate the regime in which an SSD occurs.
For a given $dotsigma$ we find convergence for SSD growth rate with
resolution of a parsec. For $dotsigmasimeqdotsigma_{rm sn}$, with
$dotsigma_{rm sn}$ the solar neighbourhood rate, the critical resistivity
below which an SSD occurs is $0.005>eta_{rm crit}>0.001{,rm kpc}^{-1}{,rm
km~ s}^{-1}$, and this increases with the supernova rate. Across the modelled
range of 0.5 to 4~pc resolution we find that for $eta<eta_{rm crit}$, the
SSD saturates at about 5% of kinetic energy equipartion, independent of growth
rate. In the range $0.2dotsigma_{rm sn}leq dotsigmaleq8dotsigma_{rm
sn}$ growth rate increases with $dotsigma$, despite the negative impact
expected from increased Mach numbers. SSDs in the supernova-driven interstellar
medium commonly exhibit erratic growth.
Magnetic fields grow quickly even at early cosmological times, suggesting the
action of a small-scale dynamo (SSD) in the interstellar medium of galaxies.
Many studies have focused on idealized turbulent driving of the SSD. Here we
simulate more realistic supernova-driven turbulence to determine whether it can
drive an SSD. Magnetic field growth occurring in our models appears consistent
with SSD action, and inconsistent with simple tangling of magnetic fields. We
vary the physical resistivity, $eta$, as well as the numerical resolution and
supernova rate, $dotsigma$, to delineate the regime in which an SSD occurs.
For a given $dotsigma$ we find convergence for SSD growth rate with
resolution of a parsec. For $dotsigmasimeqdotsigma_{rm sn}$, with
$dotsigma_{rm sn}$ the solar neighbourhood rate, the critical resistivity
below which an SSD occurs is $0.005>eta_{rm crit}>0.001{,rm kpc}^{-1}{,rm
km~ s}^{-1}$, and this increases with the supernova rate. Across the modelled
range of 0.5 to 4~pc resolution we find that for $eta<eta_{rm crit}$, the
SSD saturates at about 5% of kinetic energy equipartion, independent of growth
rate. In the range $0.2dotsigma_{rm sn}leq dotsigmaleq8dotsigma_{rm
sn}$ growth rate increases with $dotsigma$, despite the negative impact
expected from increased Mach numbers. SSDs in the supernova-driven interstellar
medium commonly exhibit erratic growth.
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