Inverse energy cascade in self-gravitating collisionless dark matter flow and effects of halo shape. (arXiv:2110.13885v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Zhijie/0/1/0/all/0/1">Zhijie</a> (Jay)Xu
Halo-mediated mass and energy cascades are key to understand dark matter
flow. Both cascades origin from the mass exchange between halo and out-of-halo
sub-systems. Kinetic energy can be from the motion of halos and particle motion
in halos. Similarly, potential energy can be due to the inter- and intra-halo
interactions. Intra-halo virial equilibrium is established much faster than
inter-halo. Change of energy of entire system comes from virilization in halos.
At statistically steady state, continuous mass exchange is required to sustain
growth of total halo mass $M_hpropto a^{1/2}$ and energy $Epropto a^{3/2}$,
where $a$ is scale factor. Inverse cascade is identified for kinetic energy
that is transferred from the smallest scale to large mass scales. This is
sustained by the direct cascade of potential energy from large to small scale.
Both energies have a scale- and time-independent flux in propagation range that
is proportional to mass flux. Energy cascade is mostly facilitated by mass
cascade, which can be quantitatively described by mass accretion of typical
halos. Halo radial, angular momentum, and angular velocity are modelled and
inverse cascade is identified for the coherent radial and rotational motion in
halos. In turbulence, vortex stretching (shape changing) along its axis of spin
enables energy cascade from large to small length scales. However, change in
halo shape is not the dominant mechanism for energy cascade as the moment of
inertial gained from shape changing is less than 2 times. Large halos exhibit
preference for prolateness over oblateness and most halos have spin axis
perpendicular to major axis. Since mass cascade is local in mass space, halo
shape evolves continuously in mass space with halos formed by incrementally
inheriting structure from progenitor halos. A unique evolution path of halos is
found that gradually approaches sphere with increasing size.
Halo-mediated mass and energy cascades are key to understand dark matter
flow. Both cascades origin from the mass exchange between halo and out-of-halo
sub-systems. Kinetic energy can be from the motion of halos and particle motion
in halos. Similarly, potential energy can be due to the inter- and intra-halo
interactions. Intra-halo virial equilibrium is established much faster than
inter-halo. Change of energy of entire system comes from virilization in halos.
At statistically steady state, continuous mass exchange is required to sustain
growth of total halo mass $M_hpropto a^{1/2}$ and energy $Epropto a^{3/2}$,
where $a$ is scale factor. Inverse cascade is identified for kinetic energy
that is transferred from the smallest scale to large mass scales. This is
sustained by the direct cascade of potential energy from large to small scale.
Both energies have a scale- and time-independent flux in propagation range that
is proportional to mass flux. Energy cascade is mostly facilitated by mass
cascade, which can be quantitatively described by mass accretion of typical
halos. Halo radial, angular momentum, and angular velocity are modelled and
inverse cascade is identified for the coherent radial and rotational motion in
halos. In turbulence, vortex stretching (shape changing) along its axis of spin
enables energy cascade from large to small length scales. However, change in
halo shape is not the dominant mechanism for energy cascade as the moment of
inertial gained from shape changing is less than 2 times. Large halos exhibit
preference for prolateness over oblateness and most halos have spin axis
perpendicular to major axis. Since mass cascade is local in mass space, halo
shape evolves continuously in mass space with halos formed by incrementally
inheriting structure from progenitor halos. A unique evolution path of halos is
found that gradually approaches sphere with increasing size.
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