2,881 research outputs found
Bending instability in galactic discs. Advocacy of the linear theory
We demonstrate that in N-body simulations of isolated disc galaxies there is
numerical vertical heating which slowly increases the vertical velocity
dispersion and the disc thickness. Even for models with over a million
particles in a disc, this heating can be significant. Such an effect is just
the same as in numerical experiments by Sellwood (2013). We also show that in a
stellar disc, outside a boxy/peanut bulge, if it presents, the saturation level
of the bending instability is rather close to the value predicted by the linear
theory. We pay attention to the fact that the bending instability develops and
decays very fast, so it couldn't play any role in secular vertical heating.
However the bending instability defines the minimal value of the ratio between
the vertical and radial velocity dispersions
(so indirectly the minimal thickness) which could have stellar discs in real
galaxies. We demonstrate that observations confirm last statement.Comment: 8 pages, 8 figures, accepted for publication in MNRA
Metallicity-dependendent kinematics and morphology of the Milky Way bulge
We use N-body chemo-dynamic simulations to study the coupling between
morphology, kinematics and metallicity of the bar/bulge region of our Galaxy.
We make qualitative comparisons of our results with available observations and
find very good agreement. We conclude that this region is complex, since it
comprises several stellar components with different properties -- i.e. a
boxy/peanut bulge, thin and thick disc components, and, to lesser extents, a
disky pseudobulge, a stellar halo and a small classical bulge -- all cohabiting
in dynamical equilibrium. Our models show strong links between kinematics and
metallicity, or morphology and metallicity, as already suggested by a number of
recent observations. We discuss and explain these links.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Forming disc galaxies in major mergers: III. The effect of angular momentum on the radial density profiles of disc galaxies
We study the effect of angular momentum on the surface density profiles of
disc galaxies, using high resolution simulations of major mergers whose
remnants have downbending radial density profiles (type II). As described in
the previous papers of this series, in this scenario, most of the disc mass is
acquired after the collision via accretion from a hot gaseous halo. We find
that the inner and outer disc scalelengths, as well as the break radius,
correlate with the total angular momentum of the initial merging system, and
are larger for high angular momentum systems. We follow the angular momentum
redistribution in our simulated galaxies, and find that, like the mass, the
disc angular momentum is acquired via accretion, i.e. to the detriment of the
gaseous halo. Furthermore, high angular momentum systems give more angular
momentum to their discs, which affects directly their radial density profile.
Adding simulations of isolated galaxies to our sample, we find that the
correlations are valid also for disc galaxies evolved in isolation. We show
that the outer part of the disc at the end of the simulation is populated
mainly by inside-out stellar migration, and that in galaxies with higher
angular momentum, stars travel radially further out. This, however, does not
mean that outer disc stars (in type II discs) were mostly born in the inner
disc. Indeed, generally the break radius increases over time, and not taking
this into account leads to overestimating the number of stars born in the inner
disc.Comment: 12 pages, 13 figures, accepted for publication in MNRA
On Influence of Intensive Stationary Electromagnetic Field on the Behavior of Fermionic Systems
Exact solutions of Schroedinger and Pauli equations for charged particles in
an external stationary electromagnetic field of an arbitrary configuration are
constructed. Green functions of scalar and spinor particles are calculated in
this field. The corresponding equations for complex energy of particles bounded
by short range potential are deduced. Boundary condition typical for delta -
potential is not used in the treatment. Explicit analytical expressions are
given for the shift and width of a quasistationary level for different
configurations of the external field. The critical value of electric field in
which the idea of quasistationary level becomes meaningless is calculated. It
is shown that the common view on the stabilizing role of magnetic field
concerns only scalar particles.Comment: 15 pages, no figures, LaTeX2
Bar formation and evolution in disc galaxies with gas and a triaxial halo: Morphology, bar strength and halo properties
We follow the formation and evolution of bars in N-body simulations of disc
galaxies with gas and/or a triaxial halo. We find that both the relative gas
fraction and the halo shape play a major role in the formation and evolution of
the bar. In gas-rich simulations, the disc stays near-axisymmetric much longer
than in gas-poor ones, and, when the bar starts growing, it does so at a much
slower rate. Due to these two effects combined, large-scale bars form much
later in gas-rich than in gas-poor discs. This can explain the observation that
bars are in place earlier in massive red disc galaxies than in blue spirals. We
also find that the morphological characteristics in the bar region are strongly
influenced by the gas fraction. In particular, the bar at the end of the
simulation is much weaker in gas-rich cases. In no case did we witness bar
destruction.
Halo triaxiality has a dual influence on bar strength. In the very early
stages of the simulation it induces bar formation to start earlier. On the
other hand, during the later, secular evolution phase, triaxial haloes lead to
considerably less increase of the bar strength than spherical ones. The shape
of the halo evolves considerably with time. The inner halo parts may become
more elongated, or more spherical, depending on the bar strength. The main body
of initially triaxial haloes evolves towards sphericity, but in initially
strongly triaxial cases it stops well short of becoming spherical. Part of the
angular momentum absorbed by the halo generates considerable rotation of the
halo particles that stay located relatively near the disc for long periods of
time. Another part generates halo bulk rotation, which, contrary to that of the
bar, increases with time but stays small.Comment: 21 pages, 16 figures, accepted for publication in MNRAS. A high
resolution version is at
http://195.221.212.246:4780/dynam/paper/amr12/rm_3axhalo_gas.pd
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