1,439 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
Forming disk galaxies in wet major mergers. I. Three fiducial examples
Using three fiducial Nbody+SPH simulations, we follow the merging of two disk
galaxies with a hot gaseous halo component each, and examine whether the merger
remnant can be a spiral galaxy. The stellar progenitor disks are destroyed by
violent relaxation during the merging and most of their stars form a classical
bulge, while the remaining form a thick disk and its bar. A new stellar disk
forms subsequently and gradually in the remnant from the gas accreted mainly
from the halo. It is vertically thin and well extended in its equatorial plane.
A bar starts forming before the disk is fully in place, contrary to what is
assumed in idealised simulations of isolated bar-forming galaxies. It has
morphological features such as ansae and boxy/peanut bulges. Stars of different
ages populate different parts of the box/peanut. A disky pseudobulge forms
also, so that by the end of the simulation, all three types of bulges coexist.
The oldest stars are found in the classical bulge, followed by those of the
thick disk, then by those in the thin disk. The youngest stars are in the
spiral arms and the disky pseudobulge. The disk surface density profiles are of
type II (exponential with downbending), and the circular velocity curves are
flat and show that the disks are submaximum in these examples: two clearly so
and one near-borderline between maximum and submaximum. On average, only
roughly between 10 and 20% of the stellar mass is in the classical bulge of the
final models, i.e. much less than in previous simulations.Comment: 17 pages, 8 figures, accepted for publication in ApJ. V2: replaced
Figure 4 with correct versio
Towards a Maximal Mass Model
We investigate the possibility to construct a generalization of the Standard
Model, which we call the Maximal Mass Model because it contains a limiting mass
for its fundamental constituents. The parameter is considered as a new
universal physical constant of Nature and therefore is called the fundamental
mass. It is introduced in a purely geometrical way, like the velocity of light
as a maximal velocity in the special relativity. If one chooses the Euclidean
formulation of quantum field theory, the adequate realization of the limiting
mass hypothesis is reduced to the choice of the de Sitter geometry as the
geometry of the 4-momentum space. All fields, defined in de Sitter p-space in
configurational space obey five dimensional Klein-Gordon type equation with
fundamental mass as a mass parameter. The role of dynamical field variables
is played by the Cauchy initial conditions given at , guarantying the
locality and gauge invariance principles. The corresponding to the geometrical
requirements formulation of the theory of scalar, vector and spinor fields is
considered in some detail. On a simple example it is demonstrated that the
spontaneously symmetry breaking mechanism leads to renormalization of the
fundamental mass . A new geometrical concept of the chirality of the fermion
fields is introduced. It would be responsible for new measurable effects at
high energies . Interaction terms of a new type, due to the existence
of the Higgs boson are revealed. The most intriguing prediction of the new
approach is the possible existence of exotic fermions with no analogues in the
SM, which may be candidate for dark matter constituents.Comment: 28 page
Superhyperfine interactions in Ce3+ doped LiYF4 crystal: ENDOR measurements
The first observation of the resolved Mims electron-nuclear double resonance
(ENDOR) spectra from the nearby and remote nuclei of 19F and 7Li nuclei on
impurity Ce3+ ions in LiYF4 crystal is reported. It shows that LiYF4:Ce3+
system can be exploited as a convenient matrix for performing spin
manipulations and adjusting quantum computation protocols while ENDOR technique
could be used for the investigation of electron-nuclear interaction with all
the nuclei of the system and exploited for the electron-nuclear spin
manipulations.Comment: 4 pages, 2 figures, 1 Table. Reported on Theor-2017 (Kazan, Russia)
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