470 research outputs found
First direct identification of the barlens vertical structure in galaxy models
Applying spectral dynamics methods to one typical -body model with a
barlens, we dissect the modelled bar into separate components supported by
completely different types of orbits. We identify at least four components: a
narrow elongated bar, a boxy bar, and two components contributing to the
barlens. We analyse the vertical structure of all components that make up the
thick part of the bar, which has a boxy/peanut shape (B/P bulge). We show that
the `peanut' shape is mainly due to the orbits that assemble the boxy part of
the face-on bar. We associate the X-shape with the narrow and elongated bar.
The wider part of the barlens with square-like isophotes contributes to the
boxy shape of the B/P bulge when we observe the galaxy edge-on. However, the
part of the barlens with rounded isophotes in the face-on view is a rather flat
structure in the vertical direction without any significant off-centre
protrusions. Thus, for the first time, we demonstrate that the rounded face-on
barlens cannot be entirely associated with the B/P bulge.Comment: 5 pages, 5 figures, accepted to Astronomy and Astrophysics on March
26, 202
B/PS bulges and barlenses from a kinematic viewpoint. I
A significant part of barred disc galaxies exhibits boxy/peanut-shaped
structures (B/PS bulges) at high inclinations. Another structure also
associated with the bar is a barlens, often observed in galaxies in a position
close to face-on. At this viewing angle, special kinematic tests are required
to detect a 3D extension of the bars in the vertical direction (B/PS bulges).
We use four pure -body models of galaxies with B/PS bulges, which have
different bar morphology from bars with barlenses to the so-called face-on
peanut bars. We analyse the kinematics of our models to establish how the
structural features of B/PS bulges manifest themselves in the kinematics for
galaxies at intermediate inclinations and whether these features are related to
the barlenses. We apply the dissection of the bar into different orbital groups
to determine which of them are responsible for the features of the LOSVD
(line-of-sight velocity distribution), i.e., for the deep minima of the
parameter along the major axis of the bar. As a result, we claim that for our
models at the face-on position, the kinematic signatures of a `peanut' indeed
track the vertical density distribution features. We conclude that orbits
responsible for such kinematic signatures differ from model to model. We pay
special attention to the barlens model. We show that orbits assembled into
barlens are not responsible for the kinematic signatures of B/PS bulges. The
results presented in this work are applicable to the interpretation of IFU
observations of real galaxies.Comment: 18 page
Dirac fermions in a power-law-correlated random vector potential
We study localization properties of two-dimensional Dirac fermions subject to
a power-law-correlated random vector potential describing, e.g., the effect of
"ripples" in graphene. By using a variety of techniques (low-order perturbation
theory, self-consistent Born approximation, replicas, and supersymmetry) we
make a case for a possible complete localization of all the electronic states
and compute the density of states.Comment: Latex, 4+ page
Vector solitons in (2+1) dimensions
We address the problem of existence and stability of vector spatial solitons
formed by two incoherently interacting optical beams in bulk Kerr and saturable
media. We identify families of (2+1)-dimensional two-mode self-trapped beams,
with and without a topological charge, and describe their properties
analytically and numerically.Comment: 3 pages, 5 figures, submitted to Opt. Let
Observation of dipole-mode vector solitons
We report on the first experimental observation of a novel type of optical
vector soliton, a {\em dipole-mode soliton}, recently predicted theoretically.
We show that these vector solitons can be generated in a photorefractive medium
employing two different processes: a phase imprinting, and a symmetry-breaking
instability of a vortex-mode vector soliton. The experimental results display
remarkable agreement with the theory, and confirm the robust nature of these
radially asymmetric two-component solitary waves.Comment: 4 pages, 8 figures; pictures in the PRL version are better qualit
Observation of discrete vortex solitons in optically-induced photonic lattices
We report on the frst experimental observation of discrete vortex solitons in
two-dimensional optically-induced photonic lattices. We demonstrate strong
stabilization of an optical vortex by the lattice in a self-focusing nonlinear
medium and study the generation of the discrete vortices from a broad class of
singular beams.Comment: 4pages, 5 colour figures. to appear in PR
Stable ring vortex solitons in Bessel optical lattices
Stable ring vortex solitons, featuring a bright-shape, appear to be very rare
in nature. However, here we show that they exist and can be made dynamically
stable in defocusing cubic nonlinear media with an imprinted Bessel optical
lattice. We find the families of vortex lattice solitons and reveal their
salient properties, including the conditions required for their stability. We
show that the higher the soliton topological charge, the deeper the lattice
modulation necessary for stabilization.Comment: 14 pages, 4 figures, submitted to Physical Review Letter
Svortices and the fundamental modes of the "snake instability": Possibility of observation in the gaseous Bose-Einstein Condensate
The connection between quantized vortices and dark solitons in a long and
thin, waveguide-like trap geometry is explored in the framework of the
non-linear Schr\"odinger equation. Variation of the transverse confinement
leads from the quasi-1D regime where solitons are stable to 2D (or 3D)
confinement where soliton stripes are subject to a transverse modulational
instability known as the ``snake instability''. We present numerical evidence
of a regime of intermediate confinement where solitons decay into single,
deformed vortices with solitonic properties, also called svortices, rather than
vortex pairs as associated with the ``snake'' metaphor. Further relaxing the
transverse confinement leads to production of 2 and then 3 vortices, which
correlates perfectly with a Bogoliubov-de Gennes stability analysis. The decay
of a stationary dark soliton (or, planar node) into a single svortex is
predicted to be experimentally observable in a 3D harmonically confined dilute
gas Bose-Einstein condensate.Comment: 4 pages, 4 figure
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