1,988 research outputs found
A numerical study of interactions and stellar bars
For several decades it has been known that stellar bars in disc galaxies can
be triggered by interactions, or by internal processes such as dynamical
instabilities. In this work, we explore the differences between these two
mechanisms using numerical simulations. We perform two groups of simulations
based on isolated galaxies, one group in which a bar develops naturally, and
another group in which the bar could not develop in isolation. The rest of the
simulations recreate 1:1 coplanar fly-by interactions computed with the impulse
approximation. The orbits we use for the interactions represent the fly-bys in
groups or clusters of different masses accordingly to the velocity of the
encounter. In the analysis we focus on bars' amplitude, size, pattern speed and
their rotation parameter, . The latter is used to
define fast (). Compared with
equivalent isolated galaxies we find that bars affected or triggered by
interactions: (i) remain in the slow regime for longer; (ii) are more boxy in
face-on views; (iii) they host kinematically hotter discs. Within this set of
simulations we do not see strong differences between retrograde or prograde
fly-bys. We also show that slow interactions can trigger bar formation.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
Confined photon modes with triangular symmetry in hexagonal microcavities in 2D photonic Crystals
We present theoretical and experimental studies of the size and thickness
dependencies of the optical emission spectra from microcavities with hexagonal
shape in films of two-dimensional photonic crystal. A semiclassical plane-wave
model, which takes into account the electrodynamic properties of quasi-2D
planar photonic microcavity, is developed to predict the eigenfrequencies of
the confined photon modes as a function of both the hexagon-cavity size and the
film thickness. Modes with two different symmetries, triangular and hexagonal,
are critically analyzed. It is shown that the model of confined photon modes
with triangular symmetry gives a better agreement between the predicted
eigenmodes and the observed resonances.Comment: 14 pages, 6 figure
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