1,275 research outputs found
Periodic motions galore: How to modify nonlinear evolution equations so that they feature a lot of periodic solutions
A simple trick is illustrated, whereby nonlinear evolution equations can be
modified so that they feature a lot - or, in some cases, only -- periodic
solutions. Several examples (ODEs and PDEs) are exhibited.Comment: arxiv version is already officia
Algebraically Linearizable Dynamical Systems
The main result of this paper is the evidence of an explicit linearization of
dynamical systems of Ruijsenaars-Schneider type and of the perturbations
introduced by F. Calogero of these systems with all orbits periodic of same
period. Several other systems share the existence of this explicit
linearization, among them, the Calogero-Moser system (with and without external
potential) and the Calogero-Sutherland system. This explicit linearization is
compared with the notion of maximal superintegrability which has been discussed
in several articles.Comment: 11 pages, Late
Lopsided Spiral Galaxies
The light distribution in the disks of many galaxies is non-axisymmetric or
`lopsided' with a spatial extent much larger along one half of a galaxy than
the other, as in M101. Recent near-IR observations show that lopsidedness is
common. The stellar disks in nearly 30 % of galaxies have significant
lopsidedness, greater than 10 % measured as the Fourier amplitude of the m=1
component normalized to the average value. This asymmetry is traced
particularly well by the atomic hydrogen gas distribution lying in the outer
parts. The lopsidedness also occurs in the nuclear regions, where the nucleus
is offset with respect to the outer isophotes. The galaxies in a group
environment show higher lopsidedness. The origin of lopsidedness could be due
to the disk response to a tidally distorted halo, or via gas accretion. The
lopsidedness has a large impact on the dynamics of the galaxy, its evolution,
the star formation in it, and on the growth of the central black hole and on
the nuclear fueling, merging of binary black holes etc. The disk lopsidedness
can be used as a diagnostic to study the halo asymmetry. This is an emerging
area in galactic structure and dynamics. In this review, the observations to
measure the lopsided distribution, as well as the theoretical progress made so
far to understand its origin and properties, and the related open problems will
be discussed. (abridged).Comment: 75 pages, 28 figures, a review article, to be published by Physics
Report
Near-IR photometry of disk galaxies: search for nuclear isophotal twist and double bars
We present a near-IR, mainly H band, photometry of 72 nearby disk galaxies.
The main goal of the survey was to search for isophotal twist inside their
nuclear regions. As the twist can be due in some cases to projection effects,
rather than resulting from a dynamical phenomenon, we deproject - under the
simplifying assumption of a 2D geometry - all galaxies whose disk position
angle and inclination are known, the latter not exceeding 75 degrees. We show
the ellipticity, position angle and surface brightness radial profiles, and
discuss how a projection of 2D and 3D bars can distort the isophotes, give an
illusion of a non-existing double bar or mask a real one. We report 15 new
double-barred galaxies and confirm 2 detected previously. We identify 14
additional twists not known before and we also find nuclear triaxial structures
in three SA galaxies. The frequency of Seyferts among galaxies with nuclear
bars or twists is high. As a secondary product, we publish structural
parameters (length and axis ratio) of large-scale bars in order to extend still
scarce data on bars in the near-IR.Comment: 11 pages of text (Astron. & Astroph. LaTeX l-aa macro) with 3
postscript figures, 7 additional pages of non-main-body postscript figures
containing contour and ellipse fitting plots of 72 galaxies; accepted by
Astronomy & Astrophysics Suppl. Se
Flat-Cored Dark Matter in Cuspy Clusters of Galaxies
Sand, Treu, & Ellis (2002) have measured the central density profile of
cluster MS2137-23 with gravitational lensing and velocity dispersion and
removed the stellar contribution with a reasonable M/L. The resulting dark
matter distribution within r<50 kpc was fitted by a density cusp of r^{-beta}
with beta=0.35. This stands in an apparent contradiction to the CDM prediction
of beta~1, and the disagreement worsens if adiabatic compression of the dark
matter by the infalling baryons is considered. Following El-Zant, Shlosman &
Hoffman (2001), we argue that dynamical friction acting on galaxies moving
within the dark matter background counters the effect of adiabatic compression
by transfering the orbital energy of galaxies to the dark matter, thus heating
up and softening the central density cusp. Using N-body simulations of massive
solid clumps moving in clusters we show that indeed the inner dark matter
distribution flattens (with beta approx 0.35 for a cluster like MS2137-23) when
the galaxies spiral inward. We find as a robust result that while the dark
matter distribution becomes core-like, the overall mass distribution preserves
its cuspy nature, in agreement with X-ray and lensing observations of clusters.Comment: 7 pages, 3 figures, to be published in Astrophysical Journal Letter
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