7,050 research outputs found
Bounds for axially symmetric linear perturbations for the extreme Kerr black hole
We obtain remarkably simple integral bounds for axially symmetric linear
perturbations for the extreme Kerr black hole in terms of conserved energies.
From these estimates we deduce pointwise bounds for the perturbations outside
the horizon.Comment: 15 page
Construction of the Lyapunov spectrum in a chaotic system displaying phase synchronization
We consider a three-dimensional chaotic system consisting of the suspension
of Arnold's cat map coupled with a clock via a weak dissipative interaction. We
show that the coupled system displays a synchronization phenomenon, in the
sense that the relative phase between the suspension flow and the clock locks
to a special value, thus making the motion fall onto a lower dimensional
attractor. More specifically, we construct the attractive invariant manifold,
of dimension smaller than three, using a convergent perturbative expansion.
Moreover, we compute via convergent series the Lyapunov exponents, including
notably the central one. The result generalizes a previous construction of the
attractive invariant manifold in a similar but simpler model. The main novelty
of the current construction relies in the computation of the Lyapunov spectrum,
which consists of non-trivial analytic exponents. Some conjectures about a
possible smoothening transition of the attractor as the coupling is increased
are also discussed.Comment: 24 pages, 10 figure
Mass models from high-resolution HI data of the dwarf galaxy NGC 1560
We present HI observations performed at the GMRT of the nearby dwarf galaxy
NGC 1560. This Sd galaxy is well-known for a distinct "wiggle" in its rotation
curve. Our new observations have twice the resolution of the previously
published HI data. We derived the rotation curve by taking projection effects
into account, and we verified the derived kinematics by creating model
datacubes. This new rotation curve is similar to the previously published one:
we confirm the presence of a clear wiggle. The main differences are in the
innermost ~100 arcsec of the rotation curve, where we find slightly (<~ 5 km/s)
higher velocities. Mass modelling of the rotation curve results in good fits
using the core-dominated Burkert halo (which however does not reproduce the
wiggle), bad fits using the a Navarro, Frenk & White halo, and good fits using
MOND (Modified Newtonian Dynamics), which also reproduces the wiggle.Comment: Accepted for publication in MNRAS. 11 pages, 13 figures.
High-resolution version available at
http://users.ugent.be/~ggianfra/1560_final.pd
Supernova neutrino physics with a nuclear emulsion detector
The existence of the coherent neutrino-nucleus scattering reaction requires
to evaluate, for any detector devoted to WIMP searches, the irreducible
background due to conventional neutrino sources and at same time, it gives a
unique chance to reveal supernova neutrinos. We report here a detailed study
concerning a new directional detector, based on the nuclear emulsion
technology. A Likelihood Ratio test shows that, in the first years of
operations and with a detector mass of several tens of tons, the observation of
the supernova signal can be achieved. The determination of the distance of the
supernova from the neutrinos and the observation of B neutrinos are also
discussed.Comment: 22 pages, 12 figure
Remarks on the properties of elliptical galaxies in modified Newtonian dynamics
Two incorrect arguments against MOND in elliptical galaxies could be that the
equivalent circular velocity curves tend to become flat at much larger
accelerations than in spiral galaxies, and that the Newtonian dark matter halos
are more concentrated than in spirals. Here, we compare published scaling
relations for the dark halos of elliptical galaxies to the scaling relations
expected for MONDian phantom halos. We represent the baryonic content of
galaxies by spherical profiles, and their corresponding MONDian phantom halos
by logarithmic halos. We then derive the surface densities, central densities,
and phase space densities and compare them with published scaling relations. We
conclude that it is possible to get flat circular velocity curves at high
acceleration in MOND, and that this happens for baryonic distributions
described by Jaffe profiles in the region where the circular velocity curve is
flat. Moreover, the scaling relations of dark halos of ellipticals are
remarkably similar to the scaling relations of phantom halos of MOND.Comment: Accepted for publication in A and
Isolated and non-isolated dwarfs in terms of modified Newtonian dynamics
Within the framework of modified Newtonian dynamics (MOND) we investigate the
kinematics of two dwarf spiral galaxies belonging to very different
environments, namely KK 246 in the Local Void and Holmberg II in the M81 group.
A mass model of the rotation curve of KK 246 is presented for the first time,
and we show that its observed kinematics are consistent with MOND. We re-derive
the outer rotation curve of Holmberg II, by modelling its HI data cube, and
find that its inclination should be closer to face-on than previously derived.
This implies that Holmberg II has a higher rotation velocity in its outer
parts, which, although not very precisely constrained, is consistent with the
MOND prediction.Comment: Accepted in A&A as a Research Note. 6 pages, 3 figure
The distribution of interstellar dust in CALIFA edge-on galaxies via oligochromatic radiative transfer fitting
We investigate the amount and spatial distribution of interstellar dust in
edge-on spiral galaxies, using detailed radiative transfer modeling of a
homogeneous sample of 12 galaxies selected from the CALIFA survey. Our
automated fitting routine, FitSKIRT, was first validated against artificial
data. This is done by simultaneously reproducing the SDSS -, -, - and
-band observations of a toy model in order to combine the information
present in the different bands. We show that this combined, oligochromatic
fitting, has clear advantages over standard monochromatic fitting especially
regarding constraints on the dust properties. We model all galaxies in our
sample using a three-component model, consisting of a double exponential disc
to describe the stellar and dust discs and using a S\'ersic profile to describe
the central bulge. The full model contains 19 free parameters, and we are able
to constrain all these parameters to a satisfactory level of accuracy without
human intervention or strong boundary conditions. Apart from two galaxies, the
entire sample can be accurately reproduced by our model. We find that the dust
disc is about 75% more extended but only half as high as the stellar disc. The
average face-on optical depth in the V-band is and the spread of
within our sample is quite substantial, which indicates that some spiral
galaxies are relatively opaque even when seen face-on.Comment: 18 pages, 6 figures, 4 tables, Accepted for publication in MNRA
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