3,952 research outputs found
On the lack of stellar bars in Coma dwarf galaxies
We present a study of the bar fraction in the Coma cluster galaxies based on
a sample of ~190 galaxies selected from the SDSS-DR6 and observed with the
Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). The
unprecedented resolution of the HST-ACS images allows us to explore the
presence of bars, detected by visual classification, throughout a luminosity
range of 9 mag (-23 < M_r < -14), permitting us to study the poor known region
of dwarf galaxies. We find that bars are hosted by galaxies in a tight range of
both luminosities (-22 < M_r < -17) and masses (10^9 < M*/Msun < 10^11). In
addition, we find that the bar fraction does not vary significantly when going
from the center to the cluster outskirts, implying that cluster environment
plays a second-order role in bar formation/evolution. The shape of the bar
fraction distribution with respect to both luminosity and mass is well matched
by the luminosity distribution of disk galaxies in Coma, indicating that bars
are good tracers of cold stellar disks.Comment: 2 pages, 1 figure, to appear in the proceedings of the conference "A
Universe of Dwarf Galaxies" (Lyon, June 14-18, 2010
A photometric analysis of Abell 1689: two-dimensional multi-structure decomposition, morphological classification, and the Fundamental Plane
We present a photometric analysis of 65 galaxies in the rich cluster Abell
1689 at , using the Hubble Space Telescope Advanced Camera for Surveys
archive images in the rest-frame -band. We perform two-dimensional
multi-component photometric decomposition of each galaxy adopting different
models of the surface-brightness distribution. We present an accurate
morphological classification for each of the sample galaxies. For 50 early-type
galaxies, we fit both a de Vaucouleurs and S\'ersic law; S0s are modelled by
also including a disc component described by an exponential law. Bars of SB0s
are described by the profile of a Ferrers ellipsoid. For the 15 spirals, we
model a S\'ersic bulge, exponential disc, and, when required, a Ferrers bar
component. We derive the Fundamental Plane by fitting 40 early-type galaxies in
the sample, using different surface-brightness distributions. We find that the
tightest plane is that derived by S\'ersic bulges. We find that bulges of
spirals lie on the same relation. The Fundamental Plane is better defined by
the bulges alone rather than the entire galaxies. Comparison with local samples
shows both an offset and rotation in the Fundamental Plane of Abell 1689.Comment: 53 pages, 71 figures, MNRAS in pres
Non Perturbative Renormalization Group, momentum dependence of -point functions and the transition temperature of the weakly interacting Bose gas
We propose a new approximation scheme to solve the Non Perturbative
Renormalization Group equations and obtain the full momentum dependence of
-point functions. This scheme involves an iteration procedure built on an
extension of the Local Potential Approximation commonly used within the Non
Perturbative Renormalization Group. Perturbative and scaling regimes are
accurately reproduced. The method is applied to the calculation of the shift
in the transition temperature of the weakly repulsive Bose gas, a
quantity which is very sensitive to all momenta intermediate between these two
regions. The leading order result is in agreement with lattice calculations,
albeit with a theoretical uncertainty of about 25%. The next-to-leading order
differs by about 10% from the best accepted result
Deep spectroscopic luminosity function of Abell 85: no evidence for a steep upturn of the faint-end slope
We present a new deep determination of the spectroscopic LF within the virial
radius of the nearby and massive Abell\,85 (A85) cluster down to the dwarf
regime (M* + 6) using VLT/VIMOS spectra for galaxies with m mag and mag arcsec. The
resulting LF from 438 cluster members is best modelled by a double Schechter
function due to the presence of a statistically significant upturn at the
faint-end. The amplitude of this upturn (),
however, is much smaller than that of the SDSS composite photometric cluster LF
by Popesso et al. 2006, -2. The faint-end slope of the LF in
A85 is consistent, within the uncertainties, with that of the field. The red
galaxy population dominates the LF at low luminosities, and is the main
responsible for the upturn. The fact that the slopes of the spectroscopic LFs
in the field and in a cluster as massive as A85 are similar suggests that the
cluster environment does not play a major role in determining the abundance of
low-mass galaxies.Comment: 6 pages, 4 figures, accepted at MNRAS lette
Doorway States and Billiards
Whenever a distinct state is immersed in a sea of complicated and dense
states, the strength of the distinct state, which we refer to as a doorway, is
distributed in their neighboring states. We analyze this mechanism for 2-D
billiards with different geometries. One of them is symmetric and integrable,
another is symmetric but chaotic, and the third has a capricious form. The fact
that the doorway-state mechanism is valid for such highly diverse cases, proves
that it is robust.Comment: 7 pages, 6 figures, Accepted in Proceedings of "Symmetries in
Nature", Symposium in Memoriam Marcos Moshinsk
Mesoscopic non-equilibrium thermodynamics approach to non-Debye dielectric relaxation
Mesoscopic non-equilibrium thermodynamics is used to formulate a model
describing non-homogeneous and non-Debye dielectric relaxation. The model is
presented in terms of a Fokker-Planck equation for the probability distribution
of non-interacting polar molecules in contact with a heat bath and in the
presence of an external time-dependent electric field. Memory effects are
introduced in the Fokker-Planck description through integral relations
containing memory kernels, which in turn are used to establish a connection
with fractional Fokker-Planck descriptions. The model is developed in terms of
the evolution equations for the first two moments of the distribution function.
These equations are solved by following a perturbative method from which the
expressions for the complex susceptibilities are obtained as a functions of the
frequency and the wave number. Different memory kernels are considered and used
to compare with experiments of dielectric relaxation in glassy systems. For the
case of Cole-Cole relaxation, we infer the distribution of relaxation times and
its relation with an effective distribution of dipolar moments that can be
attributed to different segmental motions of the polymer chains in a melt.Comment: 33 pages, 6 figure
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