725 research outputs found
Strong Gravitational Lensing and Dynamical Dark Energy
We study the strong gravitational lensing properties of galaxy clusters
obtained from N-body simulations with different kind of Dark Energy (DE). We
consider both dynamical DE, due to a scalar field self--interacting through
Ratra-Peebles (RP) or SUGRA potentials, and DE with constant negative w=p/rho=
-1 (LCDM). We have 12 high resolution lensing systems for each cosmological
model with a mass greater than 5x10^{14} solar masses. Using a Ray Shooting
technique we make a detailed analysis of the lensing properties of these
clusters with particular attention to the number of arcs and their properties
(magnification, length and width). We found that the number of giant arcs
produced by galaxy clusters changes in a considerable way from LCDM models to
Dynamical Dark Energy models with a RP or SUGRA potentials. These differences
originate from the different epochs of cluster formation and from the
non-linearity of the strong lensing effect. We suggest the Strong lensing is
one of the best tool to discriminate among different kind of Dark Energy.Comment: 8 pages, 11 figures. Lensing map resolution improved and effects of
resolution discussed. One more RP model analysed. Accepted for publication by
MNRA
The effect of low mass substructures on the Cusp lensing relation
It has been argued that the flux anomalies detected in gravitationally lensed
QSOs are evidence for substructures in the foreground lensing haloes. In this
paper we investigate this issue in greater detail focusing on the Cusp relation
which corresponds to images of a source located to the cusp of the inner
caustic curve. We use numerical simulations combined with a Monte Carlo
approach to study the effects of the expected power law distribution of
substructures within LCDM haloes on the multiple images.
Generally, the high number of anomalous flux ratios in the cusp
configurations is unlikely explained by 'simple' perturbers (subhaloes) inside
the lensing galaxy, either modeled by point masses or extended NFW subhaloes.
We considered in our analysis a mass range of 10^5-10^7 Msun for the subhaloes.
We also demonstrate that including the effects of the surrounding mass
distribution, such as other galaxies close to the primary lens, does not change
the results. We conclude that triple images of lensed QSOs do not show any
direct evidence for dark dwarf galaxies such as cold dark matter substructure.Comment: 10 pages, 19 figures, Effects of different subhalos concentrations
discussed, analysis improved, accepted by MNRA
The dependence of tidal stripping efficiency on the satellite and host galaxy morphology
In this paper we study the tidal stripping process for satellite galaxies
orbiting around a massive host galaxy, and focus on its dependence on the
morphology of both satellite and host galaxy. For this purpose, we use three
different morphologies for the satellites: pure disc, pure bulge and a mixture
bulge+disc. Two morphologies are used for the host galaxies: bulge+disc and
pure bulge. We find that while the spheroidal stellar component experiences a
constant power-law like mass removal, the disc is exposed to an exponential
mass loss when the tidal radius of the satellite is of the same order of the
disc scale length. This dramatic mass loss is able to completely remove the
stellar component on time scale of 100 Myears. As a consequence two satellites
with the same stellar and dark matter masses, on the same orbit could either
retain considerable fraction of their stellar mass after 10 Gyrs or being
completely destroyed, depending on their initial stellar morphology. We find
that there are two characteristic time scales describing the beginning and the
end of the disc removal, whose values are related to the size of the disc. This
result can be easily incorporated in semi-analytical models. We also find that
the host morphology and the orbital parameters also have an effect on the
determining the mass removal, but they are of secondary importance with respect
to satellite morphology. We conclude that satellite morphology has a very
strong effect on the efficiency of stellar stripping and should be taken into
account in modeling galaxy formation and evolution.Comment: 11 pages, 9 figures; accepted for publication in MNRA
Alas, the dark matter structures were not that trivial
The radial density profile of dark matter structures has been observed to
have an almost universal behaviour in numerical simulations, however, the
physical reason for this behaviour remains unclear. It has previously been
shown that if the pseudo phase-space density, rho/sigma_d^epsilon, is a
beautifully simple power-law in radius, with the "golden values" epsilon=3 and
d=r (i.e., the phase-space density is only dependent on the radial component of
the velocity dispersion), then one can analytically derive the radial variation
of the mass profile, dispersion profile etc. That would imply, if correct, that
we just have to explain why rho/sigma^3_r ~r^{-alpha}, and then we would
understand everything about equilibrated DM structures. Here we use a set of
simulated galaxies and clusters of galaxies to demonstrate that there are no
such golden values, but that each structure instead has its own set of values.
Considering the same structure at different redshifts shows no evolution of the
phase-space parameters towards fixed points. There is also no clear connection
between the halo virialized mass and these parameters. This implies that we
still do not understand the origin of the profiles of dark matter structures.Comment: 4 pages, 3 figures, accepted for publication in ApJ
A New Estimate of the Hubble Time with Improved Modeling of Gravitational Lenses
This paper examines free-form modeling of gravitational lenses using Bayesian
ensembles of pixelated mass maps. The priors and algorithms from previous work
are clarified and significant technical improvements are made. Lens
reconstruction and Hubble Time recovery are tested using mock data from simple
analytic models and recent galaxy-formation simulations. Finally, using
published data, the Hubble Time is inferred through the simultaneous
reconstruction of eleven time-delay lenses. The result is
H_0^{-1}=13.7^{+1.8}_{-1.0} Gyr.Comment: 24 pages, 9 figures. Accepted to Ap
Radial distribution and strong lensing statistics of satellite galaxies and substructure using high resolution LCDM hydrodynamical simulations
We analyse the number density and radial distribution of substructures and
satellite galaxies using cosmological simulations that follow the gas dynamics
of a baryonic component, including shock heating, radiative cooling and star
formation within the hierarchical concordance LCDM model. We find that the
dissipation of the baryons greatly enhances the survival of subhaloes,
expecially in the galaxy core, resulting in a radial distribution of satellite
galaxies that closely follows the overall mass distribution in the inner part
of the halo. Hydrodynamical simulations are necessary to resolve the adiabatic
contraction and dense cores of galaxies, resulting in a total number of
satellites a factor of two larger than found in pure dark matter simulation, in
good agreement with the observed spatial distribution of satellite galaxies
within galaxies and clusters. Convergence tests show that the cored
distribution found by previous authors in pure N-body simulations was due to
physical overmerging of dark matter only structures.
We proceed to use a ray-shooting technique in order to study the impact of
these additional substructures on the number of violations of the cusp caustic
magnification relation. We develop a new approach to try to disentangle the
effect of substructures from the intrinsic discreteness of N-Body simulations.
Even with the increased number of substructures in the centres of galaxies, we
are not able to reproduce the observed high numbers of discrepancies observed
in the flux ratios of multiply lensed quasars.Comment: 11 pages, 15 figures, comparison with previous works updated, one
more plot added, minor changes to match the accepted version by MNRA
Radial density profiles of time-delay lensing galaxies
We present non-parametric radial mass profiles for ten QSO strong lensing
galaxies. Five of the galaxies have profiles close to ,
while the rest are closer to r^{-1}, consistent with an NFW profile. The former
are all relatively isolated early-types and dominated by their stellar light.
The latter --though the modeling code did not know this-- are either in
clusters, or have very high mass-to-light, suggesting dark-matter dominant
lenses (one is a actually pair of merging galaxies). The same models give
H_0^{-1} = 15.2_{-1.7}^{+2.5}\Gyr (H_0 = 64_{-9}^{+8} \legacy), consistent
with a previous determination. When tested on simulated lenses taken from a
cosmological hydrodynamical simulation, our modeling pipeline recovers both H_0
and within estimated uncertainties. Our result is contrary to some
recent claims that lensing time delays imply either a low H_0 or galaxy
profiles much steeper than r^{-2}. We diagnose these claims as resulting from
an invalid modeling approximation: that small deviations from a power-law
profile have a small effect on lensing time-delays. In fact, as we show using
using both perturbation theory and numerical computation from a
galaxy-formation simulation, a first-order perturbation of an isothermal lens
can produce a zeroth-order change in the time delays.Comment: Replaced with final version accepted for publication in ApJ; very
minor changes to text; high resolution figures may be obtained at
justinread.ne
- …