102 research outputs found
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
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
Concentration, Spin and Shape of Dark Matter Haloes as a Function of the Cosmological Model: WMAP1, WMAP3 and WMAP5 results
We investigate the effects of changes in the cosmological parameters between
the WMAP 1st, 3rd, and 5th year results on the structure of dark matter haloes.
We use a set of simulations that cover 5 decades in halo mass ranging from the
scales of dwarf galaxies (V_c ~30 km/s) to clusters of galaxies (V_c ~ 1000
km/s). We find that the concentration mass relation is a power law in all three
cosmologies. However the slope is shallower and the zero point is lower moving
from WMAP1 to WMAP5 to WMAP3. For haloes of mass log(M_200/Msun) = 10, 12, and
14 the differences in the concentration parameter between WMAP1 and WMAP3 are a
factor of 1.55, 1.41, and 1.29, respectively. As we show, this brings the
central densities of dark matter haloes in good agreement with the central
densities of dwarf and low surface brightness galaxies inferred from their
rotation curves, for both the WMAP3 and WMAP5 cosmologies. We also show that
none of the existing toy models for the concentration-mass relation can
reproduce our simulation results over the entire range of masses probed. In
particular, the model of Bullock et al (B01) fails at the higher mass end (M >
1e13 Msun), while the NFW model of Navarro, Frenk & White (1997) fails
dramatically at the low mass end (M < 1e12 Msun). We present a new model, based
on a simple modification of that of B01, which reproduces the
concentration-mass relations in our simulations over the entire range of masses
probed (1e10 Msun < M < 1e15 Msun). Haloes in the WMAP3 cosmology (at a fixed
mass) are more flatted compared to the WMAP1 cosmology, with a medium to long
axis ration reduced by ~10 %. Finally, we show that the distribution of halo
spin parameters is the same for all three cosmologies.Comment: 16 pages, 16 figures, references updated, minor changes. Accepted for
publication on MNRAS. WMAP5 simulations available upon reques
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
Tracing the Nature of Dark Energy with Galaxy Distribution
Dynamical Dark Energy (DE) is a viable alternative to the cosmological
constant. Yet, constructing tests to discriminate between Lambda and dynamical
DE models is difficult because the differences are not large. In this paper we
explore tests based on the galaxy mass function, the void probability function
(VPF), and the number of galaxy clusters. At high z the number density of
clusters shows large differences between DE models, but geometrical factors
reduce the differences substantially. We find that detecting a model dependence
in the cluster redshift distribution is a hard challenge. We show that the
galaxy redshift distribution is potentially a more sensitive characteristics.
We do so by populating dark matter halos in Nbody simulations with galaxies
using well-tested Halo Occupation Distribution (HOD). We also estimate the Void
Probability Function and find that, in samples with the same angular surface
density of galaxies in different models, the VPF is almost model independent
and cannot be used as a test for DE. Once again, geometry and cosmic evolution
compensate each other. By comparing VPF's for samples with fixed galaxy mass
limits, we find measurable differences.Comment: 12 pages, 11 figures, dependence on mass-luminosity relation
discussed, minor changes to match the accepted version by MNRA
Non linear predictions from linear theories in models with Dark Energy
We study the cluster mass function and its evolution in different models with
Dark Energy arising from a self--interacting scalar field, with Ratra-Peebles
and SUGRA potentials. Computations are based on a Press & Schechter
approximation. The mass functions we obtain are compared with results holding
for open models or models with Dark Energy due to a cosmological constant.
Evolution results, in the Dark Energy cases, closely approach open models.Comment: 13 pages, 3 new figures included, references added. Accepted for
pubblication in New Astronom
Modeling Luminosity-Dependent Galaxy Clustering Through Cosmic Time
We employ high-resolution dissipationless simulations of the concordance LCDM
cosmology to model the observed luminosity dependence and evolution of galaxy
clustering through most of the age of the universe, from z~5 to z~0. We use a
simple, non-parametric model which monotonically relates galaxy luminosities to
the maximum circular velocity of dark matter halos (V_max) by preserving the
observed galaxy luminosity function in order to match the halos in simulations
with observed galaxies. The novel feature of the model is the use of the
maximum circular velocity at the time of accretion, V_max,acc, for subhalos,
the halos located within virial regions of larger halos. We argue that for
subhalos in dissipationless simulations, V_max,acc reflects the luminosity and
stellar mass of the associated galaxies better than the circular velocity at
the epoch of observation, V_max,now. The simulations and our model L-V_max
relation predict the shape, amplitude, and luminosity dependence of the
two-point correlation function in excellent agreement with the observed galaxy
clustering in the SDSS data at z~0 and in the DEEP2 samples at z~1 over the
entire probed range of projected separations, 0.1<r_p/(Mpc/h)<10.0. In
particular, the small-scale upturn of the correlation function from the
power-law form in the SDSS and DEEP2 luminosity-selected samples is reproduced
very well. At z~3-5, our predictions also match the observed shape and
amplitude of the angular two-point correlation function of Lyman-break galaxies
(LBGs) on both large and small scales, including the small-scale upturn.Comment: 16 pages 11 figures, ApJ in pres
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