440 research outputs found
Detecting planets around stars in nearby galaxies
The only way to detect planets around stars at distances of several kpc is by
(photometric or astrometric) microlensing observations. In this paper, we show
that the capability of photometric microlensing extends to the detection of
signals caused by planets around stars in nearby galaxies (e.g. M31) and that
there is no other method that can achieve this. Due to the large crowding,
microlensing experiments towards M31 can only observe the high-magnification
part of a lensing light curve. Therefore, the dominating channel for
microlensing signals by planets is in distortions near the peak of
high-magnification events as discussed by Griest and Safizadeh. We calculate
the probability to detect planetary anomalies for microlensing experiments
towards M31 and find that jupiter-like planets around stars in M31 can be
detected. Though the characterization of the planet(s) involved in this signal
will be difficult, the absence of such signals can yield strong constraints on
the abundance of jupiter-like planets.Comment: 16 LaTex Pages, including 1 Postscript Figures, submitted to A&A;
title changed, one more author added, completely revised version: central
point is detecting planet in nearby galaxies and one more technique is taken
into consideratio
Toward a detailed view on the kinematics of intermediate luminosity early-type galaxies no dark matter candidates
In several nearby intermediate luminosity early-type galaxies, recent
observations at large radii have shown a indications of a lack of dark matter,
substantially at odds with the prediction from the CDM hierarchical merger
models. Here we discuss a pilot observational project for the study of the
internal kinematical and dynamical properties of this remarkable sample of
galaxies. Using the VIMOS-IFU in its high spectral resolution mode, it would be
possible to investigate the regions up to about 1.2 effective radii, taking
advantage of the much larger field of view and telescope diameter. This will
allow to disclose the presence of any kinematical substructures which could
affect the conclusion on the mass modeling and definitely clarify the inner
structure of this particular class of early-type galaxies.Comment: 4 pages, 1 figure, Euro3D Science Workshop, Cambridge, May 2003, AN,
accepte
Mass - concentration relation and weak lensing peak counts
The statistics of peaks in weak lensing convergence maps is a promising tool
to investigate both the properties of dark matter haloes and constrain the
cosmological parameters. We study how the number of detectable peaks and its
scaling with redshift depend upon the cluster dark matter halo profiles and use
peak statistics to constrain the parameters of the mass - concentration (MC)
relation. We investigate which constraints the Euclid mission can set on the MC
coefficients also taking into account degeneracies with the cosmological
parameters. To this end, we first estimate the number of peaks and its redshift
distribution for different MC relations. We find that the steeper the mass
dependence and the larger the normalisation, the higher is the number of
detectable clusters, with the total number of peaks changing up to
depending on the MC relation. We then perform a Fisher matrix forecast of the
errors on the MC relation parameters as well as cosmological parameters. We
find that peak number counts detected by Euclid can determine the normalization
, the mass and redshift slopes and intrinsic scatter
of the MC relation to an unprecedented accuracy being
, , ,
if all cosmological parameters are assumed to
be known. Should we relax this severe assumption, constraints are degraded, but
remarkably good results can be restored setting only some of the parameters or
combining peak counts with Planck data. This precision can give insight on
competing scenarios of structure formation and evolution and on the role of
baryons in cluster assembling. Alternatively, for a fixed MC relation, future
peaks counts can perform as well as current BAO and SNeIa when combined with
Planck.Comment: 14 pages, 8 figures, accepted for publication on Astronomy &
Astrophysic
Evolution of central dark matter of early-type galaxies up to z ~ 0.8
We investigate the evolution of dark and luminous matter in the central
regions of early-type galaxies (ETGs) up to z ~ 0.8. We use a spectroscopically
selected sample of 154 cluster and field galaxies from the EDisCS survey,
covering a wide range in redshifts (z ~ 0.4-0.8), stellar masses ( ~ 10.5-11.5 dex) and velocity dispersions
( ~ 100-300 \, km/s). We obtain central dark matter (DM)
fractions by determining the dynamical masses from Jeans modelling of galaxy
aperture velocity dispersions and the from galaxy colours, and
compare the results with local samples. We discuss how the correlations of
central DM with galaxy size (i.e. the effective radius, ),
and evolve as a function of redshift, finding
clear indications that local galaxies are, on average, more DM dominated than
their counterparts at larger redshift. This DM fraction evolution with can
be only partially interpreted as a consequence of the size-redshift evolution.
We discuss our results within galaxy formation scenarios, and conclude that the
growth in size and DM content which we measure within the last 7 Gyr is
incompatible with passive evolution, while it is well reproduced in the
multiple minor merger scenario. We also discuss the impact of the IMF on our DM
inferences and argue that this can be non-universal with the lookback time. In
particular, we find the Salpeter IMF can be better accommodated by low redshift
systems, while producing stellar masses at high- which are unphysically
larger than the estimated dynamical masses (particularly for
lower- systems).Comment: 14 pages, 6 figures, 3 tables, MNRAS in pres
A Free-Form Lensing Grid Solution for A1689 with New Mutiple Images
Hubble Space Telescope imaging of the galaxy cluster Abell 1689 has revealed
an exceptional number of strongly lensed multiply-imaged galaxies, including
high-redshift candidates. Previous studies have used this data to obtain the
most detailed dark matter reconstructions of any galaxy cluster to date,
resolving substructures ~25 kpc across. We examine Abell 1689 (hereafter,
A1689) non-parametrically, combining strongly lensed images and weak
distortions from wider field Subaru imaging, and we incorporate member galaxies
to improve the lens solution. Strongly lensed galaxies are often locally
affected by member galaxies, however, these perturbations cannot be recovered
in grid based reconstructions because the lensing information is too sparse to
resolve member galaxies. By adding luminosity-scaled member galaxy deflections
to our smooth grid we can derive meaningful solutions with sufficient accuracy
to permit the identification of our own strongly lensed images, so our model
becomes self consistent. We identify 11 new multiply lensed system candidates
and clarify previously ambiguous cases, in the deepest optical and NIR data to
date from Hubble and Subaru. Our improved spatial resolution brings up new
features not seen when the weak and strong lensing effects are used separately,
including clumps and filamentary dark matter around the main halo. Our
treatment means we can obtain an objective mass ratio between the cluster and
galaxy components, for examining the extent of tidal stripping of the luminous
member galaxies. We find a typical mass-to-light ratios of M/L_B = 21 inside
the r<1 arcminute region that drops to M/L_B = 17 inside the r<40 arcsecond
region. Our model independence means we can objectively evaluate the
competitiveness of stacking cluster lenses for defining the geometric
lensing-distance-redshift relation in a model independent way.Comment: 23 pages with 25 figures Replced with MNRAS submitted version. Some
figures have been corrected and minor text edit
The GAP-TPC
Several experiments have been conducted worldwide, with the goal of observing
low-energy nuclear recoils induced by WIMPs scattering off target nuclei in
ultra-sensitive, low-background detectors. In the last few decades noble liquid
detectors designed to search for dark matter in the form of WIMPs have been
extremely successful in improving their sensitivities and setting the best
limits. One of the crucial problems to be faced for the development of large
size (multi ton-scale) liquid argon experiments is the lack of reliable and low
background cryogenic PMTs: their intrinsic radioactivity, cost, and borderline
performance at 87 K rule them out as a possible candidate for photosensors. We
propose a brand new concept of liquid argon-based detector for direct dark
matter search: the Geiger-mode Avalanche Photodiode Time Projection Chamber
(GAP-TPC) optimized in terms of residual radioactivity of the photosensors,
energy and spatial resolution, light and charge collection efficiencyComment: 7 pages, 5 figures, Accepted for publication on JINS
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