633 research outputs found
The mass-concentration relation in massive galaxy clusters at redshift ~1
Mass and concentration of clusters of galaxies are related and evolving with
redshift. We study the properties of a sample of 31 massive galaxy clusters at
high redshift, 0.8 < z < 1.5, using weak and strong lensing observations.
Concentration is a steep function of mass, c_{200} ~M_{200}^{-0.83 +-0.39},
with higher-redshift clusters being less concentrated. Mass and concentration
from the stacked analysis, M_{200}=(4.1+-0.4)x10^{14}M_Sun/h and
c_{200}=2.3+-0.2, are in line with theoretical results extrapolated from the
local universe. Clusters with signs of dynamical activity preferentially
feature high concentrations. We discuss the possibility that the whole sample
is a mix of two different kinds of haloes. Over-concentrated clusters might be
accreting haloes out of equilibrium in a transient phase of compression,
whereas less concentrated ones might be more relaxed.Comment: 10 pages, 3 figures; in press on MNRA
A multi-wavelength study of the gravitational lens COSMOS J095930+023427
We present a multi-wavelength study of the gravitational lens COSMOS
J095930+023427 (z=0.89), together with the associated galaxy group located at
along the line of sight and the lensed background galaxy.
The source redshift is currently unknown, but estimated to be at . The analysis is based on the available public HST, Subaru, Chandra imaging
data, and VLT spectroscopy. The lensing system is an early-type galaxy showing
a strong [OII] emission line, and produces 4 bright images of the distant
background source. It has an Einstein radius of 0.79", about 4 times large than
the effective radius. We perform a lensing analysis using both a Singular
Isothermal Ellipsoid (SIE) and a Peudo-Isothermal Elliptical Mass Distribution
(PIEMD) for the lensing galaxy, and find that the final results on the total
mass, the dark matter (DM) fraction within the Einstein radius and the external
shear due to a foreground galaxy group are robust with respect of the choice of
the parametric model and the source redshift (yet unknown). We measure the
luminous mass from the photometric data, and find the DM fraction within the
Einstein radius to be between and ,
depending on the unknown source redshift. Meanwhile, the non-null external
shear found in our lensing models supports the presence and structure of a
galaxy group at , and an independent measurement of the 0.5-2 keV
X-ray luminosity within 20" around the X-ray centroid provides a group mass of
M, in good agreement with the previous
estimate derived through weak lensing analysis.Comment: 13 pages, 6 figure
Measurement of the halo bias from stacked shear profiles of galaxy clusters
We present the observational evidence of the 2-halo term in the stacked shear
profile of a sample of about 1200 optically selected galaxy clusters based on
imaging data and the public shear catalog from the CFHTLenS. We find that the
halo bias, a measure of the correlated distribution of matter around galaxy
clusters, has amplitude and correlation with galaxy cluster mass in very good
agreement with the predictions based on the LCDM standard cosmological model.
The mass-concentration relation is flat but higher than theoretical
predictions. We also confirm the close scaling relation between the optical
richness of galaxy clusters and their mass.Comment: 5 pages, 4 figures. In press on ApJ Letter
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
PSZ2LenS. Weak lensing analysis of the Planck clusters in the CFHTLenS and in the RCSLenS
The possibly unbiased selection process in surveys of the Sunyaev Zel'dovich
effect can unveil new populations of galaxy clusters. We performed a weak
lensing analysis of the PSZ2LenS sample, i.e. the PSZ2 galaxy clusters detected
by the Planck mission in the sky portion covered by the lensing surveys
CFHTLenS and RCSLenS. PSZ2LenS consists of 35 clusters and it is a
statistically complete and homogeneous subsample of the PSZ2 catalogue. The
Planck selected clusters appear to be unbiased tracers of the massive end of
the cosmological haloes. The mass concentration relation of the sample is in
excellent agreement with predictions from the Lambda cold dark matter model.
The stacked lensing signal is detected at 14 sigma significance over the radial
range 0.1<R<3.2 Mpc/h, and is well described by the cuspy dark halo models
predicted by numerical simulations. We confirmed that Planck estimated masses
are biased low by b_SZ= 27+-11(stat)+-8(sys) per cent with respect to weak
lensing masses. The bias is higher for the cosmological subsample, b_SZ=
40+-14+-(stat)+-8(sys) per cent.Comment: v1: 23 pages. Comments are welcome. v2: 27 pages, in press on MNRAS.
Expanded discussion on systematics and lensing average
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
Source plane reconstruction of the giant gravitational arc in Abell 2667: a candidate Wolf-Rayet galaxy at z~1
We present a new analysis of HST, Spitzer telescope imaging and VLT imaging
and spectroscopic data of a bright lensed galaxy at =1.0334 in the lensing
cluster Abell~2667. Using this high-resolution imaging we present an updated
lens model that allows us to fully understand the lensing geometry and
reconstruct the lensed galaxy in the source plane. This giant arc gives a
unique opportunity to peer into the structure of a high-redshift disk galaxy.
We find that the lensed galaxy of Abell 2667 is a typical spiral galaxy with
morphology similar to the structure of its counterparts at higher redshift
. The surface brightness of the reconstructed source galaxy in the
z band reveals the central surface brightness mag
arcsec and the characteristic radius kpc at redshift
. The morphological reconstruction in different bands shows obvious
negative radial color gradients for this galaxy. Moreover, the redder central
bulge tends to contain a metal-rich stellar population, rather than being
heavily reddened by dust due to high and patchy obscuration. We analyze the
VIMOS/IFU spectroscopic data and find that, in the given wavelength range
( \AA), the combined arc spectrum of the source galaxy is
characterized by a strong continuum emission with strong UV absorption lines
(FeII and MgII) and shows the features of a typical starburst Wolf-Rayet galaxy
NGC5253. More specifically, we have measured the EWs of FeII and MgII lines in
the Abell 2667 spectrum, and obtained similar values for the same wavelength
interval of the NGC5253 spectrum. Marginal evidence for CIII] 1909 emission at
the edge of the grism range further confirms our expectation.Comment: 20 pages, 7 figures, 1 table, accepted by the Astronomical Journa
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