109 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
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
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
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
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
Mass-concentration relation of clusters of galaxies from CFHTLenS
Based on weak lensing data from the Canada-France-Hawaii Telescope Lensing
Survey (CFHTLenS), in this paper we study the mass-concentration (-)
relation for redMaPPer clusters in the fields. We extract the
- relation by measuring the density profiles of individual clusters
instead of using stacked weak lensing signals. By performing Monte Carlo
simulations, we demonstrate that although the signal-to-noise ratio for each
individual cluster is low, the unbiased - relation can still be reliably
derived from a large sample of clusters by carefully taking into account the
impacts of shape noise, cluster center offset, dilution effect from member or
foreground galaxies, and the projection effect. Our results show that within
error bars the derived - relation for redMaPPer clusters is in agreement
with simulation predictions. There is a weak deviation in that the halo
concentrations calibrated by Monte Carlo simulations are somewhat higher than
that predicted from cosmology.Comment: Accepted for Publication in ApJ. 18 pages, 8 figures. Updated to
match the published versio
LEMON:LEns MOdelling with Neural networks - I. Automated modelling of strong gravitational lenses with Bayesian Neural Networks
The unprecedented number of gravitational lenses expected from new-generation facilities such as the ESA Euclid telescope and the Vera Rubin Observatory makes it crucial to rethink our classical approach to lens-modelling. In this paper, we present LEMON (Lens Modelling with Neural networks): a new machine-learning algorithm able to analyse hundreds of thousands of gravitational lenses in a reasonable amount of time. The algorithm is based on a Bayesian Neural Network: a new generation of neural networks able to associate a reliable confidence interval to each predicted parameter. We train the algorithm to predict the three main parameters of the singular isothermal ellipsoid model (the Einstein radius and the two components of the ellipticity) by employing two simulated data sets built to resemble the imaging capabilities of the Hubble Space Telescope and the forthcoming Euclid satellite. In this work, we assess the accuracy of the algorithm and the reliability of the estimated uncertainties by applying the network to several simulated data sets of 104 images each. We obtain accuracies comparable to previous studies present in the current literature and an average modelling time of just ∼0.5 s per lens. Finally, we apply the LEMON algorithm to a pilot data set of real lenses observed with HST during the SLACS program, obtaining unbiased estimates of their SIE parameters. The code is publicly available on GitHub (https://github.com/fab-gentile/LEMON).</p
CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations -- I. Constraining physical processes in local star-forming galaxies
We compare the structural properties and dark matter content of star-forming
galaxies taken from the CAMELS cosmological simulations to the observed trends
derived from the SPARC sample in the stellar mass range , to provide constraints on the value of
cosmological and astrophysical (SN- and AGN-related) parameters. We consider
the size-, internal DM fraction-, internal DM mass- and total-stellar mass
relations for all the 1065 simulations from the IllustrisTNG, SIMBA and ASTRID
suites of CAMELS, and search for the parameters that minimize the
with respect to the observations. For the IllustrisTNG suite, we find the
following constraints for the cosmological parameters: , and , which are consistent within with the results
from the nine-year WMAP observations. SN feedback-related astrophysical
parameters, which describe the departure of outflow wind energy per unit star
formation rate and wind velocity from the reference IllustrisTNG simulations,
assume the following values: and
, respectively. Therefore, simulations
with a lower value of outflow wind energy per unit star formation rate with
respect to the reference illustrisTNG simulation better reproduce the
observations. Simulations based on SIMBA and ASTRID suites predict central dark
matter masses substantially larger than those observed in real galaxies, which
can be reconciled with observations only by requiring values of
inconsistent with cosmological constraints for SIMBA, or
simulations characterized by unrealistic galaxy mass distributions for ASTRID.Comment: 24 pages, 10 figures, 9 tables. Accepted by MNRAS for publication;
Added a reference to sec. 4.
- …