4,953 research outputs found
Gravitational lensing and dynamics in SL2S\,J02140-0535: Probing the mass out to large radius
We aim to probe the mass of SL2S\,J02140-0535, a galaxy group at = 0.44
from the Strong Lensing Legacy Survey (SL2S). We combine strong lensing
modeling and dynamical constraints. The strong lensing analysis is based on
multi-band HST/ACS observations exhibiting strong lensing features that we have
followed-up spectroscopically with VLT/FORS2. To constrain the scale radius of
an NFW mass profile that cannot be constrained by strong lensing, we propose a
new method by taking advantage of the large-scale dynamical information
provided by VLT/FORS2 and KECK/LRIS spectroscopy of group members. In constrast
to other authors, we show that the observed lensing features in
SL2S\,J02140-0535 belong to different background sources: one at = 1.7
0.1 produces three images, while the other at = 1.023 0.001 has
only a single image. Our unimodal NFW mass model reproduces these images very
well. It is characterized by a concentration parameter = 6.0
0.6, which is slightly greater than the value expected from CDM
simulations for a mass of M 1 10 M_{\sun}.
The spectroscopic analysis of group members also reveals a unimodal structure
that exhibits no evidence of merging. We compare our dynamic mass estimate with
an independent weak-lensing based mass estimate finding that both are
consistent. Our combined lensing and dynamical analysis of SL2S\,J02140-0535
demonstrates the importance of spectroscopic information in reliably
identifying the lensing features. Our findings argue that the system is a
relaxed, massive galaxy group where mass is traced by light. This work shows a
potentially useful method for constraining large-scale properties inaccessible
to strong lensing, such as the scale radius of the NFW profile.Comment: Accepted for publication in A&
SARCS strong lensing galaxy groups: I - optical, weak lensing, and scaling laws
We present the weak lensing and optical analysis of the SL2S-ARCS (SARCS)
sample of strong lens candidates. The sample is based on the Strong Lensing
Legacy Survey (SL2S), a systematic search of strong lensing systems in the
photometric Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The SARCS
sample focuses on arc-like features and is designed to contain mostly galaxy
groups. We briefly present the weak lensing methodology that we use to estimate
the mass of the SARCS objects. Among 126 candidates, we obtain a weak lensing
detection for 89 objects with velocity dispersions of the Singular Isothermal
Sphere mass model ranging from 350 to 1000 km/s with an average value of
600km/s, corresponding to a rich galaxy group (or poor cluster). From the
galaxies belonging to the bright end of the group's red sequence (M_i<-21), we
derive the optical properties of the SARCS candidates. We obtain typical
richnesses of N=5-15 galaxies and optical luminosities of L=0.5-1.5e+12 Lsol
(within a radius of 0.5 Mpc). We use these galaxies to compute luminosity
density maps, from which a morphological classification reveals that a large
fraction of the sample are groups with a complex light distribution, either
elliptical or multimodal, suggesting that these objects are dynamically young
structures. We finally combine the lensing and optical analyses to draw a
sample of 80 most secure group candidates, i.e. weak lensing detection and
over-density at the lens position in the luminosity map, to remove false
detections and galaxy-scale systems from the initial sample. We use this
reduced sample to probe the optical scaling relations in combination with a
sample of massive galaxy clusters. We detect the expected correlations over the
probed range in mass with a typical scatter of 25% in the SIS velocity
dispersion at a given richness or luminosity, making these scaling laws
interesting mass proxie
A complex state transition from the black hole candidate Swift J1753.5-0127
We present our monitoring campaign of the outburst of the black-hole
candidate Swift J1753.5-0127, observed with the Rossi X-ray Timing Explorer and
the Swift satellites. After ~4.5 years since its discovery, the source had a
transition to the hard intermediate state. We performed spectral and timing
studies of the transition showing that, unlike the majority of the transient
black holes, the system did not go to the soft states but it returned to the
hard state after a few months. During this transition Swift J1753.5-0127
features properties which are similar to those displayed by the black hole
Cygnus X-1. We compared Swift J1753.5-0127 to one dynamically confirmed black
hole and two neutron stars showing that its power spectra are in agreement with
the binary hosting a black hole. We also suggest that the prolonged period at
low flux that followed the initial flare is reminiscent of that observed in
other X-ray binaries, as well as in cataclysmic variables.Comment: Accepted for publication in MNRA
Testing reflection features in 4U 1705-44 with XMM-Newton, BeppoSAX and RXTE in the hard and soft state
We use data of the bright atoll source 4U 1705-44 taken with XMM-Newton,
BeppoSAX and RXTE both in the hard and in the soft state to perform a
self-consistent study of the reflection component in this source. Although the
data from these X-ray observatories are not simultaneous, the spectral
decomposition is shown to be consistent among the different observations, when
the source flux is similar. We therefore select observations performed at
similar flux levels in the hard and soft state in order to study the spectral
shape in these two states in a broad band (0.1-200 keV) energy range, with good
energy resolution, and using self-consistent reflection models. These
reflection models provide a good fit for the X-ray spectrum both in the hard
and in the soft state in the whole spectral range. We discuss the differences
in the main spectral parameters we find in the hard and the soft state,
respectively, providing evidence that the inner radius of the optically thick
disk slightly recedes in the hard state.Comment: Accepted for publication in A&A, 20 pages, 12 figure
Strong lensing, weak lensing, and dynamics in SL2S J02140-0535
International audienceWe combine strong lensing modeling and dynamical constraints in order to probe the mass of SL2S J02140-0535, a galaxy group at z = 0.44 from the Strong Lensing Legacy Survey (SL2S) which has uncovered a new population of group-scale strong lenses. The strong lensing analysis is based on multi-band HST/ACS observations which display strong lensing features that we have followed up spectroscopically with VLT/FORS2. To constrain the scale radius of an NFW mass profile, we propose a new method taking advantage of the large scale dynamical information provided by VLT/FORS2 and KECK/LRIS spectroscopy of group members. This work shows a potentially useful method for constraining large-scale properties inaccessible to strong lensing, such as the scale radius of the NFW profile
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