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The overall objective of this study is to investigate claims found in the literature that fossil groups, characterized by a large magnitude gap between their two brightest galaxies, are darker, i.e. exhibit higher mass-to-light (M/L) ratios, compared to regular groups. Specifically, we aim to measure the mass of these systems using the weak gravitational lensing technique. To achieve this, we obtained deep images of four fossil systems with the CFHT telescope in the |$r$| and g bands. Through a careful process of weak gravitational shear measurement, including corrections for the point spread function (PSF) and contamination from group and foreground galaxies, we fit NFW models and obtained mass measurements as a result. Similarly, we quantified the light distribution produced by these groups, taking into account relevant data gaps in the images due to the presence of bright stars, as well as contamination from foreground and background galaxies. We obtained masses and M/L ratios that are consistent with previous results where mass was estimated from galaxy dynamics. Indeed, the four fossil systems studied here exhibit high M/L ratios compared to the general population of systems. Drawing more generalizable conclusions from a sample of only four systems is challenging. However, the procedure outlined in this study can be applied to large image surveys, allowing for a revisiting of this question with significantly reduced statistical uncertainties. This will enable a more homogeneous comparison between fossil groups and clusters and the overall population. [ABSTRACT FROM AUTHOR]

We present here new insights about the merging galaxy cluster Abell 2034 (⁠|$\bar{z}=0.114$|⁠) based on a combined weak lensing and dynamical analysis. From our deep Subaru BRC |$z$| ′ images plus Gemini–GMOS/N low-resolution spectra accompanied by available redshift data, we have obtained the individual masses of the colliding subclusters as well as estimated a timeline of the process. The collision event happened |$0.56^{+0.15}_{-0.22}$| Gyr ago between the subclusters A2034S (⁠|$M_{200}^S=2.35_{-0.99}^{+0.84}\times 10^{14}$| M⊙) and A2034N (⁠|$M_{200}^N = 1.08_{-0.71}^{+0.51} \times 10^{14}$| M⊙) with the gas content of both subclusters displaced in relation to their galaxy and dark matter distributions, in a scenario similar to that found in the Bullet Cluster. Following our data and modelling the collision event is, most likely, taking place not so far from the plane of the sky, with an angle of 27° ± 14° in relation to that. In spite of the intrinsic degeneracy inherent to the system (whether it has been observed incoming or outgoing), the comparison of our calculated time since the closest approximation with the estimated age of the observed X-ray shock front and the increment experienced by the velocity dispersion of the galaxy cluster members point towards an outgoing movement. Besides, we found a strong evidence for the presence of a third structure that we called A2034W. [ABSTRACT FROM AUTHOR]

The galaxy cluster Abell 3376 is a nearby (z = 0.046) dissociative merging cluster surrounded by two prominent radio relics and showing an X-ray comet-like morphology. The merger system is comprised of the subclusters A3376W and A3376E. Based on new deep multiwavelength large-field images and published redshifts, we bring new insights about the history of this merger. Despite the difficulty of applying the weak lensing technique at such low redshift, we successfully recovered the mass distribution in the cluster field. Moreover, with the application of a two-body model, we have addressed the dynamics of this merging system. We have found the individual masses of M200W= 3.0-1.7+1.3 × 1014 M⊚ and M200E= 0.9-0.8+0.5 × 1014 M⊚. The cometary-shaped X-ray distribution shows only one peak spatially coincident with both eastern BCG and the A3376E mass peak whereas the gas content of A3376W seems to be stripped out. Our data allowed us to confirm the existence of a third subcluster located at the north, 1147 ± 62 kpc apart from the neighbour subcluster A3376E and having a mass MN200 = 1.4-1.0+0.7 × 1014 M⊚. From our dynamical analysis, we found the merging is taking place very close to the plane of the sky, with the merger axis just 10° ± 11° from it. The application of a two-body analysis code showed that the merging cluster is seen 0.9-0.3+0.2 Gyr after the pericentric passage and it is currently going to the point of maximum separation between the subclusters. [ABSTRACT FROM AUTHOR]

We present a stacked weak-lensing analysis of 27 richness selected galaxy clusters at 0.40 彽 z ⩽ 0.62 in the COnstrain Dark Energy with X-ray galaxy clusters (CODEX) survey. The fields were observed in five bands with the Canada-France-Hawaii Telescope (CFHT). We measure the stacked surface mass density profile with a 14σ significance in the radial range 0.1 < R Mpc h-1 < 2.5. The profile is well described by the halo model, with the main halo term following a Navarro-Frenk-White profile (NFW) profile and including the off-centring effect. We select the background sample using a conservative colour-magnitude method to reduce the potential systematic errors and contamination by cluster member galaxies. We perform a Bayesian analysis for the stacked profile and constrain the best-fitting NFW parameters M200c = 6.6+1.0 -0.8 × 10>14 h -1M☉ and c200c = 3.7+0.7 -0.6. The off-centring effect was modelled based on previous observational results found for redMaPPer Sloan Digital Sky Survey clusters. Our constraints on M200c and c200c allow us to investigate the consistency with numerical predictions and select a concentration-mass relation to describe the high richness CODEX sample. Comparing our best-fitting values forM200c and c200c with other observational surveys at different redshifts, we find no evidence for evolution in the concentration-mass relation, though it could be mitigated by particular selection functions. Similar to previous studies investigating the X-ray luminosity-mass relation, our data suggest a lower evolution than expected from self-similarity. [ABSTRACT FROM AUTHOR]

We present a weak-lensing and dynamical study of the complex cluster Abell 1758 (A1758, z = 0.278) supported by hydrodynamical simulations. This cluster is composed of two main structures called A1758N and A1758S. The northern structure is composed of A1758NW and A1758NE, with lensing determined masses of 7.90+1.89 -1.55 × 1014 M☉ and 5.49+1.67 -1.33 × 1014 M☉, respectively. They show a remarkable feature: while in A1758NW, there is a spatial agreement among weak-lensing mass distribution, intracluster medium and its brightest cluster galaxy (BCG), in A1758NE, the X-ray peak is located 96+14 -15 arcsec away from the mass peak and BCG positions. Given the detachment between gas and mass, we could use the local surface mass density to estimate an upper limit for the dark matter self-interaction cross-section: σ/m < 5.83 cm2 g-1. Combining our velocity data with hydrodynamical simulations, we have shown that A1758 NW and NE had their closest approach 0.27 Gyr ago and their merger axis is 21° ± 12° from the plane of the sky. In the A1758S system, we have measured a total mass of 4.96+1.08 -1.19 × 1014 M☉ and, using radial velocity data, we found that the main merger axis is located at 70° ± 4° from the plane of the sky, therefore closest to the line of sight. [ABSTRACT FROM AUTHOR]

We present an axially symmetric formula to calculate the probability of finding gravitational arcs in galaxy clusters, being induced by their massive dark matter haloes, as a function of clusters redshifts and virial masses. The formula includes the ellipticity of the clusters dark matter potential by using a pseudo-elliptical approximation. The probabilities are calculated and compared for two dark-matter halo profiles, the Navarro, Frenk and White (NFW) and the Non-Singular-Isothermal-Sphere (NSIS). We demonstrate the power of our formulation through a Kolmogorov-Smirnov (KS) test on the strong lensing statistics of an X-ray bright sample of low redshift Abell clusters. This KS test allows to establish limits on the values of the concentration parameter for the NFW profile (cΔ) and the core radius for the NSIS profile (rc), which are related to the lowest cluster redshift (zcut) where strong arcs can be observed. For NFW dark matter profiles, we infer cluster haloes with concentrations that are consistent to those predicted by ΛCDM simulations. As for NSIS dark matter profiles, we find only upper limits for the clusters core radii and thus do not rule out a purely SIS model. For alternative mass profiles, our formulation provides constraints through zcut on the parameters that control the concentration of mass in the inner region of the clusters haloes. We find that zcut is expected to lie in the 0.0-0.2 redshift, highlighting the need to include very low-zz clusters in samples to study the clusters mass profiles. [ABSTRACT FROM AUTHOR]