arXiv subjects

G. B. Lima Neto

Publications and source records attributed to G. B. Lima Neto.

At least 19 recordsLinked to original sources

arXiv2025

Galaxy groups in various evolutionary stages

The formation process of galaxy groups is not yet fully understood. In particular, that of fossil groups (FGs) is still under debate. Due to the relative rarity of FGs, large samples of such objects are still missing. The present paper aims to analyse the properties of groups in various evolutionary stages (FGs, "almost" FGs, and non-FGs), and to increase the sample of FG candidates. We have spectroscopically observed galaxies in four groups and ten candidate FGs detected in the Canada France Hawaii Telescope Legacy Survey. We searched for substructures by applying the Serna-Gerbal dendrogram method to analyse the dynamical structure of each group. By applying the FIREFLY software to the continuum and PIPE_VIS to the emission lines, we derived the stellar population properties in various regions for each group. A roughly continuous variation in properties is found between a group that is still building up (XCLASS 1330), a well-formed massive group (MCG+00-27-023), a dynamically complex non-FG (NGC 4065), and a near-FG (NGC 4104). We also optically confirm two FGs in the Canada France Hawaii Telescope Legacy Survey, but their X-ray luminosity is still unknown. We observe that the lower the mass of the substructure, the more recent the stellar population in the considered groups. We also show an apparent lack of high-mass substructures for low-metallicity systems. These results are consistent with the generally adopted model of energy transfer during interactions of the galaxies with the group and cluster potential wells. Furthermore, the fossil status of a group might be related to the large-scale environment. Therefore, studying the positions of non-FGs, near-FGs, and FGs within the cosmic web can provide insights into the process of how fossil systems come into being in the Universe.

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arXiv2025

Structure and kinematics of the interacting group NGC 5098/5096

Most galaxies in the Universe are found in groups, which have various morphologies and dynamical states. Studying how groups evolve is an important step for our understanding in both large-scale structure formation and galaxy evolution. We analysed the system composed by two groups at z = 0.037, NGC 5098, a group dominated by a pair of elliptical galaxies, and NGC 5096, a compact system which appears to be interacting with NGC 5098. We aim to describe its current dynamical state in order to investigate how it fits in our current cosmological framework. Our analysis is based on deep Canada-France-Hawaii Telescope (CFHT/MegaCam) g and r imaging, archival Chandra X-ray data, and publicly available data of the galaxy redshift distribution. We model the surface brightness of the 12 brightest galaxies in the field-of-view and investigate the diffuse intragroup light that we detect. With a redshift sample of 112 galaxies, we study the dynamical states of both groups. We detect low surface brightness diffuse light associated with both galaxy-galaxy interactions and a possible group-group collision. The substructure we found in velocity space indicates a past interaction between both groups. This is further corroborated by the X-ray analysis. We conclude that NGC 5098 and NGC 5096 form a complex system, that may have collided in the past, producing a sloshing observed in X-rays and a large scale diffuse component of intragroup light as well as some important tidal debris.

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arXiv2023

The active CGCG 077-102 NED02 galaxy within the Abell 2063 galaxy cluster

Within the framework of investigating the link between central super massive black holes in the core of galaxies and the galaxies themselves, we detected a variable X-ray source in the center of CGCG 077-102 NED02, member of the CGCG 077-102 galaxy pair within the Abell 2063 galaxy cluster. Our goal was then to combine X-ray and optical data to demonstrate that this object harbors an active super massive black hole in its core, and to relate this to the dynamical status of the galaxy pair within the Abell 2063 cluster. We used Chandra and XMM-Newton archival data to derive the X-ray spectral shape and variability. We also obtained optical spectroscopy to detect the expected emission lines that are typically found in Active Galactic Nuclei. And we finally used public ZTF imaging data to investigate the optical variability. There is no evidence of multiple X-ray sources or extended component within CGCG 077-102 NED02. Single X-ray spectral models fit well the source. Non-random significant X-ray flux inter-observation X-ray variabilities were detected, between ~4days for short term variations and up to ~700days for long term variations. Optical spectroscopy points toward a passive galaxy for CGCG 077-102 NED01 and a Seyfert for CGCG 077-102 NED02. We did not detect short-term variability in the optical ZTF light curves. However, we found a significant long-term stochastic variability in the g-band that can be well described by the damped random walk model. Finally, the CGCG 077-102 galaxy pair is deeply embedded within the Abell 2063 potential, and has underwent the cluster influence for a long time. Our observations point toward a moderatly massive black hole in the center of CGCG 077-102 NED02, of ~10^6 Msol. CGCG 077-102 NED02 is not heavily obscured, perhaps due to surrounding intra cluster medium ram pressure stripping.

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arXiv2020

NGC 4104: a shell galaxy in a forming fossil group

Groups are the most common association of galaxies in the Universe, found in different configuration states such as loose, compact and fossil groups. We have studied the galaxy group MKW 4s, dominated by the giant early-type galaxy NGC 4104 at z=0.0282. Our aim was to understand the evolutionary stage of this group and to place it within the framework of the standard LambdaCDM cosmological scenario. We have obtained deep optical data with CFHT/Megacam (g and r bands) and we have applied both the galfit 2D image fitting program and the IRAF/ellipse 1D radial method to model the brightest group galaxy (BGG) and its extended stellar envelope. We have also analysed publicly available XMM-Newton and Chandra X-ray data. From N-body simulations of dry-mergers with different mass ratios of the infalling galaxy, we could constrain the dynamical stage of this system. Our results show a stellar shell system feature in NGC 4104 and an extended envelope that was reproduced by our numerical simulations of a collision with a satellite galaxy about 4--6 Gyr ago. The initial pair of galaxies had a mass ratio of at least 1:3. Taking into account the stellar envelope contribution to the total r band magnitude and the X-ray luminosity, MKW 4s falls into the category of a fossil group. Our results show that we are witnessing a rare case of a shell elliptical galaxy in a forming fossil group.

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arXiv2020

Simulations of gas sloshing induced by a newly discovered gas poor substructure in galaxy cluster Abell 1644

Collision events lead to peculiar morphologies in the intracluster gas of galaxies clusters. That seems to be the case of Abell 1644, a nearby galaxy cluster, composed of three main structures: the southern cluster that exhibits a spiral-like morphology, A1644S; the northern cluster seen in X-ray observations, A1644N1; and the recently discovered substructure, A1644N2. By means of $N$-body hydrodynamical simulations, we attempt to reconstruct the dynamical history of this system. These simulations resulted in two specific scenarios: (i) The collision between A1644S and A1644N2. Our best model has an inclination between the merger plane and the plane of the sky of $30^\circ$, and reaches the best morphology $1.6\,$Gyr after the pericentric passage. At this instant A1644N2 is gas poor, becoming nearly undetectable in X-ray emission. This model shows a good agreement with observations; (ii) The collision between A1644S and A1644N1. This approach did not give rise to results as satisfactory as the first scenario, due to great disturbances in density and mismatching temperature maps. As a complementary study, we perform a three-cluster simulation using as base the best-fitting model to reproduce the current state of A1644 with the three main structures. This scenario presented a good agreement to the global morphology of the observations. Thus, we find that the more likely scenario is a collision between A1644S and the newly discovered A1644N2, where A1644N1 may be present as long as it does not greatly interfere in the formation of the spiral feature.

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arXiv2020

Revising the merger scenario of the galaxy cluster Abell 1644: a new gas poor structure discovered by weak gravitational lensing

The galaxy cluster Abell 1644 ($\bar{z}=0.047$) is known for its remarkable spiral-like X-ray emission. It was previously identified as a bimodal system, comprising the subclusters, A1644S and A1644N, each one centered on a giant elliptical galaxy. In this work, we present a comprehensive study of this system, including new weak-lensing and dynamical data and analysis plus a tailor-made hydrodynamical simulation. The lensing and galaxy density maps showed a structure in the North that could not be seen on the X-ray images. We, therefore, rename the previously known northern halo as A1644N1 and the new one as A1644N2. Our lensing data suggests that those have fairly similar masses: $M_{200}^{\rm N1}=0.90_{-0.85}^{+0.45} \times10^{14}$ and $M_{200}^{\rm N2}=0.76_{-0.75}^{+0.37} \times10^{14}$ M$_\odot$, whereas the southern structure is the main one: $M_{200}^{\rm S}=1.90_{-1.28}^{+0.89}\times 10^{14}$ M$_\odot$. Based on the simulations, fed by the observational data, we propose a scenario where the remarkable X-ray characteristics in the system are the result of a collision between A1644S and A1644N2 that happened $\sim$1.6 Gyr ago. Currently, those systems should be heading to a new encounter, after reaching their maximum separation.

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arXiv2018

J-PLUS: On the identification of new cluster members in the double galaxy cluster A2589 & A2593 using PDFs

We aim to use multi-band imaging from the Phase-3 Verification Data of the J-PLUS survey to derive accurate photometric redshifts (photo-z) and look for potential new members in the surroundings of the nearby galaxy clusters A2589 (z=0.0414) & A2593 (z=0.0440), using redshift probability distribution functions. The ultimate goal is to demonstrate the usefulness of a 12-band filter system in the study of large-scale structure in the local universe. We present an optimized pipeline for the estimation of photo-z in clusters of galaxies. We tested our photo-z with a sample of 296 spectroscopically confirmed cluster members with a magnitude of = 16.6 and redshift =0.041. The combination of seven narrow and five broadband filters with a typical photometric-depth of r<21.5 provides dz/(1+z)=0.01 photo-z estimates. A precision of dz/(1+z)=0.005 is obtained for the 177 galaxies brighter than magnitude r<17. To foresee the precision beyond the spectroscopic sample, we designed a set of simulations in which real cluster galaxies are modeled and reinjected inside the images at different signal-to-noise. A precision of dz/(1+z)=0.02 and dz/(1+z)=0.03 is expected at = 18-22, respectively. Complementarily, we used SDSS/DR12 data to derive photo-z estimates for the same galaxy sample, demonstrating that the wavelength-resolution of the J-PLUS can double the precision achieved by SDSS for galaxies with a high S/N. We find as much as 170 new candidates across the entire field. The spatial distribution of these galaxies may suggest an overlap between the systems with no evidence of a clear filamentary structure connecting the clusters. These preliminary results show the potential of J-PLUS data to revisit membership of groups and clusters from nearby galaxies, important for the determination of luminosity and mass functions and environmental studies at the intermediate and low-mass regime.

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arXiv2015

Two spectroscopically confirmed galaxy structures at z=0.61 and 0.74 in the CFHTLS Deep~3 field

Adami et al. (2010) have detected several cluster candidates at z>0.5 as part of a systematic search for clusters in the Canada France Hawaii Telescope Legacy Survey, based on photometric redshifts. We focus here on two of them, located in the D3 field: D3-6 and D3-43. We have obtained spectroscopy with Gemini/GMOS and measured redshifts for 23 and 14 galaxies in the two structures. These redshifts were combined with those available in the literature. A dynamical and a weak lensing analysis were also performed, together with the study of X-ray Chandra archive data. Cluster D3-6 is found to be a single structure of 8 spectroscopically confirmed members at an average redshift z=0.607, with a velocity dispersion of 423 km/s. It appears to be a relatively low mass cluster. D3-43-S3 has 46 spectroscopically confirmed members at an average redshift z=0.739. It can be decomposed into two main substructures, having a velocity dispersion of about 600 and 350 km/s. An explanation to the fact that D3-43-S3 is detected through weak lensing (only marginally, at the ~3sigma level) but not in X-rays could be that the two substructures are just beginning to merge more or less along the line of sight. We also show that D3-6 and D3-43-S3 have similar global galaxy luminosity functions, stellar mass functions, and star formation rate (SFR) distributions. The only differences are that D3-6 exhibits a lack of faint early type galaxies, a deficit of extremely high stellar mass galaxies compared to D3-43-S3, and an excess of very high SFR galaxies. This study shows the power of techniques based on photometric redshifts to detect low to moderately massive structures, even at z~0.75.

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arXiv2014

The red sequence of Abell X-ray underluminous clusters

We present an analysis of the colour-magnitude relation for a sample of 56 X-ray underluminous Abell clusters, aiming to unveil properties that may elucidate the evolutionary stages of the galaxy populations that compose such systems. To do so, we compared the parameters of their colour-magnitude relations with the ones found for another sample of 50 "normal" X-ray emitting Abell clusters, both selected in an objective way. The $g$ and $r$ magnitudes from the SDSS-DR7 were used for constructing the colour-magnitude relations. We found that both samples show the same trend: the red sequence slopes change with redshift, but the slopes for X-ray underluminous clusters are always flatter than those for the normal clusters, by a difference of about 69% along the surveyed redshift range of 0.05 $\le z <$ 0.20. Also, the intrinsic scatter of the colour-magnitude relation was found to grow with redshift for both samples but, for the X-ray underluminous clusters, this is systematically larger by about 28%. By applying the Cramér test to the result of this comparison between X-ray normal and underluminous cluster samples, we get probabilities of 92% and 99% that the red sequence slope and intrinsic scatter distributions, respectively, differ, in the sense that X-ray underluminous clusters red sequences show flatter slopes and higher scatters in their relations. No significant differences in the distributions of red-sequence median colours are found between the two cluster samples. This points to X-ray underluminous clusters being younger systems than normal clusters, possibly in the process of accreting groups of galaxies, individual galaxies and gas.

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arXiv2014

The mass profile and dynamical status of the z~0.8 galaxy cluster LCDCS 0504

Constraints on the mass distribution in high-redshift clusters of galaxies are not currently very strong. We aim to constrain the mass profile, M(r), and dynamical status of the $z \sim 0.8$ LCDCS 0504 cluster of galaxies characterized by prominent giant gravitational arcs near its center. Our analysis is based on deep X-ray, optical, and infrared imaging, as well as optical spectroscopy. We model the mass distribution of the cluster with three different mass density profiles, whose parameters are constrained by the strong lensing features of the inner cluster region, by the X-ray emission from the intra-cluster medium, and by the kinematics of 71 cluster members. We obtain consistent M(r) determinations from three methods (dispersion-kurtosis, caustics and MAMPOSSt), out to the cluster virial radius and beyond. The mass profile inferred by the strong lensing analysis in the central cluster region is slightly above, but still consistent with, the kinematics estimate. On the other hand, the X-ray based M(r) is significantly below both the kinematics and strong lensing estimates. Theoretical predictions from $Λ$CDM cosmology for the concentration--mass relation are in agreement with our observational results, when taking into account the uncertainties in both the observational and theoretical estimates. There appears to be a central deficit in the intra-cluster gas mass fraction compared to nearby clusters. Despite the relaxed appearance of this cluster, the determinations of its mass profile by different probes show substantial discrepancies, the origin of which remains to be determined. The extension of a similar dynamical analysis to other clusters of the DAFT/FADA survey will allow to shed light on the possible systematics that affect the determination of mass profiles of high-z clusters, possibly related to our incomplete understanding of intracluster baryon physics.

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arXiv2013

Structure and substructure analysis of DAFT/FADA galaxy clusters in the [0.4-0.9] redshift range

We analyse the structures of all the clusters in the DAFT/FADA survey for which XMM-Newton and/or a sufficient number of galaxy redshifts in the cluster range is available, with the aim of detecting substructures and evidence for merging events. These properties are discussed in the framework of standard cold dark matter cosmology.XMM-Newton data were available for 32 clusters, for which we derive the X-ray luminosity and a global X-ray temperature for 25 of them. For 23 clusters we were able to fit the X-ray emissivity with a beta-model and subtract it to detect substructures in the X-ray gas. A dynamical analysis based on the SG method was applied to the clusters having at least 15 spectroscopic galaxy redshifts in the cluster range: 18 X-ray clusters and 11 clusters with no X-ray data. Only major substructures will be detected. Ten substructures were detected both in X-rays and by the SG method. Most of the substructures detected both in X-rays and with the SG method are probably at their first cluster pericentre approach and are relatively recent infalls. We also find hints of a decreasing X-ray gas density profile core radius with redshift. The percentage of mass included in substructures was found to be roughly constant with redshift with values of 5-15%, in agreement both with the general CDM framework and with the results of numerical simulations. Galaxies in substructures show the same general behaviour as regular cluster galaxies; however, in substructures, there is a deficiency of both late type and old stellar population galaxies. Late type galaxies with recent bursts of star formation seem to be missing in the substructures close to the bottom of the host cluster potential well. However, our sample would need to be increased to allow a more robust analysis.

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arXiv2013

A comprehensive picture of baryons in groups and clusters of galaxies

(Abridged) Based on XMM-Newton, Chandra and SDSS data, we investigate the baryon distribution in groups and clusters and its use as a cosmological constraint. For this, we considered a sample of 123 systems, with total masses in the mass range M500 = ~ 10^13 - 4 x 10^15 h_70^-1 Msun. The gas masses and total masses are derived from X-ray data under the assumption of hydrostatic equilibrium and spherical symmetry. The stellar masses are based on SDSS-DR8 data. For the 37 systems out of 123 that had both optical and X-ray data available, we investigated the gas, stellar and total baryon mass fractions inside r2500 and r500, and the differential gas mass fraction within the spherical annulus between r2500 and r500, as a function of total mass. For the other objects, we investigated the gas mass fraction only. We find that the gas mass fraction inside r2500 and r500 depends on the total mass. However, the differential gas mass fraction does not show any dependence on total mass for systems with M500 > 10^14 Msun. We find that the total baryonic content increases with cluster mass. This led us to investigate the contribution of the ICL to the total baryon budget for lower mass systems, but we find that it cannot account for the difference observed. The gas mass fraction dependence on total mass observed for groups and clusters could be due to the difficulty of low-mass systems to retain gas inside the inner region. Due to their shallower potential well, non-thermal processes are more effective in expelling the gas from their central regions outwards. Since the differential gas mass fraction is nearly constant it provides better constraints for cosmology. Using our total f_b estimates, our results imply 0.17 < Omega_m < 0.55.

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arXiv2009

Cluster and cluster galaxy evolution history from IR to X-ray observations of the young cluster RX J1257.2+4738 at z=0.866

The cosmic time around the z~1 redshift range appears crucial in the cluster and galaxy evolution, since it is probably the epoch of the first mature galaxy clusters. Our knowledge of the properties of the galaxy populations in these clusters is limited because only a handful of z~1 clusters are presently known. In this framework, we report the discovery of a z~0.87 cluster and study its properties at various wavelengths. We gathered X-ray and optical data (imaging and spectroscopy), and near and far infrared data (imaging) in order to confirm the cluster nature of our candidate, to determine its dynamical state, and to give insight on its galaxy population evolution. Our candidate structure appears to be a massive z~0.87 dynamically young cluster with an atypically high X-ray temperature as compared to its X-ray luminosity. It exhibits a significant percentage ~90% of galaxies that are also detected in the 24micron band. The cluster RXJ1257.2+4738 appears to be still in the process of collapsing. Its relatively high temperature is probably the consequence of significant energy input into the intracluster medium besides the regular gravitational infall contribution. A significant part of its galaxies are red objects that are probably dusty with on-going star formation.

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arXiv2008

The optical/X-ray connection: ICM iron content and galaxy optical luminosity in 20 galaxy clusters

X-ray observations of galaxy clusters have shown that the intra-cluster gas has iron abundances of about one third of the solar value. These observations also show that part (if not all) of the intra-cluster gas metals were produced within the member galaxies. We present a systematic analysis of 20 galaxy clusters to explore the connection between the iron mass and the total luminosity of early-type and late-type galaxies, and of the brightest cluster galaxies (BCGs). From our results, the intra-cluster medium (ICM) iron mass seems to correlate better with the luminosity of the BCGs than with that of the red and blue galaxy populations. As the BCGs cannot produce alone the observed amount of iron, we suggest that ram-pressure plus tidal stripping act together to enhance, at the same time, the BCG luminosities and the iron mass in the ICM. Through the analysis of the iron yield, we have also estimated that SN Ia are responsible for more than 50% of the total iron in the ICM. This result corroborates the fact that ram-pressure contributes to the gas removal from galaxies to the inta-cluster medium, being very efficient for clusters in the temperature range 2 < kT (keV)< 10

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arXiv2008

Star formation efficiency in galaxy clusters

The luminous material in clusters of galaxies falls primarily into two forms: the visible galaxies and the X-ray emitting intra-cluster medium. The hot intra-cluster gas is the major observed baryonic component of clusters, about six times more massive than the stellar component. The mass contained within visible galaxies amounts to approximately 3% of the dynamical mass. Our aim was to analyze both baryonic components, combining X-ray and optical data of a sample of five galaxy clusters (Abell 496, 1689, 2050, 2631 and 2667), within the redshift range 0.03 < z < 0.3. We determined the contribution of stars in galaxies and the intra-cluster medium to the total baryon budget. We used public XMM-Newton data to determine the gas mass and to obtain the X-ray substructures. Using the optical counterparts from SDSS or CFHT we determined the stellar contribution. We examine the relative contribution of galaxies, intra-cluster light and intra-cluster medium to baryon budget in clusters through the stellar-to-gas mass ratio, estimated with use of recent data. We find that the stellar-to-gas mass ratio within r_500 (the radius which the mean cluster density exceeds the critical density by a factor of 500), is anti-correlated with the ICM temperature, ranging from 24% to 6% whereas the temperature ranges from 4.0 to 8.3 keV. This indicates that less massive cold clusters are more prolific star forming environments than massive hot clusters.

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arXiv2007

Witnessing the formation of a galaxy cluster at z=0.485: optical and X-ray properties of RX J1117.4+0743 ([VMF 98] 097)

We present a multiwavelength study of the poor cluster RX J1117.4+0743 ([VMF 98] 097) at z=0.485, based on GMOS/Gemini South g', r' photometry and spectroscopy, and XMM-Newton observations. We examine its nature and surroundings by analyzing the projected galaxy distribution, the galaxy velocity distribution, the weak-lensing mass reconstruction, and the X-ray spectroscopy and imaging. The cluster shows a complex morphology. It is composed by at least two structures along the line-of-sight, with velocity dispersions of 592+-82 km s^-1 and 391+-85 km s^-1 respectively. Other structures are also detected in X-ray, in the galaxy projected number density map, and by weak-lensing. One of these clumps, could be gravitationally bound and associated to the main cluster. The derived temperature and bolometric X-ray luminosity reveal that [VMF 98] 097 behave like a normal cluster, in agreement with Lx-Tx correlation found for both local (z=0) and moderate redshift (z~0.4) clusters. We find that the mass determination inferred from weak-lensing is in average 3 to 4.8 times higher (depending on the model assumed) than the X-ray mass. We have two possible explanations for this discrepancy: i) the cluster is in non-equilibrium, then the deviation of the X-ray estimated mass from the true value can be as high as a factor of two; ii) the intervening mass along the line-of-sight of the cluster is producing an over-estimation of the weak-lensing mass. Based on the analysis presented, we conclude that [VMF 98] 097 is a perturbed cluster with at least two substructures in velocity space and with other nearby structures at projected distances of about 1 h^-1 Mpc. This cluster is an example of a poor cluster caught in the process of accreting sub-structures to become a rich cluster.

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arXiv2006

Discovery of a cluster of galaxies behind the Milky Way: X-ray and optical observations

We report the discovery of Cl 2334+48, a rich cluster of galaxies in the Zone of Avoidance, identified in public images from the XMM-Newton archive. We present the main properties of this cluster using the XMM-Newton X-ray data, along with new optical spectroscopic and photometric observations. Cl 2334+48 is located at z = 0.271 +/- 0.001, as derived from the optical spectrum of the brightest member galaxy. Such redshift agrees with a determination from the X-ray spectrum (z = 0.263 (+0.012/-0.010)), in which an intense emission line is matched to the rest wavelength of the Fe Kalpha complex. Its intracluster medium has a plasma temperature of 4.92 (+0.50/-0.48) keV, sub-solar abundance (0.38 +/- 0.12 Zsun), and a bolometric luminosity of 3.2 x 10^44 erg/s. A density contrast delta = 2500 is obtained in a radius of 0.5 Mpc/h70, and the corresponding enclosed mass is 1.5 x 10^14 Msun. Optical images show an enhancement of g'-i' > 2.5 galaxies around the central galaxy, as expected if these were cluster members. The central object is a luminous E-type galaxy, which is displaced ~ 40 kpc/h70 from the cluster X-ray center. In addition, it has a neighbouring arc-like feature (~ 22" or 90 kpc/h70 from it), probably due to strong gravitational lensing. The discovery of Cl 2334+48 emphasises the remarkable capability of the XMM-Newton to reveal new clusters of galaxies in the Zone of Avoidance.

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arXiv2006

Diffuse light and building history of the galaxy cluster Abell 2667

We have searched for diffuse intracluster light in the galaxy cluster Abell 2667 (z=0.233) from HST images in three filters. We have applied to these images an iterative multi-scale wavelet analysis and reconstruction technique, which allows to subtract stars and galaxies from the original images. We detect a zone of diffuse emission south west of the cluster center (DS1), and a second faint object (ComDif), within DS1. Another diffuse source (DS2) may be detected, at lower confidence level, north east of the center. These sources of diffuse light contribute to 10-15% of the total visible light in the cluster. Whether they are independent entities or are part of the very elliptical external envelope of the central galaxy remains unclear. VLT VIMOS integral field spectroscopy reveals a faint continuum at the positions of DS1 and ComDif but do not allow to compute a redshift. A hierarchical substructure detection method reveals the presence of several galaxy pairs and groups defining a similar direction as the one drawn by the DS1-central galaxy-DS2 axis. The analysis of archive XMM-Newton and Chandra observations shows X-ray emission elongated in the same direction. The X-ray temperature map shows the presence of a cool core, a broad cool zone stretching from north to south and hotter regions towards the north east, south west and north west. This possibly suggests shock fronts along these directions produced by infalling material. These various data are consistent with a picture in which diffuse sources are concentrations of tidal debris and harassed matter expelled from infalling galaxies by tidal stripping and undergoing an accretion process onto the central cluster galaxy; as such, they are expected to be found along the main infall directions.

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