Search

Galaxies in clusters undergo several phenomena such as ram pressure stripping and tidal interactions, that can trigger or quench their star formation and, in some cases, lead to galaxies acquiring unusual shapes and long tails. We searched for jellyfish galaxy candidates in HST images of 40 clusters from the DAFT/FADA and CLASH surveys covering the redshift range 0.2

We used optical imaging and spectroscopic data to derive substructure estimates for local Universe (z < 0.11) galaxy clusters from two different samples. The first was selected through the Sunyaev–Zel’dovich (SZ) effect by the Planck satellite, and the second is an X-ray-selected sample. In agreement to X-ray substructure estimates, we found that the SZ systems have a larger fraction of substructure than the X-ray clusters. We have also found evidence that the higher mass regime of the SZ clusters, compared to the X-ray sample, explains the larger fraction of disturbed objects in the Planck data. Although we detect a redshift evolution in the substructure fraction, it is not sufficient to explain the different results between the higher-z SZ sample and the X-ray one. We have also verified a good agreement (∼ 60 per cent) between the optical and X-ray substructure estimates. However, the best level of agreement is given by the substructure classification given by measures based on the brightest cluster galaxy (BCG), either the BCG−X-ray centroid offset, or the magnitude gap between the first and second BCGs. We advocate the use of those two parameters as the most reliable and cheap way to assess cluster dynamical state. We recommend an offset cut-off ∼0.01 × R500 to separate relaxed and disturbed clusters. Regarding the magnitude gap, the separation can be done at m12 = 1.0. The central galaxy paradigm (CGP) may not be valid for ∼ 20 per cent of relaxed massive clusters. This fraction increases to ∼ 60 per cent for disturbed systems.

Poster presented at the conference Galaxy evolution Across Time, 12-16 June, Paris, France There is some disagreement in the literature concerning the evolution with redshift of the galaxy luminosity function (GLF) in galaxy clusters. Indeed, it is still unclear whether the red sequence (RS) is enriched by efficient quenching of blue late-type galaxies inside the cluster from z of about 1, or if this RS is built at higher redshift. Solving this contradiction is important to understand the physical processes driving the quenching of galaxies. However, the study of the GLF evolution has been limited to small samples and these different conclusions could be due to cluster to cluster variations. To explore this possibility, we applied our new version of the Adami and MAzure Cluster FInder (AMACFI) to the Canada France Hawaii Telescope Legacy Survey (CFHTLS) W1 field. We thus built a catalogue of thousands of cluster candidates up to z of about 1. We present the selection function of our detection algorithm. We study the evolution of the galaxy luminosity function of galaxy clusters with both redshift and cluster mass, and show preliminary results. Taking advantage of our large sample of clusters, we shall be able to break the degeneracy between redshift and mass dependence in the near future.

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 MW 200 = 3.0+1.3 −1.7 × 1014 M and ME 200 = 0.9+0.5 −0.8 × 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 MN 200 = 1.4+0.7 −1.0 × 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+0.2 −0.3 Gyr after the pericentric passage and it is currently going to the point of maximum separation between the subclusters.

The A1763 superstructure at z = 0.23 contains the first galaxy filament to be directly detected using mid-infrared observations. Our previous work has shown that the frequency of starbursting galaxies, as characterized by 24μm emission is much higher within the filament than at either the center of the rich galaxy cluster, or the field surrounding the system. New Very Large Array and XMM-Newton data are presented here. We use the radio and X-ray data to examine the fraction and location of active galaxies, both active galactic nuclei (AGNs) and starbursts (SBs). The radio far-infrared correlation, X-ray point source location, IRAC colors, and quasar positions are all used to gain an understanding of the presence of dominant AGNs. We find very few MIPS-selected galaxies that are clearly dominated by AGN activity. Most radio-selected members within the filament are SBs. Within the supercluster, three of eight spectroscopic members detected both in the radio and in the mid-infrared are radio-bright AGNs. They are found at or near the core of A1763. The five SBs are located further along the filament. We calculate the physical properties of the known wide angle tail (WAT) source which is the brightest cluster galaxy of A1763. A second double lobe source is found along the filament well outside of the virial radius of either cluster. The velocity offset of the WAT from the X-ray centroid and the bend of the WAT in the intracluster medium are both consistent with ram pressure stripping, indicative of streaming motions along the direction of the filament. We consider this as further evidence of the cluster-feeding nature of the galaxy filament.

International audience; We report on a search of a 42' by 55' area centered on the Coma cluster for low surface brightness galaxies (LSBs). We analyzed deep BVR and I- band CCD imaging using the CFH12k camera. We found over 400 LSBs. The total R magnitudes range from 22 to 26 with central surface brightness as low as 29 R mag per square arcsecond. We present the results of comparing the projected LSB distribution with the projected distributions of normal galaxies, the X-ray emission and the temperature distribution. The color magnitude relation and luminosity function will also be presented.

We have analyzed XMM-Newton archive data for five clusters of galaxies (redshifts 0.223 to 0.313) covering a wide range of dynamical states, from relaxed objects to clusters undergoing several mergers. We present here temperature maps of the X-ray gas together with a preliminary interpretation of the formation history of these clusters., 4 pages, 2 figs. Accepted for publication in the Proceedings of the 36th COSPAR Scientific Assembly

Galaxy clusters are the largest gravitationally bound structures of the Universe. At the center of these clusters generally reside the most massive galaxies observable today. These galaxies are refered to as Brightest Cluster Galaxies (BCGs), and are the final products of 10 Gyrs of consecutive galactic mergers in the densest regions of the cosmic web. In this thesis, we focus our attention on these very peculiar objects, excellent tracers of cluster formation, and ideal to study the impact of environmental processes on galactic formation. The characterization of the physical properties of BCGs is important to obtain better knowledge of these galaxies. Previous studies have found contradicting results concerning their growth: while some studies find that they are still evolving today, others find that they may have stopped growing a long time ago. In order to put things in perspective, I present here new catalogues of BCGs which have allowed me to conduct a deeper analysis of the formation of BCGs, thanks to the bigger statistics we reached. My work on the characterization of the physical properties of BCGs has shown a lack of evo- lution of their sizes and luminosities in the last 10 Gyrs, hinting at an earlier formation epoch and absence of recent significant growth. However, their structures may have changed over time, as hinted by the observation of a second component at recent epoch. This may only be due to observational biases, but deeper surveys such as the ones expected from the Euclid or the Ru- bin Observatory’s Legacy Survey of Space and Time (LSST) missions should enable us to confirm this. BCGs, because of their central locations, are more likely to undergo mergers in their lifetimes, which leave marks on their shapes. As a result, we confirm the special bond between BCGs and their host clusters as inferred from their alignments. I also offer new tools for automatic detections of BCGs on optical images. These may be ap- plied to large surveys with the use of already existing or future catalogues of clusters. In this manuscript, I also tackle the subject of fossil groups (FGs). We increase the number of known FGs and are carrying on observations in order to confirm the fossil nature of candidate FGs. We find that Brightest Group Galaxies (BGGs) of FGs show an evolution which may be more similar to that of BCGs of clusters than that of BGGs of non-FGs, as inferred from the Kormendy relation. However, the stellar evolution of FGs and non-FGs may still be comparable. Zooming in the central regions of BCGs, we look at the supermassive black holes (SMBHs) harbored at the center of clusters. From the Illustris TNG-300 cosmological simulation and using orbital integration methods, we show that radial mergers of galaxies can kick away the black hole from its central position to distances of a few parsecs to hundreds of kiloparsecs. I discuss the consequences of such an offset on the growth of SMBHs and the impact on the dynamics reigning in the central regions of BCGs and clusters. The observations and modeling of these large samples of BCGs and BGGs have given us in- sight on the formation and evolution of clusters and groups at various scales, from that of a large cluster down to the central supermassive black hole. Future instruments and surveys such as Eu- clid or LSST will provide us with samples of tens of thousands of clusters, and the tools developed ii here should be useful to analyse such large samples, to derive with a better precision the epoch of formation of clusters and groups.