Search

Brightest cluster galaxies (BCGs) are very massive elliptical galaxies found at the centers of clusters. Their study gives clues on the formation and evolution of the clusters in which they are embedded. We analysed here in a homogeneous way the properties of a sample of more than one thousand BCGs in the redshift range 0.15 < z < 0.7, based on images from the Canada France Hawaii Telescope Legacy Survey. Based on the cluster catalogue of 1371 clusters by Sarron et al. (2018), we applied our automatic BCG detection algorithm and identified successfully 70% of the BCGs in our sample. We analysed their 2D photometric properties with GALFIT. We also compared the position angles of the BCG major axes with those of the overall cluster to which they belong. We found no evolution of the BCG properties with redshift up to z = 0.7, in agreement with previous results by Chu et al. (2021), who analysed an order of magnitude smaller sample, but reaching a redshift z = 1.8. The Kormendy relation for BCGs is tight and consistent with that of normal elliptical galaxies and BCGs measured by other authors. The position angles of the BCGs and of the cluster to which they belong agree within 30 degrees for 55% of the objects with well defined position angles. The study of this very large sample of more than one thousand BCGs shows that they were mainly formed before z = 0.7, as we find no significant growth for the luminosities and sizes of central galaxies. We discuss the importance of the intracluster light in the interpretation of these results. We highlight the role of image depth in the modelisation of the luminosity profiles of BCGs, and give evidence for the presence of an inner structure which can only be resolved on deep surveys with limiting apparent magnitude at 80% completeness m80 > 26 mag/arcsec2., Comment: Accepted for publication in Astronomy & Astrophysics

The pressure exerted by the ambient hot X-ray gas on cluster galaxies can lead to the presence of ram pressure stripped (RPS) galaxies, characterized by asymmetric shapes, and, in some cases, tails of blue stars and/or X-ray gas, with increased star formation. We searched for such galaxies in the cluster MS 0451.6-0305 at z~0.5, based on Hubble Space Telescope (HST) imaging covering a region of about 6x6 Mpc^2, an eight magnitude ground-based catalogue with photometric redshifts, and a spectroscopic redshift catalogue. We defined as cluster members a spectroscopic redshift sample of 359 galaxies within 4sigma_v of the mean cluster velocity, and a photometric redshift sample covering the [0.48,0.61] range. We searched for RPS galaxies and tested the error on their classification with a Zooniverse collaboration, and computed the phase space diagram for the spectroscopic sample. We ran the LePhare stellar population synthesis code to analyze and compare the properties of RPS and non-RPS galaxies. We find 56 and 273 RPS candidates in the spectroscopic and photometric redshift samples, respectively, distributed throughout the cluster and tending to avoid high density regions. The phase space diagram gives the percentages of virialized, backsplash, and infall galaxies. RPS galaxy candidates typically show rather high star formation rates, young ages, and relatively low masses. This study confirms that RPS galaxies host, on average, younger stellar populations and strongly form stars when compared with non-RPS counterparts. The fact that RPS candidates with spectroscopic and with photometric redshifts have comparable properties shows that large samples of such objects could be gathered based on multi-band photometry only, a promising result in view of future very large imaging surveys., Comment: Accepted for publication in Astronomy & Astrophysics

We observe a system of filaments and clusters around Cl0016+1609 and MACSJ1621.4+3810 using the SITELLE Fourier transform spectrograph at the Canada France Hawaii Telescope. For Cl0016+1609 (z=0.546), the observations span an 11.8 Mpc x 4.3 Mpc region along an eastern filament which covers the main cluster core, as well as two 4.3 Mpc x 4.3 Mpc regions which each cover southern subclumps. For MACSJ1621.4+3810 (z= 0.465), 3.9 Mpc x 3.9 Mpc around the main cluster core is covered. We present the frequency and location of the emission line galaxies, their emission line images, and calculate the star formation rates, specific star formation rates and merger statistics. In Cl0016+1609, we find thirteen [OII]~3727 Angstrom emitting galaxies with star formation rates between 0.2 and 14.0 M$_{\odot}$ yr$^{-1}$. 91$^{+3}_{-10}$% are found in regions with moderate local galaxy density, avoiding the dense cluster cores. These galaxies follow the main filament of the superstructure, and are mostly blue and disky, with several showing close companions and merging morphologies. In MACSJ1621.4+3810, we find ten emission line sources. All are blue (100$^{+0}_{-15}$%), with 40$^{+16}_{-12}$% classified as disky and 60$^{+12}_{-16}$% as merging systems. Eight avoid the cluster core (80$^{+7}_{-17}$%), but two (20$^{+17}_{-7}$%) are found near high density regions, including the brightest cluster galaxy (BCG). These observations push the spectroscopic study of galaxies in filaments beyond z~ 0.3 to z~ 0.5. Their efficient confirmation is paramount to their usefulness as more galaxy surveys come online., Comment: 19 pages, 12 figures, Accepted for publication in the Astronomical Journal

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 a sample of 40 clusters from the DAFT/FADA and CLASH surveys covering the redshift range 0.2

Brightest cluster galaxies (BCGs) have grown by accreting numerous smaller galaxies and can be used as tracers of cluster formation and evolution in the cosmic web. However, there is still a controversy on the main epoch of formation of BCGs, since some authors believe they have already formed before redshift z=2, while others still find them to evolve at more recent epochs. We aim to analyse the physical properties of a large sample of BCGs covering a wide redshift range up to z=1.8 and analysed in a homogeneous way, to see if their characteristics vary with redshift. As a first step, we also present a new tool to define for each cluster which galaxy is the BCG. For a sample of 137 clusters with HST images in the optical and/or infrared, we analyse the BCG properties by applying GALFIT with one or two Sersic components. For each BCG, we compute the Sersic index, effective radius, major axis position angle, surface brightness. We then search for correlations of these quantities with redshift. We find that BCGs follow the Kormendy relation (between the effective radius and the mean surface brightness), with a slope that remains constant with redshift, but with a variation with redshift of the ordinate at the origin. Although the trends are faint, we find that both the absolute magnitudes and effective radii tend to become respectively brighter and bigger with decreasing redshift. On the other hand, we find no significant correlation of the mean surface brightnesses or Sersic indices with redshift. The major axes of the cluster elongations and of the BCGs agree within 30 degrees for 73% of our clusters at redshift z <= 0.9. Our results agree with the BCGs being mainly formed before redshift z=2. The alignment of the major axes of BCGs with their clusters agree with the general idea that BCGs form at the same time as clusters by accreting matter along the filaments of the cosmic web., Comment: Accepted for publication in Astronomy & Astrophysics

We present X-ray and optical properties of the optically confirmed galaxy cluster sample from the 3XMM/SDSS Stripe 82 cluster survey. The sample includes 54 galaxy clusters in the redshift range of 0.05-1.2, with a median redshift of 0.36. We first present the X-ray temperature and luminosity measurements that are used to investigate the X-ray luminosity-temperature relation. The slope and intercept of the relation are consistent with those published in the literature. Then, we investigate the optical properties of the cluster galaxies including their morphological analysis and the galaxy luminosity functions. The morphological content of cluster galaxies is investigated as a function of cluster mass and distance from the cluster center. No strong variation of the fraction of early and late type galaxies with cluster mass is observed. The fraction of early type galaxies as a function of cluster radius varies as expected. The individual galaxy luminosity functions (GLFs) of red sequence galaxies were studied in the five ugriz bands for 48 clusters. The GLFs were then stacked in three mass bins and two redshift bins. Twenty clusters of the present sample are studied for the first time in X-rays, and all are studied for the first time in the optical range. Altogether, our sample appears to have X-ray and optical properties typical of average cluster properties., Comment: accepted for publications in MNRAS

Galaxy clusters and groups are thought to accrete material along the preferred direction of cosmic filaments. Yet these structures have proven difficult to detect due to their low contrast with few studies focusing on cluster infall regions. In this work, we detected cosmic filaments around galaxy clusters using photometric redshifts in the range 0.15

We investigate the optical properties of Ophiuchus to obtain clues on the formation epoch of this cluster, and compare them to those of the Coma cluster, which is comparable in mass to Ophiuchus but much more disturbed dynamically. Based on a deep image of the Ophiuchus cluster in the r' band obtained at the Canada France Hawaii Telescope with the MegaCam camera, we have applied an iterative process to subtract the contribution of the numerous stars that pollute the image, due to the low Galactic latitude of the cluster, and obtained a photometric catalogue of 2818 galaxies fully complete at r'=20.5 mag and still 91% complete at r'=21.5 mag. We use this catalogue to derive the cluster Galaxy Luminosity Function (GLF) for the overall image and for a region (hereafter the "rectangle" region) covering exactly the same physical size as the region in which the GLF of the Coma cluster was studied by Adami et al. (2007). We then compute density maps based on an adaptive kernel technique, for different magnitude limits, and define three circular regions covering 0.08, 0.08 and 0.06 deg^2 respectively centered on the cluster (C), northwest (NW) and southeast (SE) of the cluster, in which we compute the GLFs. The GLF fits are much better when a Gaussian is added to the usual Schechter function, to account for the excess of very bright galaxies. Compared to Coma, Ophiuchus shows a strong excess of bright galaxies. The properties of the two nearby very massive clusters Ophiuchus and Coma are quite comparable, though they seem embedded in different large scale environments. Our interpretation is that Ophiuchus has built up long ago, as confirmed by its relaxed state (see paper I) while Coma is still in the process of forming., Comment: Accepted for publication in Astronomy & Astrophysics

We present the first results of a new spectroscopic survey of the cluster Abell 85 targeting 1466 candidate cluster members within the central $\sim$1 deg$^2$ of the cluster and having magnitudes $m_r < 20.5$ using VIMOS/VLT and HYDRA/WIYN. A total of 520 galaxies are confirmed as either relaxed cluster members or part of an infalling population. A significant fraction are low mass; the median stellar mass of the sample is $10^{9.6} M_{\odot} $, and 25% have stellar masses below $10^9 M_{\odot}$ (i.e. 133 dwarf galaxies). We also identify seven active galactic nuclei (AGN), four of which reside in dwarf host galaxies. We probe the evolution of star formation rates, based on H$\alpha$ emission and continuum modeling, as a function of both mass and environment. We find that more star forming galaxies are observed at larger clustercentric distances, while infalling galaxies show evidence for recently enhanced star forming activity. Main sequence galaxies, defined by their continuum star formation rates, show different evolutionary behavior based on their mass. At the low mass end, the galaxies have had their star formation recently quenched, while more massive galaxies show no significant change. The timescales probed here favor fast quenching mechanisms, such as ram-pressure stripping. Galaxies within the green valley, defined similarly, do not show evidence of quenching. Instead, the low mass galaxies maintain their levels of star forming activity, while the more massive galaxies have experienced a recent burst., Comment: 15 pages, 10 figures, accepted for publication in MNRAS

Obtaining large samples of galaxy clusters is important for cosmology, since cluster counts as a function of redshift and mass can constrain the parameters of our Universe. They are also useful to understand the formation and evolution of clusters. We develop an improved version of the AMACFI cluster finder (now AMASCFI) and apply it to the 154 deg2 of the Canada France Hawaii Telescope Legacy Survey (CFHTLS) to obtain a catalogue of 1371 cluster candidates with mass M200 > 10^14 Msun and redshift z < 0.7. We derive the selection function of AMASCFI from the Millennium simulation, and cluster masses from a richness-mass scaling relation built from matching our candidates with X-ray detections. We study the evolution of these clusters with mass and redshift by computing the i'-band galaxy luminosity functions (GLFs) for the early (ETGs) and late-type galaxies (LTGs). This sample is 90% pure and 70% complete, therefore our results are representative the cluster population in these redshift and mass ranges. We find an increase of both the ETG and LTG faint populations with decreasing redshift (with Schechter slopes alpha_ETG = -0.65 +/- 0.03 at z=0.6 and alpha_ETG = -0.79 +\- 0.02 at z=0.2) and also a decrease of the LTG bright end, but not of the ETG's. Our large sample allows us to break the degeneracy between mass and redshift, finding that the redshift evolution is more pronounced in high-mass clusters, but that there is no significant dependence of the faint end on mass for a given redshift. These results show that the cluster red sequence is mainly formed at redshift z > 0.7, and that faint ETGs continue to enrich the red sequence through quenching of brighter LTGs at z < 0.7. The efficiency of this quenching is higher in large-mass clusters while the accretion rate of faint LTGs is lower as the more massive clusters have already emptied most of their environment at higher redshifts., Comment: 22 pages, 24 figures, matches version accepted to A&A

We present the chemical distribution of the Milky Way, based on 2,900$\, {\rm deg^2}$ of $u$-band photometry taken as part of the Canada-France Imaging Survey. When complete, this survey will cover 10,000$\, {\rm deg^2}$ of the Northern sky. By combing the CFHT $u$-band photometry together with SDSS and Pan-STARRS $g,r,$ and $i$, we demonstrate that we are able to measure reliably the metallicities of individual stars to $\sim 0.2$ dex, and hence additionally obtain good photometric distance estimates. This survey thus permits the measurement of metallicities and distances of the dominant main-sequence population out to approximately 30 kpc, and provides much higher number of stars at large extraplanar distances than have been available from previous surveys. We develop a non-parametric distance-metallicity decomposition algorithm and apply it to the sky at $30\deg < |b| < 70\deg$ and to the North Galactic Cap. We find that the metallicity-distance distribution is well-represented by three populations whose metallicity distributions do not vary significantly with vertical height above the disk. As traced in main-sequence stars, the stellar halo component shows a vertical density profile that is close to exponential, with a scale height of around 3 kpc. This may indicate that the inner halo was formed partly from disk stars ejected in an ancient minor merger., Comment: 21 pages, 17 figures, accepted for publication in ApJ

The Canada-France Imaging Survey (CFIS) will map the northern high Galactic latitude sky in the $u$-band ("CFIS-u", 10,000$\, {\rm deg^2}$) and in the $r$-band ("CFIS-r", 5,000$\, {\rm deg^2}$), enabling a host of stand-alone science investigations, and providing some of the ground-based data necessary for photometric redshift determination for the Euclid mission. In this first contribution we present the $u$-band component of the survey, describe the observational strategy, and discuss some first highlight results, based on approximately one third of the final area. We show that the Galactic anticenter structure is distributed continuously along the line of sight, out to beyond 20 kpc, and possesses a metallicity distribution that is essentially identical to that of the outer disk sampled by APOGEE. This suggests that it is probably a buckled disk of old metal-rich stars, rather than a stream or a flare. We also discuss the future potential for CFIS-u in discovering star-forming dwarf galaxies around the Local Group, the characterization of the white dwarf and blue straggler population of the Milky Way, as well as its sensitivity to low-surface brightness structures in external galaxies., Comment: 12 pages, 11 figures, accepted for publication in ApJ

Characterizing the evolution of the faint end of the cluster red sequence (RS) galaxy luminosity function (GLF) with redshift is a milestone in understanding galaxy evolution. However, the community is still divided in that respect, hesitating between an enrichment of the RS due to efficient quenching of blue galaxies from $z\sim1$ to present-day or a scenario in which the RS is built at a higher redshift and does not evolve afterwards. Recently, it has been proposed that surface brightness (SB) selection effects could possibly solve the literature disagreement, accounting for the diminishing of the RS faint population in ground based observations. We investigate this hypothesis by comparing the RS GLFs of 16 CLASH clusters computed independently from ground-based Subaru/Suprime-Cam and HST/ACS images in the redshift range $0.187\leq z\leq0.686$. We stack individual cluster GLFs in redshift and mass bins. We find similar RS GLFs for space and ground based data, with a difference of 0.2$\sigma$ in the faint end parameter $\alpha$ when stacking all clusters together and a maximum difference of 0.9$\sigma$ in the case of the high redshift stack, demonstrating a weak dependence on the type of observations in the probed range of redshift and mass. When considering the full sample, we estimate $\alpha = -0.76 \pm 0.07$ and $\alpha = -0.78 \pm 0.06$ with HST and Subaru respectively. We note a mild variation of the faint end with redshift at a 1.7$\sigma$ and 2.6$\sigma$ significance. We investigate the effect of SB dimming by simulating our low redshift galaxies at high redshift. We measure an evolution in the faint end slope of less than 1$\sigma$ in this case, implying that the observed signature is moderately larger than one would expect from SB dimming alone, and indicating a true evolution in the faint end slope. (Abridged...), Comment: Accepted for publication in A&A

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 & A3376E. Based on new deep multi-wavelength 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 these merging system. We have found the individual masses of M_{200}^{W}=3.0_{-1.7}^{+1.3}x10^{14} M_{\odot} and M_{200}^{E}=0.9_{-0.8}^{+0.5}x10^{14} M_{\odot}. 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 M_{200}^{N}=1.4_{-1.0}^{+0.7}x10^{14} M_{\odot}. 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 deg +-11 deg 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., Comment: Accepted for publication in MNRAS on Mar 28th 2017, 14 pages, 13 figures and 5 tables

We present a galaxy cluster survey based on XMM-Newton observations that are located in Stripe 82 of the Sloan Digital Sky Survey (SDSS). The survey covers an area of 11.25 deg$^2$. The X-ray cluster candidates were selected as serendipitously extended detected sources from the third XMM-Newton serendipitous source catalogue (3XMM-DR5). A cross-correlation of the candidate list that comprises 94 objects with recently published X-ray and optically selected cluster catalogues provided optical confirmations and redshift estimates for about half of the candidate sample. We present a catalogue of X-ray cluster candidates previously known in X-ray and/or optical bands from the matched catalogues or NED. The catalogue consists of 54 systems with redshift measurements in the range of 0.05-1.19 with a median of 0.36. Of these, 45 clusters have spectroscopic confirmations as stated in the matched catalogues. We spectroscopically confirmed another 6 clusters from the available spectroscopic redshifts in the SDSS-DR12. The cluster catalogue includes 17 newly X-ray discovered clusters, while the remainder were detected in previous XMM-Newton and/or ROSAT cluster surveys. Based on the available redshifts and fluxes given in the 3XMM-DR5 catalogue, we estimated the X-ray luminosities and masses for the cluster sample. We also present the list of the remaining X-ray cluster candidates (40 objects) that have no redshift information yet in the literature. Of these candidates, 25 sources are considered as distant cluster candidates beyond a redshift of 0.6. We also searched for galaxy cluster mergers in our cluster sample and found two strong candidates for newly discovered cluster mergers at redshifts of 0.11 and 0.26. The X-ray and optical properties of these systems are presented., Comment: 17 pages, 12 figures, accepted for publication in A&A, revised version after language editing

While our current cosmological model places galaxy clusters at the nodes of a filament network (the cosmic web), we still struggle to detect these filaments at high redshifts. We perform a weak lensing study for a sample of 16 massive, medium-high redshift (0.4

Clusters of galaxies are at the intersection of cosmic filaments and are still accreting galaxies and groups along these preferential directions, but, because of their relatively low contrast on the sky, they are difficult to detect (unless a large amount of spectroscopic data are available), and unambiguous detections have been limited until now to relatively low redshifts (z<0.3). We searched for extensions and filaments around the thirty clusters of the DAFT/FADA survey (redshift range 0.4

Here we highlight our recent results from the IFS study of Mrk178, the closest metal-poor WR galaxy, and of IZw18, the most metal-poor star-forming galaxy known in the local Universe. The IFS data of Mrk178 show the importance of aperture effects on the search for WR features, and the extent to which physical variations in the ISM properties can be detected. Our IFS data of IZw18 reveal its entire nebular HeII4686-emitting region, and indicate for the first time that peculiar, very hot (nearly) metal-free ionizing stars (called here PopIII-star siblings) might hold the key to the HeII-ionization in IZw18., Comment: 3 pages, 4 figures, to appear in proceedings of International Workshop on Wolf-Rayet Stars (editors W.-R. Hamann, A. Sander, and H. Todt, publisher Universitat Potsdam)

The Ophiuchus cluster, at a redshift z=0.0296, is known from X-rays to be one of the most massive nearby clusters, but due to its very low Galactic latitude its optical properties have not been investigated in detail. We discuss the optical properties of the galaxies in the Ophiuchus cluster, in particular with the aim of understanding better its dynamical properties. We have obtained deep optical imaging in several bands with various telescopes, and applied a sophisticated method to model and subtract the contributions of stars in order to measure galaxy magnitudes as accurately as possible. The colour-magnitude relations obtained show that there are hardly any blue galaxies in Ophiuchus (at least brighter than r'<=19.5), and this is confirmed by the fact that we only detect two galaxies in Halpha. We also obtained a number of spectra with ESO-FORS2, that we combined with previously available redshifts. Altogether, we have 152 galaxies with spectroscopic redshifts in the 0.02<=z<=0.04 range, and 89 galaxies with both a redshift within the cluster redshift range and a measured r' band magnitude (limited to the Megacam 1x1 deg^2 field). A complete dynamical analysis based on the galaxy redshifts available shows that the overall cluster is relaxed and has a mass of 1.1x10^15 solar masses. The Sernal-Gerbal method detects a main structure and a much smaller substructure that are not separated in projection. From its dynamical properties derived from optical data, the Ophiuchus cluster seems to be overall a relaxed structure, or at most a minor merger, though in X-rays the central region (radius ~ 150 kpc) may show evidence for merging effects., Comment: Accepted for publication in Astronomy & Astrophysics

Based on a recent photometric redshift galaxy catalogue, we have searched for galaxy clusters in the Stripe~82 region of the Sloan Digital Sky Survey by applying the Adami & MAzure Cluster FInder (AMACFI). Extensive tests were made to fine-tune the AMACFI parameters and make the cluster detection as reliable as possible. The same method was applied to the Millennium simulation to estimate our detection efficiency and the approximate masses of the detected clusters. Considering all the cluster galaxies (i.e. within a 1 Mpc radius of the cluster to which they belong and with a photoz differing by less than 0.05 from that of the cluster), we stacked clusters in various redshift bins to derive colour-magnitude diagrams and galaxy luminosity functions (GLFs). For each galaxy with absolute magnitude brighter than -19.0 in the r band, we computed the disk and spheroid components by applying SExtractor, and by stacking clusters we determined how the disk-to-spheroid flux ratio varies with cluster redshift and mass. We detected 3663 clusters in the redshift range 0.15

We compute optical galaxy luminosity functions (GLFs) in the B, V, R, and I rest-frame bands for one of the largest medium-to-high-redshift (0.4 < z < 0.9) cluster samples to date in order to probe the abundance of faint galaxies in clusters. We also study how the GLFs depend on cluster redshift, mass, and substructure, and compare the GLFs of clusters with those of the field. We separately investigate the GLFs of blue and red-sequence (RS) galaxies to understand the evolution of different cluster populations. We find that the shapes of our GLFs are similar for the B, V, R, and I bands with a drop at the red GLF faint end that is more pronounced at high-redshift: alpha(red) ~ -0.5 at 0.40 < z < 0.65 and alpha(red) > 0.1 at 0.65 < z < 0.90. The blue GLFs have a steeper faint end (alpha(blue) ~ -1.6) than the red GLFs, that appears to be independent of redshift. For the full cluster sample, blue and red GLFs intersect at M(V) = -20, M(R) = -20.5, and M(I) = -20.3. A study of how galaxy types evolve with redshift shows that late type galaxies appear to become early types between z ~ 0.9 and today. Finally, the faint ends of the red GLFs of more massive clusters appear to be richer than less massive clusters, which is more typical of the lower redshift behaviour. Our results indicate that our clusters form at redshifts higher than z = 0.9 from galaxy structures that already have an established red sequence. Late type galaxies then appear to evolve into early types, enriching the red-sequence between this redshift and today. This effect is consistent with the evolution of the faint end slope of the red-sequence and the galaxy type evolution that we find. Finally, faint galaxies accreted from the field environment at all redshifts might have replaced the blue late type galaxies that converted into early types, explaining the lack of evolution in the faint end slopes of the blue GLFs., Comment: accepted for publication in A&A

Abell 3376 is a merging cluster of galaxies at redshift z=0.046, famous mostly for its giant radio arcs, and shows an elongated and highly substructured X-ray emission, but has not been analysed in detail at optical wavelengths. We have obtained wide field images of Abell 3376 in the B band and derive the GLF applying a statistical subtraction of the background in three regions: a circle of 0.29 deg radius (1.5 Mpc) encompassing the whole cluster, and two circles centered on each of the two brightest galaxies (BCG2, northeast, coinciding with the peak of X-ray emission, and BCG1, southwest) of radii 0.15 deg (0.775 Mpc). We also compute the GLF in the zone around BCG1, which is covered by the WINGS survey in the B and V bands, by selecting cluster members in the red sequence in a (B-V) versus V diagram. Finally, we discuss the dynamical characteristics of the cluster implied by a Serna & Gerbal analysis. The GLFs are not well fit by a single Schechter function, but satisfactory fits are obtained by summing a Gaussian and a Schechter function. The GLF computed by selecting galaxies in the red sequence in the region surrounding BCG1 can also be fit by a Gaussian plus a Schechter function. An excess of galaxies in the brightest bins is detected in the BCG1 and BCG2 regions. The dynamical analysis based on the Serna & Gerbal method shows the existence of a main structure of 82 galaxies which can be subdivided into two main substructures of 25 and 6 galaxies. A smaller structure of 6 galaxies is also detected. The B band GLFs of Abell 3376 are clearly perturbed, as already found in other merging clusters. The dynamical properties are consistent with the existence of several substructures, in agreement with a previously published X-ray analysis., Comment: 11 pages, 12 figures, accepted for publication in A&A

We investigate the spatial distribution of chemical abundances in a sample of low metallicity Wolf-Rayet (WR) galaxies selected from the SDSS. We used the integral field spectroscopy technique in the optical spectral range (3700-6850 AA) with PMAS attached to the CAHA 3.5 m telescope. Our statistical analysis of the spatial distributions of O/H and N/O, as derived using the direct method or strong-line parameters consistent with it, indicates that metallicity is homogeneous in five out of the six analysed objects in scales of the order of several kpc. Only in the object WR404, a gradient of metallicity is found in the direction of the low surface brightness tail. In contrast,we found an overabundance of N/O in spatial scales of the order of hundreds of pc associated with or close to the positions of the WR stars in 4 out of the 6 galaxies. We exclude possible hydrodynamical causes, such as the metal-poor gas inflow, for this local pollution by means of the analysis of the mass-metallicity relation (MZR) and mass-nitrogen-to-oxygen relation (MNOR) for the WR galaxies catalogued in the SDSS., Comment: Accepted by "Advances in Astronomy" for the special issue "Metals in 3D: A cosmic view from the integral field spectroscopy". 19 pages, 6 figures. Bold sentences corrected

We present deep surface photometry of a volume--limited sample of 21 UM emission line galaxies in broadband optical UBVRI and near infra-red (NIR) HKs filters. The sample comprises 19 blue compact galaxies (BCGs) and two spirals. For some targets the exposure times are the deepest to date. For the BCG UM462 we observe a previously undetected second disk component beyond a surface brightness level of mu_B=26 mag arcsec^{-2}. This is a true low surface brightness component with central surface brightness mu_0=24.1 mag arcsec^{-2} and scale length h_r=1.5 kpc. All BCGs are dwarfs, with M_B>=-18, and very compact, with an average scale length of h_r~1 kpc. We separate the burst and host populations for each galaxy and compare them to stellar evolutionary models with and without nebular emission contribution. We also measure the A_{180} asymmetry in all filters and detect a shift from optical to NIR in the average asymmetry of the sample. This shift seems to be correlated with the morphological class of the BCGs. Using the color-asymmetry relation, we identify five BCGs in the sample as mergers, which is confirmed by their morphological class. Though clearly separated from normal galaxies in the concentration-asymmetry parameter space, we find that it is not possible to distinguish luminous starbursting BCGs from the merely star forming low luminosity BCGs., Comment: 48 pages, 39 figures, submitted

[Abridged] We present deep optical and near-infrared UBVRIHKs imaging data for 24 blue compact galaxies (BCGs). The sample contains luminous dwarf and intermediate-mass BCGs which are predominantly metal-poor, although a few have near-solar metallicities. We have analyzed isophotal and elliptical integration surface brightness and color profiles, extremely deep (mu_B<29 mag arcsec^{-2}) contour maps and RGB images for each galaxy in the sample. The colors are compared to different spectral evolutionary models. We detect extremely extended low surface brightness (LSB) components dominant beyond the Holmberg radius as well as optical bridges between companion galaxies at the mu_V~28th mag arcsec^{-2} isophotal level. The central surface brightness mu_0 and scale length h_r are derived from two radial ranges typically assumed to be dominated by the underlying host galaxy. We find that mu_0 and h_r of the BCGs host deviate from those of dwarf ellipticals (dE) and dwarf irregulars (dI) solely due to a strong burst contribution to the surface brightness profile almost down to the Holmberg radius. Structural parameters obtained from a fainter region, mu_B=26-28 mag arcsec^{-2}, are consistent with those of true LSB galaxies for the starbursting BCGs in our sample, and with dEs and dIs for the BCGs with less vigorous star formation., Comment: 61 pages, 45 figures, submitted

Cluster faint low surface brightness galaxies (fLSBs) are difficult to observe. Consequently, their origin, physical properties and number density are not well known. After a first search for fLSBs in the highly substructured Coma cluster, we present here a search for fLSBs in Abell 496. This cluster appears to be much more relaxed than Coma, but is embedded in a large scale filament of galaxies. Our aim is to compare the properties of fLSBs in these two very different clusters, to search for environmental effects. Based on deep CFHT/Megacam images in the u*, g', r' and i' bands, we selected galaxies with r'>21 and surface brightness > 24 mag/arcsec-2. We estimated photometric redshifts for all these galaxies and kept the 142 fLSBs with photo-z<0.2. In a g'-i' versus i' color-magnitude diagram, we find that a large part of these fLSBs follow the red sequence (RS) of brighter galaxies. The fLSBs within +-1sigma of the RS show a homogeneous spatial distribution, while those above the RS appear to be concentrated along the large scale filament of galaxies. These properties are interpreted as agreeing with the idea that RS fLSBs are formed in groups prior to cluster assembly. The formation of red fLSBs could be related to infalling galaxies., Comment: Accepted for publication in A&A

The Abell 1763 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 24{\mu}m emission is much higher within the filament than at either the center of the rich galaxy cluster, or the field surrounding the system. New VLA 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 (AGN) and starbursts. 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 AGN. We find very few MIPS-selected galaxies that are clearly dominated by AGN activity. Most radio selected members within the filament are starbursts. Within the supercluster, 3 of 8 spectroscopic members detected both in the radio and in the mid-infrared are radio-bright AGN. They are found at or near the core of Abell 1763. The five starbursts 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 (BCG) of Abell 1763. 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 (ICM) 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., Comment: 26 pages, 13 figures AJ, accepted

Compact elliptical galaxies are characterized by small sizes and high stellar densities. They are thought to form through tidal stripping of massive progenitors. However, only a handful of them were known, preventing us from understanding the role played by this mechanism in galaxy evolution. We present a population of 21 compact elliptical galaxies gathered with the Virtual Observatory. Follow-up spectroscopy and data mining, using high-resolution images and large databases, show that all the galaxies exhibit old metal-rich stellar populations different from those of dwarf elliptical galaxies of similar masses but similar to those of more massive early-type galaxies, supporting the tidal stripping scenario. Their internal properties are reproduced by numerical simulations, which result in compact dynamically hot remnants resembling the galaxies in our sample., Comment: 26 pages, 5 figures, 2 tables. Science in press, published in Science Express on 1/Oct/2009. Full resolution figures in the supplementary online material are available from the Science Magazine web-site

Due to observational constraints, dark matter determinations in nearby clusters based on weak lensing are still extremely rare, in spite of their importance for the determination of cluster properties independent of other methods. We present a weak lensing study of the Coma cluster (redshift 0.024) based on deep images obtained at the CFHT. After obtaining photometric redshifts for the galaxies in our field based on deep images in the u (1x1 deg2), and in the B, V, R and I bands (42'x52'), allowing us to eliminate foreground galaxies, we apply weak lensing calculations on shape measurements performed in the u image. We derive a map of the mass distribution in Coma, as well as the radial shear profile, and the mass and concentration parameter at various radii. We obtain M_200c = 5.1+4.3-2.1 x10^14 Msun and c_200c=5.0+3.2-2.5, in good agreement with previous measurements. With deep wide field images it is now possible to analyze nearby clusters with weak lensing techniques, thus opening a broad new field of investigation.

The morphology and stellar populations of low-luminosity early-type galaxies in clusters have until now been limited to a few relatively nearby clusters such as Virgo or Fornax. Scenarii for the formation and evolution of dwarf galaxies in clusters are therefore not well constrained. We investigate here the morphology and stellar populations of low-luminosity galaxies in the relaxed cluster Abell 496 (z=0.0330). Deep multiband imaging obtained with the CFHT Megacam allowed us to select a sample of faint galaxies (-18.8

We report the first direct detection with Spitzer of galaxy filaments. Using Spitzer and ancillary optical data, we have discovered two filamentary structures in the outskirts of the cluster Abell 1763. Both filaments point toward Abell 1770 which lies at the same redshift as Abell 1763 (z=0.23), at a projected distance of ~13 Mpc. The X-ray cluster emission is elongated along the same direction. Most of the far-infrared emission is powered by star formation. According to the optical spectra, only one of the cluster members is classified as an active galactic nucleus. Star formation is clearly enhanced in galaxies along the filaments: the fraction of starburst galaxies in the filaments is more than twice than that in other cluster regions. We speculate that these filaments are feeding the cluster Abell 1763 by the infall of galaxies and galaxy groups. Evidence for one of these groups is provided by the analysis of galaxy kinematics in the central cluster region., Comment: 5 pages, 2 figures, 1 table, accepted for publication on ApJ Letters

The existence of dark matter can be proved in an astrophysical context by the discovery of a system in which the observed baryons and the inferred dark matter are spatially segregated, such as the bullet cluster (1E0657-558). The full descriptions of the dark matter halo and X-ray gas substructure motions are necessary to forecast the location of the dark halo from X-ray maps, which can be confirmed by the detection of a galaxy concentration or by gravitational lensing. We present an analytical hydrodynamic model to determine the distance between the X-ray and dark-matter components and the Mach number of the merger shock. An approximate solution is given for the problem of the substructure propagation in merging clusters. A new method to predict the position of a dark matter halo in clusters, where there is a separation between the X-ray gas and the dark halo, is proposed and applied to the clusters 1E0657-558 and Abell 1763., Comment: Accepted for publication in Astronomy & Astrophysics

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., Comment: 4 pages, 2 figs. Accepted for publication in the Proceedings of the 36th COSPAR Scientific Assembly

Aims: ``Compact ellipticals'' are so rare that a search for M32 analogs is needed to ensure the very existence of this class. Methods: We report here the discovery of A496cE, a M32 twin in the cluster Abell 496, located in the halo of the central cD. Results: Based on CFHT and HST imaging we show that the light profile of A496cE requires a two component fit: a Sersic bulge and an exponential disc. The spectrum of A496cE obtained with the ESO-VLT FLAMES/Giraffe spectrograph can be fit by a stellar synthesis spectrum dominated by old stars, with high values of [Mg/Fe] and velocity dispersion. Conclusions: The capture of A496cE by the cD galaxy and tidal stripping of most of its disc are briefly discussed., Comment: 4 pages, 4 figures, accepted for publication in A&A Letters

In the current paradigm of cold dark matter cosmology, large-scale structures are assembling through hierarchical clustering of matter. In this process, an important role is played by megaparsec (Mpc)-scale cosmic shock waves, arising in gravity-driven supersonic flows of intergalactic matter onto dark matter-dominated collapsing structures such as pancakes, filaments, and clusters of galaxies. Here, we report Very Large Array telescope observations of giant (~2 Mpc by 1.6 Mpc), ring-shaped nonthermal radio-emitting structures, found at the outskirts of the rich cluster of galaxies Abell 3376. These structures may trace the elusive shock waves of cosmological large-scale matter flows, which are energetic enough to power them. These radio sources may also be the acceleration sites where magnetic shocks are possibly boosting cosmic-ray particles with energies of up to 10^18 to 10^19 electron volts., Comment: Published on Science, 3 November 2006. Main paper and Supporting Online Material

We describe multiwavelength optical, X-ray and radio evidences of energetic mergers in southern galaxy cluster Abell 3376 (A3376, redshift z=0.046, X-ray luminosity $ \rm L_{X}(0.1-2.4 keV)= 2.48 \times 10^{44} erg s^{-1}$). Here we report the rare discovery of gigantic, Mpc-scale non-thermal radio structures (`radio-arcs'), shaped like a pair of bow-shock fronts on the merger axis. We argue for the shock acceleration origin of the radio emission and discuss the possibilty of acceleration of very high energy cosmic ray particles in this and similar clusters. At redshift z=0.04, cluster A3376 is near enough that some of these primary or secondary cosmic ray components could actually be detected by new cosmic ray telescopes, particularly the energetic inverse Compton hard X-ray/gamma-ray photons upto extreme energies $E_{\gamma} \sim 100 {\gamma^{e}_{7}}^{2}$ GeV (where ${\gamma^{e}_{7}}$ is the electron Lorentz factor in units of $10^7$). Identification of radio or hard X-ray/gamma-ray emission from structure formation shocks holds a great promise for advancing current knowledge on shock formation in the IGM. It should provide the first direct evidence for such shocks, revealing the underlying large-scale cosmological flows. When combined with hard X-ray or gamma-ray detection, the radio signal will provide a direct measure of the unknown magnetic fields in the IGM, thus providing a better understanding of processes leading to IGM magnetization and also acceleration and propagation of ultra-high energy cosmic rays., Comment: Replaced with slightly modified submitted version. We discuss the possiblity of both accretion-skocks and merger-shocks. 4 pages, 2 Figures. To appear in the Proceedings of the 29th International Cosmic Ray Conference (ICRC), Pune, India

Our XMM-Newton observations of Abell 85 confirm the extended 4 Mpc filament first detected with ROSAT, which has an X-ray temperature of about 2 keV and is probably made of groups falling on to the cluster. A comparison of the temperature map with numerical simulations show that Abell 85 had intense merging activity in the past and is not fully relaxed, even in the central region. Finally, a deprojected temperature profile has been calculated and used, together with the suface brightness, to estimate the entropy and pressure profiles. Abell 85 only presents a mild flattening of the entropy profile in the center, showing no evidence of an ``entropy floor''., Comment: Contribution to the Proceedings of the COSPAR Scientific Assembly, E1.2 "Clusters of Galaxies: New Insights from XMM-Newton, Chandra and INTEGRAL", Paris (France), July 19-20, 2004, accepted for publication in Advances in Space Research

From ROSAT data, the bright X-ray cluster Abell 85 was found to show a roughly symmetrical shape, on to which are superimposed several features, among which: (1) a blob or group of galaxies falling on to the main cluster, with the gas in the impact region probably hotter and the galaxies in that zone showing enhanced star formation; (2) a filament, either diffuse or made of small groups of galaxies, extending at least 4 Mpc from the cluster (Durret et al. 1998). Preliminary results obtained from XMM-Newton and Chandra observations of Abell 85 and its filament will be presented., Comment: Poster paper presented at the conference ``Matter and Energy in Clusters of Galaxies'', Taiwan April 23-27, 2002, Chorng-Yuan Hwang and Stuart Bowyer, Eds

We have derived the galaxy luminosity function (GLF) in the cluster of galaxies Abell 496 from a wide field image in the I band. A single Schechter function reproduces quite well the GLF in the 17 <= I_{AB} <= 22 (-19.5 <= M_I <= -14.5) magnitude interval, and the power law index of this function is found to be somewhat steeper in the outer regions than in the inner regions. This result agrees with the idea that faint galaxies are more abundant in the outer regions of clusters, while in the denser inner regions they have partly been accreted by larger galaxies or have been dimmed or even disrupted by tidal interactions., Comment: Accepted for publication in Astronomy & Astrophysics, final version

Evidence for excess extreme ultraviolet (EUV) emission over a tail of X-ray gas bremsstrahlung emission has been building up recently, but in some cases remains controversial, mostly due to the moderate quality of the EUV data. In order to improve the signal to noise ratio in the EUV, we have performed the wavelet analysis and image reconstructions for five clusters of galaxies observed both at EUV and X-ray energies with the EUVE and ROSAT satellites respectively. The profiles of the EUV and X-ray reconstructed images all differ at a very large confidence level and an EUV excess over a thermal bremsstrahlung tail is detected in all five clusters (Abell 1795, Abell 2199, Abell 4059, Coma and Virgo) up to large radii. These results, coupled with recent XMM-Newton observations, suggest that the EUV excess is probably non thermal in origin., Comment: accepted for publication in Astronomy & Astrophysics, final version

Self-gravitating systems such as elliptical galaxies appear to have a constant specific entropy and obey a scaling law relating their potential energy to their mass. These properties can be interpreted as due to the physical processes involved in the formation of these structures. Dark matter haloes obtained through numerical simulations have also been found to obey a scaling law relating their potential energy to their mass with the same slope as ellipticals. Since the X-ray gas in clusters is weakly dissipative, we have checked the hypothesis that it might verify similar properties. We have analyzed ROSAT-PSPC images of 24 clusters, and also found that: 1) the S\'ersic law parameters (intensity, shape and scale) describing the X-ray gas emission are correlated two by two; 2) the hot gas in all these clusters roughly has the same specific entropy; 3) a scaling law linking the cluster potential energy to the mass of the X-ray gas is observed, with the same slope as for elliptical galaxies and dark matter haloes., Comment: To appear in the Proceedings of `Galaxy Clusters and the High Redshift Universe Observed in X-rays', XXIth Moriond Astrophysics Meeting (March 2001), Eds. Doris Neumann et al

A study is presented of the central structure and kinematics of the galaxy NGC 6951, by means of broad band B'IJK images and high resolution high dispersion longslit spectroscopy, together with archival HST WFPC2 V and NICMOS2 J and H images. We find that there is evidence of two modes of star formation, in bursts and continuously. The equivalent width of the CaII triplet absorption lines show that, in the metal rich central region, the continuum is dominated by a population of red supergiants. The gaseous and stellar kinematics along three slit position angles, suggest the existence of a hierarchy of disks within disks, whose dynamics are decoupled at the two ILRs, that we find at 180 pc and at 1100 pc. This is supported by the structure seen in the high resolution HST images. The nucleus is spatially resolved within a radius of 1.5 arcsec, just inside the innermost ILR. Outside the iILR, the stellar CaT velocity profile is resolved into two components, associated with the bar and the disk. Several results indicate that this is a dynamically old system. It is thus possible that a nuclear bar has existed in NGC 6951 that drove the gas towards the nucleus, as in the bars within bars scenario, but that this bar has already dissolved by the gas accumulated within the circumnuclear region. We discuss the possibility that the kinematical component inside the iILR could be due to a nuclear outflow produced by the combined effects of SN and SN remnants, or to a nuclear disk, as in the disk within disk scenario that we propose for the fueling of the AGN in NGC 6951., Comment: 14 pages, 16 figures. Accepted for publication in Astronomy and Astrophysics. High resolution images in http://www.iaa.es/~eperez/research/degas.html

We present two catalogues of galaxies in the direction of the rich cluster Abell 496. The first one includes 3,879 galaxies located in a region of roughly 1.3 degrees from the cluster centre. It has been obtained from a list of more than 35,000 galaxy candidates detected by scanning part of a Schmidt photographic plate taken in the b_J band. Positions are very accurate in this catalogue but magnitudes are not. This led us to perform CCD imaging observations in the V and R bands to calibrate these photographic magnitudes. A second catalogue gives a list of galaxies with CCD magnitudes in the V (239 galaxies) and R (610 galaxies) bands for a much smaller region in the centre of the cluster. These two catalogues will be combined with a redshift catalogue of 466 galaxies (Durret et al. 1999) to investigate the cluster properties at optical wavelengths (Durret et al. in preparation), as a complement to previous X-ray studies by a member of our group (Pislar 1998)., Comment: Accepted for publication in Astronomy & Astrophysics, Supplement Series

We present a catalogue of velocities for 466 galaxies in the direction of the cluster Abell 496, in a region covering about 160' x 160' (9.2 x 9.2 Mpc for an average redshift for Abell 496 of 0.0331, assuming H$_0$=50 km s$^{-1}$ Mpc$^{-1}$). This catalogue includes previously published redshifts by Proust et al. (1987), Quintana and Ramirez (1990) and Malumuth et al. (1992), redshifts from the CfA redshift survey, together with our new measurements. A total of 274 galaxies have velocities in the 7800-11800 km/s interval, and will be considered as members of the cluster. Abell 496 therefore becomes one of the few clusters with a high number of measured redshifts; its physical properties are investigated in a companion paper., Comment: Accepted for publication in Astronomy & Astrophysics, Supplement Series

(Abridged) We present a morphological and structural analysis of the Richness zero cluster ABCG 194, known as a ``linear cluster'', based on a catalogue of 97 galaxies with B magnitudes and redshifts, a ROSAT PSPC image and radio data. The overall large scale structure is rather smooth and comparable at optical and X-ray wavelengths. The cluster is elongated along PA $\approx 50$; however it appears as ``linear'' when taking into account only galaxies in the very central part (the axial ratio varies from 0.2 in the central region to 0.8 for a larger region). We have obtained the galaxy and X-ray emitting gas density profiles and estimated the X-ray gas and dynamical masses. At smaller scales, the analysis of both positions and velocities reveals the existence of several groups; a main structure with a nearly gaussian velocity distribution is exhibited. The velocity dispersion is small ($\sigma_{los} $ = 360 \kms). A wavelet analysis of the X-ray image reveals no large scale substructures. Small scale X-ray sources are detected, mainly corresponding to individual galaxies. ABCG 194 is overall a poor and cold relaxed cluster. We compare how its characteristics fit into various correlations found in the literature, but generally for richer/hotter clusters., Comment: Accepted for publication in Astronomy & Astrophysics

Several authors (S. Bowyer, T. Berghoeffer, and E. Korpela, hereinafter abbreviated as BBK) recently announced that the luminous extended EUV radiation from the clusters Abell 1795 and Abell 2199, which represents the large scale presence of a new and very soft emission component, is an illusion in the EUVE Deep Survey (DS) detector image. Specifically BBK found that the radial profile of photon background surface brightness, for concentric annuli centered at a detector position which has been used to observe cluster targets, shows an intrinsic `hump' of excess at small radii which resembles the detection of extended cluster EUV. We accordingly profiled background data, but found no evidence of significant central excess. However, to avoid argument concerning possible variability in the background pattern, we performed a clincher test which demonstrates that a cluster's EUV profile is invariant with respect to photon background. The test involves re-observation of A2199 and A1795 when the photon background was respectively three and two times higher than before, and using a different part of the detector. The radial profiles of both clusters, which have entirely different shapes, were accurately reproduced. In this way the BBK scenario is quantitatively excluded, with the inevitable conclusion that the detected signals are genuinely celestial., Comment: 9 pages, 7 figures