arXiv subjects

Florence Durret

Publications and source records attributed to Florence Durret.

At least 37 records · Page 2Linked to original sources

arXiv2016

Weak lensing study of 16 DAFT/FADA clusters: substructures and filaments

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<z<0.9) galaxy clusters from the DAFT/FADA survey, that are imaged in at least three optical bands with Subaru/Suprime-Cam or CFHT/MegaCam. We estimate the cluster masses using an NFW fit to the shear profile measured in a KSB-like method, adding our contribution to the calibration of the observable-mass relation required for cluster abundance cosmological studies. We compute convergence maps and select structures within, securing their detection with noise re-sampling techniques. Taking advantage of the large field of view of our data, we study cluster environment, adding information from galaxy density maps at the cluster redshift and from X-ray images when available. We find that clusters show a large variety of weak lensing maps at large scales and that they may all be embedded in filamentary structures at megaparsec scale. We classify them in three categories according to the smoothness of their weak lensing contours and to the amount of substructures: relaxed (~7%), past mergers (~21.5%), recent or present mergers (~71.5%). The fraction of clusters undergoing merging events observationally supports the hierarchical scenario of cluster growth, and implies that massive clusters are strongly evolving at the studied redshifts. Finally, we report the detection of unusually elongated structures in CLJ0152, MACSJ0454, MACSJ0717, A851, BMW1226, MACSJ1621, and MS1621.

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arXiv2016

Searching for filaments and large-scale structure around DAFT/FADA clusters

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<z<0.9) with deep wide field photometric data. For each cluster, based on a colour-magnitude diagram, we selected galaxies that were likely to belong to the red sequence, and hence to be at the cluster redshift, and built density maps. By computing the background for each map and drawing 3sigma contours, we estimated the elongations of the structures detected in this way. Whenever possible, we identified the other structures detected on the density maps with clusters listed in NED. We found clear elongations in twelve clusters, with sizes reaching up to 7.6 Mpc. Eleven other clusters have neighbouring structures, but the zones linking them are not detected in the density maps at a 3sigma level. Three clusters show no extended structure and no neighbours, and four clusters are of too low contrast to be clearly visible on our density maps. The simple method we have applied appears to work well to show the existence of filaments and/or extensions around a number of clusters in the redshift range 0.4<z<0.9. We plan to apply it to other large cluster samples such as the clusters detected in the CFHTLS and SDSS-Stripe 82 surveys in the near future.

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arXiv2015

PopIII-star siblings in IZw18 and WRs in metal-poor galaxies unveiled from integral field spectroscopy

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.

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arXiv2015

Ophiuchus: an optical view of a very massive cluster of galaxies hidden behind the Milky Way

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.

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arXiv2015

Galaxy clusters in the SDSS Stripe 82 based on galaxy photometric redshifts

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<z<0.70, with estimated mean masses between 10^13 and a few 10^{14 solar masses. By stacking the cluster galaxies in various redshift bins, we find a clear red sequence in the (g'-r') versus r' colour-magnitude diagrams, and the GLFs are typical of clusters, though with a possible contamination from field galaxies. The morphological analysis of the cluster galaxies shows that the fraction of late-type to early-type galaxies shows an increase with redshift (particularly in high mass clusters) and a decrease with detection level, i.e. cluster mass. From the properties of the cluster galaxies, the majority of the candidate clusters detected here seem to be real clusters with typical cluster properties.

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arXiv2014

The evolution of the cluster optical galaxy luminosity function between z=0.4 and 0.9 in the DAFT/FADA survey

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.

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arXiv2013

The merging cluster of galaxies Abell 3376: an optical view

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.

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arXiv2013

Are Wolf-Rayet stars able to pollute the interstellar medium of galaxies? Results from the integral field spectroscopy

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.

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arXiv2012

Deep multiband surface photometry on star forming galaxies: II. A volume limited sample of 21 emission lines galaxies

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.

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arXiv2012

Deep multiband surface photometry on star forming galaxies: I. A sample of 24 blue compact galaxies

[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.

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arXiv2011

A search for faint low surface brightness galaxies in the relaxed cluster Abell 496

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.

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arXiv2010

Spitzer observations of Abell 1763 - II: Constraining the nature of activity in the cluster-feeding filament with VLA and XMM-Newton data

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 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 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.

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arXiv2009

A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory

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.

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arXiv2009

A weak lensing study of the Coma cluster

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.

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arXiv2008

Kinematics and Stellar Populations of Low-Luminosity Early-Type Galaxies in the Abell 496 Cluster

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<M_B<-15.1 mag). We observed 118 galaxies spectroscopically with the ESO VLT FLAMES/Giraffe spectrograph (R=6300). We present structural analysis and colour maps for the 48 galaxies belonging to the cluster. We fit the spectra of 46 objects with PEGASE.HR synthetic spectra to estimate the ages, metallicities, and velocity dispersions. We computed values of $α$/Fe abundance ratios from the measurements of Lick indices. High-precision estimates of stellar population properties have been obtained for a large sample of faint galaxies in a cluster, allowing for the extension of relations between stellar populations and internal kinematics to the low-velocity dispersion regime. We have revealed a peculiar population of elliptical galaxies in the core of the cluster, resembling massive early-type galaxies by their stellar population properties and velocity dispersions, but having luminosities of about 2 mag fainter. External mechanisms of gas removal (ram pressure stripping and gravitational harassment) are more likely to have occurred than internal mechanisms such as supernova-driven winds. The violent tidal stripping of intermediate-luminosity, early-type galaxies in the cluster core can explain the properties of the peculiar elliptical galaxies surrounding the cD galaxy.

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arXiv2007

Starburst galaxies in cluster-feeding filaments unveiled by Spitzer

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.

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arXiv2007

An approximate theory for substructure propagation in clusters

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.

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arXiv2007

XMM-Newton temperature maps for five intermediate redshift clusters of galaxies

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.

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