arXiv subjects

E. Slezak

Publications and source records attributed to E. Slezak.

At least 37 records · Page 2Linked to original sources

arXiv2010

The DAFT/FADA survey. I.Photometric redshifts along lines of sight to clusters in the z=[0.4,0.9] interval

As a contribution to the understanding of the dark energy concept, the Dark energy American French Team (DAFT, in French FADA) has started a large project to characterize statistically high redshift galaxy clusters, infer cosmological constraints from Weak Lensing Tomography, and understand biases relevant for constraining dark energy and cluster physics in future cluster and cosmological experiments. The purpose of this paper is to establish the basis of reference for the photo-z determination used in all our subsequent papers, including weak lensing tomography studies. This project is based on a sample of 91 high redshift (z>0.4), massive clusters with existing HST imaging, for which we are presently performing complementary multi-wavelength imaging. This allows us in particular to estimate spectral types and determine accurate photometric redshifts for galaxies along the lines of sight to the first ten clusters for which all the required data are available down to a limit of I_AB=24/24.5 with the LePhare software. The accuracy in redshift is of the order of 0.05 for the range 0.2<z<1.5. We verified that the technique applied to obtain photometric redshifts works well by comparing our results to with previous works. In clusters, photoz accuracy is degraded for bright absolute magnitudes and for the latest and earliest type galaxies. The photoz accuracy also only slightly varies as a function of the spectral type for field galaxies. As a consequence, we find evidence for an environmental dependence of the photoz accuracy, interpreted as the standard used Spectral Energy Distributions being not very well suited to cluster galaxies. Finally, we modeled the LCDCS 0504 mass with the strong arcs detected along this line of sight.

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arXiv2009

Galaxy cluster searches by photometric redshifts in the CFHTLS

In order to enlarge publicly available optical cluster catalogs, in particular at high redshift, we have performed a systematic search for clusters of galaxies in the CFHTLS. We used the Le Phare photometric redshifts for the galaxies detected with magnitude limits of i'=25 and 23 for the Deep and Wide fields respectively. We then constructed galaxy density maps in photometric redshift bins of 0.1 based on an adaptive kernel technique and detected structures with SExtractor. In order to assess the validity of our cluster detection rates, we applied a similar procedure to galaxies in Millennium simulations. We measured the correlation function of our cluster candidates. We analyzed large scale properties and substructures by applying a minimal spanning tree algorithm both to our data and to the Millennium simulations. We have detected 1200 candidate clusters with various masses (minimal masses between 1.0 10$^{13}$ and 5.5 10$^{13}$ and mean masses between 1.3 10$^{14}$ and 12.6 10$^{14}$ M$_\odot$), thus notably increasing the number of known high redshift cluster candidates. We found a correlation function for these objects comparable to that obtained for high redshift cluster surveys. We also show that the CFHTLS deep survey is able to trace the large scale structure of the universe up to z$\geq$1. Our detections are fully consistent with those made in various CFHTLS analyses with other methods. We now need accurate mass determinations of these structures to constrain cosmological parameters.

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arXiv2009

The cluster Abell 780: an optical view

The Abell 780 cluster, better known as the Hydra A cluster, has been thouroughly analyzed in X-rays. However, little is known on its optical properties. We derive the galaxy luminosity function (GLF) in this apparently relaxed cluster, and search for possible environmental effects by comparing the GLFs in various regions, and by looking at the galaxy distribution at large scale around Abell 780. Our study is based on optical images obtained with the ESO 2.2m telescope and WFI camera in the B and R bands, covering a total region of 67.22x32.94 arcmin^2, or 4.235x2.075 Mpc^2 for a cluster redshift of 0.0539. In a region of 500 kpc radius around the cluster centre, the GLF in the R band shows a double structure, with a broad and flat bright part and a flat faint end that can be fit by a power law with an index alpha=-0.85+-0.12 in the 20.25<R<21.75 interval. If we divide this 500 kpc radius region in North+South or East+West halves, we find no clear difference between the GLFs in these smaller regions. No obvious large scale structure is apparent within 5 Mpc from the cluster, based on galaxy redshifts and magnitudes collected from the NED database in a much larger region than that covered by our data, suggesting that there is no major infall of material in any preferential direction. However, the Serna-Gerbal method reveals the presence of a gravitationally bound structure of 27 galaxies, which includes the cD, and of a more strongly gravitationally bound structure of 14 galaxies. These optical results agree with the overall relaxed structure of Abell 780 previously derived from X-ray analyses.

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arXiv2006

Galaxy clusters in the CFHTLS. First matched filter candidate catalogue of the Deep fields

We apply a matched-filter cluster detection algorithm to the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) i-band data for the Deep-1, Deep-2, Deep-3 and Deep-4 fields covering a total of 4square degrees. To test the implemented procedure we carry out simulations for assessing the frequency of noise peaks as well as estimate the recovery efficiency. We estimate that up to z~0.7 the catalogue is essentially complete for clusters of richness class R>~1. The recovered redshifts are in general overestimated by dz=0.1 with a scatter of sigma_dz~0.1, except at redshifts z>~1 where the estimated redshifts are systematically underestimated. The constructed cluster candidate catalogue contains 162 detections over an effective area of 3.112 square degrees corresponding to a density of ~52.1 per square degree. The median estimated redshift of the candidates is z=0.6. The estimated noise frequency is 16.9+-5.4 detections per square degree. From visual inspection we identify systems that show a clear concentration of galaxies with similar colour. These systems have a density of ~20 per square degree.

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arXiv2006

Diffuse light and building history of the galaxy cluster Abell 2667

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

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arXiv2005

Star formation in the merging galaxy cluster Abell 3921

Through a combined optical and radio analysis, we have investigated the possible connection between the dynamical state of the merging cluster A3921 and its star formation properties, reaching the conclusion that the on-going merger is triggering a SF episode in the collision region.

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arXiv2004

Large scale diffuse light in the Coma cluster: a multi-scale approach

We have obtained wide field images of the Coma cluster in the B, V, R and I bands with the CFH12K camera at CFHT. In order to search for large scale diffuse emission, we have applied to these images an iterative multi scale wavelet analysis and reconstruction technique which allowed to model all the sources (stars and galaxies) and subtract them from the original images. We found various concentrations of diffuse emission present in the central zone around the central galaxies NGC4874 and NGC4889. We characterize the positions, sizes and colors of these concentrations. Some sources do not seem to have strong star formation, while another one probably exhibits spiral-like color. One possible origin for the star forming diffuse emission sources is that in the region of the two main galaxies NGC4874 and NGC4889 spiral galaxies have recently been disrupted and star formation is still active in the dispersed material. We also use the characteristics of the sources of diffuse emission to trace the cluster dynamics. A scenario in which the group around NGC 4874 is moving north is consistent with our data.

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arXiv2004

Dynamical state and star formation properties of the merging galaxy cluster Abell 3921

We present the results of a new spectroscopic and photometric survey of the central region of the galaxy cluster A3921 (z=0.094). We detect the presence of two dominant clumps of galaxies: a main cluster centred on the BCG (A3921-A), and a NW sub-cluster (A3921-B) hosting the second brightest cluster galaxy. The distorted morphology of the two sub-clusters suggests that they are interacting, while the velocity distribution of 104 confirmed cluster members does not reveal strong signatures of merging. By applying a two-body dynamical formalism to the two sub-clusters of A3921, and by comparing our optical results to the X-ray analysis of A3921 based on XMM observations (Belsole et al. 2004), we conclude that A3921-B is probably tangentially traversing the main cluster along a SW/NE direction. Our estimate of the star formation properties of the cluster members reveals substantial fractions of both emission-line (~13%) and post-star-forming objects (k+a's,~16%). A lack of bright k+a's with respect to higher redshift clusters is observed, while the fraction of k+a's increases towards fainter magnitudes. The spatial and velocity distributions of k+a's galaxies, their red colours and their moderate Balmer absorption lines suggest that their presence is difficult to relate to the on-going merging event. Star forming galaxies, which are mostly concentrated in A3921-B and between the two sub-clusters, share neither the same kinematics, nor the same projected distribution of the passive cluster members. Their spectral properties may be at least partly realted to the ongoing merger.

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arXiv2004

The Large Scale Distribution of Galaxies in the Shapley Supercluster

We present new results of our wide-field redshift survey of galaxies in a 182 square degree region of the Shapley Supercluster (SSC) based on observations with the FLAIR-II spectrograph on the UK Schmidt Telescope. We present new measurements to give a total sample of redshifts for 710 bright (R<16.6) galaxies, of which 464 are members of the SSC (8000<v<18000 kms). Our data reveal that the main plane of the SSC extends further than previously realised, filling the whole extent of our survey region of 10 degrees by 20 degrees on the sky (35 Mpc by 70 Mpc). There is also a significant structure associated with the slightly nearer Abell 3571 cluster complex with a caustic structure evident out to a radius of 6 Mpc. These galaxies seem to link two previously identified sheets of galaxies and establish a connection with a third one at v=15000 kms. They also tend to fill the gap of galaxies between the foreground Hydra-Centaurus region and the more distant SSC. We calculate galaxy overdensities of 5.0+/-0.1 over the 182 square degree region surveyed and 3.3+/-0.1 in a 159 square degree region excluding rich clusters.

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arXiv2001

A multiscale regularized restoration algorithm for XMM-Newton data

We introduce a new multiscale restoration algorithm for images with few photons counts and its use for denoising XMM data. We use a thresholding of the wavelet space so as to remove the noise contribution at each scale while preserving the multiscale information of the signal. Contrary to other algorithms the signal restoration process is the same whatever the signal to noise ratio is. Thresholds according to a Poisson noise process are indeed computed analytically at each scale thanks to the use of the unnormalized Haar wavelet transform. Promising preliminary results are obtained on X-ray data for Abell 2163 with the computation of a temperature map.

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arXiv1999

Abell 521: Dynamical analysis of a young cluster

We present the results of a dynamical analysis of the rich X-Ray luminous galaxy cluster Abell 521, and discuss the nature of the arc-like structure first noted by Maurogordato et al. (1996). Our study is based on radial velocities for 41 cluster members, measured from spectra obtained at the European Southern Observatory and the Canada-France-Hawaii Telescope. We find that Abell 521 is an intermediate-redshift cluster (CBI= 74132 (-250,+202)km/s) with a rather high apparent value of the velocity dispersion (SBI= 1386 (-139,+206) km/s). This high value, which cannot be explained by trivial projection effects, and the significant clumping in the two-dimensional projected positions of the galaxies in the cluster indicate it is still undergoing strong dynamical evolution. The two brightest knots of the giant arc candidate are shown to be at the velocity of the cluster. This makes the gravitational lensing interpretation for the bright curved structure very improbable, although gravitational lensing might still be present in this cluster, as suggested by the colors of two fainter arclet-like structures.

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arXiv1999

New Structure In The Shapley Supercluster

We present new radial velocities for 306 bright (R<16) galaxies in a 77 square deg region of the Shapley supercluster measured with the FLAIR-II spectrograph on the UK Schmidt Telescope. The galaxies we measured were uniformly distributed over the survey area in contrast to previous samples which were concentrated in several rich Abell clusters. Most of the galaxies (230) were members of the Shapley supercluster: they trace out two previously unknown sheets of galaxies linking the Abell clusters of the supercluster. In a 44 square deg area of the supercluster excluding the Abell clusters, these sheets alone represent an overdensity of a factor of 2.0+/-0.2 compared to a uniform galaxy distribution. The supercluster is not flattened in the Declination direction as was suggested in previous papers. Within our survey area the new galaxies contribute an additional 50% to the known contents of the Shapley supercluster with a corresponding increase in its contribution to the motion of the local group.

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arXiv1998

New Structure In The Shapley Supercluster

We present new radial velocities for 189 galaxies in a 91 sq. deg region of the Shapley supercluster measured with the FLAIR-II spectrograph on the UK Schmidt Telescope. The data reveal two sheets of galaxies linking the major concentrations of the supercluster. The supercluster is not flattened in Declination as was suggested previously and it may be at least 30 percent larger than previously thought with a correspondingly larger contribution to the motion of the Local Group.

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arXiv1997

A photometric catalogue of galaxies in the cluster Abell 85

We present two catalogues of galaxies in the direction of the rich cluster \a85. The first one includes 4,232 galaxies located in a region $\pm 1^\circ$ from the cluster centre. It has been obtained from a list of more than 25,000 galaxy candidates detected by scanning a Schmidt photographic plate taken in the \bj 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 (805 galaxies) gives a list of galaxies with CCD magnitudes in the V and R bands for a much smaller region in the centre of the cluster. These two catalogues will be combined with a redshift catalogue of 509 galaxies (Durret et al. 1997; astro-ph/9709298) to investigate the cluster properties at optical wavelengths (Durret et al. in preparation), as a complement to our previous X-ray studies (Pislar et al. 1997, Lima-Neto et al. 1997).

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arXiv1997

A catalogue of velocities in the cluster of galaxies Abell 85

We present a catalogue of velocities for 551 galaxies (and give the coordinates of 39 stars misclassified as galaxies in our photometric plate catalogue) in a region covering about 100'$\times$100' (0.94$\times$0.94 Mpc for an average redshift of 0.0555, assuming H$_\circ$=50 km s$^{-1}$ Mpc$^{-1}$) in the direction of the rich cluster Abell 85. This catalogue includes previously published redshifts by Beers et al. (1991) and Malumuth et al. (1992), together with our 367 new measurements. A total of 305 galaxies have velocities in the interval 13350-20000 km s$^{-1}$, and will be considered as members of the cluster. Abell 85 therefore becomes one of the clusters with the highest number of measured redshifts; its optical properties are being investigated in a companion paper.

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arXiv1997

The rich cluster of galaxies ABCG 85. II. X-ray analysis using the ROSAT HRI

We present a new X-ray analysis mainly based on ROSAT HRI data. The HRI spatial resolution combined with an improved wavelet analysis method and with complementary radio and optical data provides new results compared to a previous paper based on ROSAT PSPC data (Pislar et al. 1997). We use also redshift data in order to identify galaxies dynamically belonging to the main body of the cluster and/or to superimposed substructures. Various kinds of emission are superimposed on a mean thermal X-ray emission due to the intra-cluster gas: a) an X-ray flux excess in the centre; b) a south blob, partially generated by individual galaxies. The mean velocity and velocity dispersion of the galaxies located in this region are the same as those of the cluster as a whole: it therefore does not seem to be a bound subgroup; c) West emission due to a foreground group with self-emission from a Seyfert galaxy located at the north-west; d) emission in the south-west due to inverse Compton emission associated to a very steep radio source (the remnant of an active galactic nucleus). We have examined the possibility for the central peak to be an "unusual" galaxy, as assumed for the central galaxy of J2310-43 (Tananbaum et al. 1997). We conclude on the existence of a cooling flow region, in which the presence of at least three small features certainly related to cooler blobs is revealed by the wavelet analysis. We have performed a pixel-to-pixel modelling of the double X-ray emission. The large scale emission component is comparable to those derived from by the PSPC data and the small scale one is interpreted as a cooling-flow. A multiphase gas model analysis leads to a mass deposit of 50-150 M_\odot/yr.

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arXiv1997

The rich cluster of galaxies ABCG 85.I. X-ray analysis

We present an X-ray analysis of the rich cluster ABCG 85 based on ROSAT PSPC data. By applying an improved wavelet analysis, we show that our view of this cluster is notably changed from what was previously believed (a main region and a south blob). The main emission comes from the central part of the main body of the cluster on which is superimposed that of a foreground group of galaxies. The foreground group and the main cluster are separated (if redshifts are cosmological) by 46 1/h_50 Mpc. The southern blob is clearly not a group: it is resolved into X-ray emitting galaxies (in particular the second more luminous galaxy of the main cluster). Several X-ray features are identified with bright galaxies. We performed a spectral analysis and derived the temperature (T), metallicity (Z) and hydrogen column density NH. The global quantities are: T=4keV (in agreement with the velocity dispersion of 760km/s) and $Z=0.2Z_\odot$. We cannot derive accurate gradients for these quantities with our data, but there is strong evidence that the temperature is lower ($\sim 2.8 keV$) and the metallicity much higher (Z $\sim 0.8 Z_\odot$) in the very centre (within about 50 1/h_50 kpc). We present a pixel by pixel method to model the physical properties of the X-ray gas and derive its density distribution. We apply classical methods to estimate the dynamical, gas and stellar masses, as well as the cooling time and cooling flow characteristics. At the limiting radius of the image (1.4 1/h_50 Mpc), we find $M_{\rm Dyn}\sim (2.1-2.9)10^{14} 1/h_50 M$_{\odot}$, $M_{gas}/M_{Dyn}\sim 0.18 h_{50}^{-1.5}$. The stellar mass is $6.7\ 10^{12}M_{\odot}$, giving a mass to light ratio of $M/L_{V}\sim 300$. The cooling time is estimated for different models, leading to a cooling radius of 30-80 kpc depending on the

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arXiv1996

A photometric catalogue of the Coma cluster core

We have obtained a mosaic of CCD images of the Coma cluster in the V-band covering a region of approximately 0.4 degrees$^2$ around both central cluster galaxies NGC 4889 and NGC 4874. An additional frame of $\sim$ 90 arcmin$^2$ was taken of the south-west region around NGC 4839. We derived a catalogue of 7023 galaxies and 4096 stars containing positions, central surface brightnesses and isophotal V$_{26.5}$ magnitudes. We estimate that data is complete up to V $_{26.5}\sim$ 22.5 and the surface brightness limiting detection value is $μ$ $\sim$ 24 mag/arcsec$^2$. In this paper we present the catalogue (available in electronic form alone), along with a detailed description of the steps concerning the data reduction and quality of the computed parameters.

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