Eric Slezak

Gaia Universe model snapshot - A statistical analysis of the expected contents of the Gaia catalogue

Context. This study has been developed in the framework of the computational simulations that are executed for the preparation of the ESA Gaia astrometric mission. Aims. We focus on describing the objects and characteristics that Gaia will potentially observe without taking into consideration instrumental effects (detection efficiency, observing errors). Methods. The theoretical Universe model prepared for the Gaia simulation has been statistically analysed at a given time. Ingredients of the model are described, with the greatest emplasis on the stellar content, the double and multiple stars, and variability. Results. In this simulation the errors have not yet been included. Hence we estimated the number of objects and their theoretical photometric, astrometric and spectroscopic characteristics if they are perfectly detected. We show that Gaia will be able to potentially observe 1.1 billion of stars (single or part of multiple star systems) of which about 2% are variable stars and 3% have one or two exoplanets. At the extragalactic level, observations will be potentially composed of several millions of galaxies, half a million to 1 million quasars and about 50 000 supernovae that will occur during the five years of the mission.

A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory

Elliptical Galaxy Evolution Our closest elliptical galaxy, M32, represents a rare class of elliptical galaxies that are too compact for their luminosities. Only a handful of elliptical galaxies with luminosities and sizes comparable to M32 have been found, making it difficult to understand how they evolved. Chilingarian et al. (p. 1379, published online 1 October) present a sample of 21 compact elliptical galaxies gathered through automated data mining of the Hubble Space Telescope Legacy Archive and other databases by means of virtual observatory tools. The results suggest that tidal stripping of more massive progenitor galaxies produces compact elliptical galaxies. A sample of elliptical systems provides evidence that disruption of galaxies plays an important role in their evolution. 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.

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. To search for large scale diffuse emission, we have applied to these images an iterative multiscale wavelet analysis and reconstruction technique which made it possible 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 NGC 4874 and NGC 4889. We characterize the positions, sizes and colors of these concentrations. Some sources do not seem to have strong star formation, while one probably exhibits spiral-like colors. One possible origin for the star forming diffuse emission sources is that in the region of the two main galaxies NGC 4874 and NGC 4889 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.

Structure and dynamics of the Shapley Supercluster - Velocity catalogue, general morphology and mass

We present results of our wide-field redshift survey of galaxies in a 285 square degree region of the Shapley Supercluster (SSC), based on a set of 10 529 velocity measurements (including 1201 new ones) on 8632 galaxies obtained from various telescopes and from the literature. Our data reveal that the main plane of the SSC (v ≈ 14 500 km s −1 ) extends further than previous estimates, filling the whole extent of our survey region of 12 degrees by 30 degrees on the sky (30 × 75 h −1 Mpc). There is also a connecting structure associated with the slightly nearer Abell 3571 cluster complex (v ≈ 12 000 km s −1 ). These galaxies seem to link two previously identified sheets of galaxies and establish a connection with a third one at v = 15 000 km s −1 near RA = 13 h . They also tend to fill the gap of galaxies between the foreground Hydra-Centaurus region and the more distant SSC. In the velocity range of the Shapley Supercluster (9000 km s −1 < cz < 18 000 km s −1 ), we found redshift-space overdensities with bj < 17. 5o f� 5.4 over the 225 square degree central region and � 3.8 in a 192 square degree region excluding rich clusters. Over the large region of our survey, we find that the intercluster galaxies make up 48 per cent of the observed galaxies in the SSC region and, accounting for the different completeness, may contribute nearly twice as much mass as the cluster galaxies. In this paper, we discuss the completeness of the velocity catalogue, the morphology of the supercluster, the global overdensity, and some properties of the individual galaxy clusters in the Supercluster.

Density estimation with non–parametric methods

One key issue in several astrophysical prob- lems is the evaluation of the density probability function underlying an observational discrete data set. We here review two non-parametric density estimators which re- cently appeared in the astrophysical literature, namely the adaptive kernel density estimator and the Maximum Penalized Likelihood technique, and describe another method based on the wavelet transform. The eciency of these estimators is tested by using ex- tensive numerical simulations in the one-dimensional case. The results are in good agreement with theoretical func- tions and the three methods appear to yield consistent es- timates. However, the Maximum Penalized Likelihood suf- fers from a lack of resolution and high computational cost due to its dependency on a minimization algorithm. The small dierences between kernel and wavelet estimates are mainly explained by the ability of the wavelet method to take into account local gaps in the data distribution. This new approach is very promising, since smaller struc- tures superimposed onto a larger one are detected only by this technique, especially when small samples are investi- gated. Thus, wavelet solutions appear to be better suited for subclustering studies. Nevertheless, kernel estimates seem more robust and are reliable solutions although some small-scale details can be missed. In order to check these estimators with respect to pre- vious studies, two galaxy redshift samples, related to the galaxy cluster A3526 and to the Corona Borealis region, have been analyzed. In both these cases claims for bi- modality are conrmed at a high condence level.

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.

Restoration of Astrophysical Spectra With Sparsity Constraints: Models and Algorithms

We address the problem of joint signal restoration and parameter estimation in the context of the forthcoming MUSE instrument, which will provide spectroscopic measurements of light emitted by very distant galaxies. Restoration of spectra is formulated as a linear inverse problem, accounting for the instrument response and the noise spectral variability. Estimation is considered in the setting of sparse approximation, where restoration is performed jointly with the detection of relevant patterns in the spectra. To this aim, a dictionary of elementary spectral features is designed according to astrophysical spectroscopy. Sparse estimation is considered through the minimization of a quadratic data misfit criterion with an ℓ1-norm penalization, where nonzero components are associated to the detected features. An efficient optimization strategy is proposed, based on the Iterative Coordinate Descent (ICD) principle, with accelerations that dramatically reduce the computational cost. The algorithm does not rely on fast transforms and can be applied to a wide variety of criteria if the sparsity constraint is separable. Results on simulated MUSE-like data reveal satisfactory performance in terms of denoising and detection of physically relevant spectral features. On such data, the proposed algorithm is shown to outperform both state-of-the-art gradient-based and homotopy continuation methods. Simulations with a compressed sensing-like random matrix also reveal better performance compared with usual algorithms, showing that ICD can be a powerful strategy for sparse optimization.

Intracluster light in clusters of galaxies at redshifts 0.4 < z < 0.8

Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305-4060,USAAccepted . Received ; Draft printed: September 21, 2011ABSTRACTContext.The study of intracluster light (ICL) can help us to understand the mechanisms taking place in galaxy clusters, andto place constraints on the cluster formation history and physical properties. However, owing to the intrinsic faintness of ICLemission, most searches and detailed studies of ICL have been limited to redshifts z< 0.4.Aims.To help us extend our knowledge of ICL properties to higher redshifts and study the evolution of ICL with redshift, wesearch for ICL in a subsample of ten clusters detected by the ESO Distant Cluster Survey (EDisCS), at redshifts 0.4 <z< 0.8,that are also part of our DAFT/FADA Survey.Methods.We analyze the ICL by applying the OV WAV package, a wavelet-based technique, to deep HST ACS images in theF814W filter and to V-band VLT/FORS2 images of three clusters. Detection levels are assessed as a function of the diffuse lightsource surface brightness using simulations.Results. In the F814W filter images, we detect diffuse light sources in all the clusters, with typical sizes of a few tens of kpc(assuming that they are at the cluster redshifts). The ICL detected by stacking the ten F814W images shows an 8σ detection inthe source center extending over a ∼50×50 kpc

Temperature map computation for X-ray clusters of galaxies

Recent numerical simulations have shown that the variations of the gas temperature in clusters of galaxies are in- dicative of the dynamical state of these clusters. Maps of the temperature variation show complex structures with different shapes at different spatial scales, such as hot compression regions, filaments, cooling flows, or large-scale temperature pro- files. A new multiscale spectro-imagery algorithm for restoring the spatial temperature variations within clusters of galaxies is presented here. It has been especially developed to work with the EPIC MOS1, MOS2 and PN spectro-imagers on board the XMM-Newton satellite. The temperature values are fitted to an emission model that includes the source, the cosmic X-ray background and cosmic-ray induced particle background. The spatial temperature variations are coded at different scales in the wavelet space using the Haar wavelet and denoised by thresholding the wavelet coefficients. Our local temperature estimator behaves asymptotically like an optimal mininum variance bound estimator. But it is highly sensitive to the instrumental and astrophysical backgrounds, so that a good knowledge of each component of the emission model is required. Our algorithm has been applied to a simulated 60 ks observation of a merging cluster at z = 0.1. The cluster at different stages of merging has been provided by 3-D hydrodynamical simulations of structure formation (AMR). The multiscale approach has enabled us to restore the faint structures within the core of the merging subgroups where the gas emissivity is high, but also the temperature decrease at large scale in their external regions.

Galaxy cluster searches based on photometric redshifts in the four CFHTLS Wide fields

Context. Cosmological parameters can be constrained by counting clusters of galaxies as a function of mass and redshift and by considering regions of the sky sampled as deeply and as homogeneously as possible. Aims. Several methods for detecting clusters in large imaging surveys have been developed, among which the one used here, which is based on detecting structures. This method was first applied to the Canada France Hawaii Telescope Legacy Survey (CFHTLS) Deep 1 field by Mazure et al. (2007, A&A, 467, 49), then to all the Deep and Wide CFHTLS fields available in the T0004 data release by Adami et al. (2010, A&A, 509, A81). The validity of the cluster detection rate was estimated by applying the same procedure to galaxies from the Millennium simulation. Here we use the same method to analyse the full CFHTLS Wide survey, based on the T0006 data release. Methods. Our method is based on the photometric redshifts computed with Le Phare for all the galaxies detected in the Wide fields, limited to magnitudes z � ≤ 22.5. We constructed galaxy density maps in photometric redshift bins of 0.1 based on an adaptive kernel technique, detected structures with SExtractor at various detection levels, and built cluster catalogues by applying a minimal spanning tree algorithm. Results. In a total area of 154 deg 2 , we have detected 4061 candidate clusters at 3σ or above (6802 at 2σ and above), in the redshift range 0.1 ≤ z ≤ 1.15, with estimated mean masses between 1.3 × 10 14 and 12.6 × 10 14 M� . This catalogue of candidate clusters will be available at the CDS. We compare our detections with those made in various CFHTLS analyses with other methods. By stacking a subsample of clusters, we show that this subsample has typical cluster characteristics (colour−magnitude relation, galaxy luminosity function). We also confirm that the cluster-cluster correlation function is comparable to the one obtained for other cluster surveys and analyse large-scale filamentary galaxy distributions. Conclusions. We have increased the number of known optical high-redshift cluster candidates by a large factor, an important step towards obtaining reliable cluster counts to measure cosmological parameters. The clusters that we detect behave as expected if they are located at the intersection of filaments by which they are fed.