Galaxy structure searches by photometric redshifts in the CFHTLS

Abstract

Context. Counting clusters is one of the methods to constrain cosmological parameters, but has been limited up to now both by the redshift range and by the relatively small sizes of the homogeneously surveyed areas. Aims. 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 Canada France Hawaii Telescope Legacy Survey (CFHTLS). Methods. We considered the deep 2, 3 and 4 CFHTLS Deep fields (each 1 × 1 deg 2 ), as well as the wide 1, 3 and 4 CFHTLS Wide fields. We used the Le Phare photometric redshifts for the galaxies detected in these fields 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 at various detection levels. 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, including filaments, by applying a minimal spanning tree algorithm both to our data and to the Millennium simulations. Results. We 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 ) in the CFHTLS Deep and Wide fields, 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 ≥ 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. Conclusions. We have shown that a search for galaxy clusters based on density maps built from galaxy catalogs in photometric redshift bins is successful and gives results comparable to or better than those obtained with other methods. By applying this technique to the CFHTLS survey we have increased the number of known optical high redshift cluster candidates by a large factor, an important step towards using cluster counts to measure cosmological parameters.

The XMM-LSS survey: optical assessment and properties of different X-ray selected cluster classes

“…However, these clusters are identified on the basis of the color−magnitude relation (for two of them) or are detected as significant galaxy overdensities in Adami et al (2010) using photometric redshifts during the analysis. All these objects have been classified as C0 clusters.…”

“…-We first selected only clusters at z ≤ 0.5 in order to be able to sample the galaxy population deeply enough to potentially detect the filaments, given the i = 23 magnitude limit for the photometric redshift catalog as demonstrated in Adami et al (2010); -for a given cluster, we selected galaxies with photometric redshifts in a 0.04 × (1 + z) slice around the cluster redshift; -we then computed the number of galaxies in the slice in 72 angular sectors 10 degrees wide each, with position angles between 0 and 360 degrees. Each sector was overlapping the previous one by 5 degrees.…”

Observational probes of cosmic acceleration

“…3669 is the number of 4σ cluster candidates. Milkeraitis et al, 2010;Adami et al, 2010), the SDSS has led to the publication of several moderately deep (z 0.5) and wide catalogs, which can contain upwards of 50,000 clusters (e.g. Koester et al, 2007;Wen et al, 2009;Hao et al, 2010;Szabo et al, 2011).…”

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

“…However, we cannot use the full sample for several reasons. First, we demonstrated in Adami et al (2010) that the CFHTLS Wide samples are not well suited to detecting large-scale structures (LSS) as cosmological filaments at z ≥ 0.5, so we limit the sample here to z ≤ 0.5 candidate clusters. Second, we need a precise cluster centre localization in order not to bias the surrounding LSS detection.…”