The XXL Survey IX. Optical overdensity and radio continuum analysis of a supercluster at z=0.43
Journal article, 2016

We present observations with the Karl G. Jansky Very Large Array (VLA) at 3 GHz (10 cm) toward a sub-field of the XXL-North 25 deg(2) field targeting the first supercluster discovered in the XXL Survey. The structure has been found at a spectroscopic redshift of 0.43 and extending over 0.degrees 35x0.degrees 1 on the sky. The aim of this paper is twofold. First, we present the 3 GHz VLA radio continuum observations, the final radio mosaic and radio source catalogue, and, second, we perform a detailed analysis of the supercluster in the optical and radio regimes using photometric redshifts from the CFHTLS survey and our new VLA-XXL data. Our final 3 GHz radio mosaic has a resolution of 3 ''.2 x 1 ''.9, and encompasses an area of 41'x41' with rms noise level lower than similar to 20 mu Jy beam(-1). The noise in the central 15'x15' region is approximate to 11 mu Jy beam(-1). From the mosaic we extract a catalogue of 155 radio sources with signal-to-noise ratio (S/N) >= 6, eight of which are large, multicomponent sources, and 123 (79%) of which can be associated with optical sources in the CFHTLS W1 catalogue. Applying Voronoi tessellation analysis (VTA) in the area around the X-ray identified supercluster using photometric redshifts from the CFHTLS survey we identify a total of seventeen overdensities at z(phot) = 0.35-0.50, 7 of which are associated with clusters detected in the XMM-Newton XXL data. We find a mean photometric redshift of 0.43 for our overdensities, consistent with the spectroscopic redshifts of the brightest cluster galaxies of seven X-ray detected clusters. The full VTA-identified structure extends over similar to 0.degrees 6x0.degrees 2on the sky, which corresponds to a physical size of similar to 12x4 Mpc(2) at z = 0.43. No large radio galaxies are present within the overdensities, and we associate eight (S/N > 7) radio sources with potential group/cluster member galaxies. The spatial distribution of the red and blue VTA-identified potential group member galaxies, selected by their observed g -r colours, suggests that the clusters are not virialised yet, but are dynamically young, as expected for hierarchical structure growth in a Lambda CDM universe. Further spectroscopic data are required to analyse the dynamical state of the groups.


radio continuum: galaxies

galaxies: groups: general

galaxies: clusters: general


N. Baran

University of Zagreb

V. Smolcic

University of Zagreb

D. Milakovic

University of Zagreb

M. Novak

University of Zagreb

J. Delhaize

University of Zagreb

F. Gastaldello

INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan

M. E. Ramos-Ceja

Argelander-Institut für Astronomie

F. Pacaud

Argelander-Institut für Astronomie

S. Bourke

California Institute of Technology (Caltech)

C. L. Carilli

National Radio Astronomy Observatory Socorro

S. Ettori

Osservatorio Astronomico Di Bologna

G. Hallinan

California Institute of Technology (Caltech)

Cathy Horellou

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

E. Koulouridis

The French Alternative Energies and Atomic Energy Commission (CEA)

L. Chiappetti

INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan

O. Miettinen

University of Zagreb

O. Melnyk

University of Zagreb

Taras Shevchenko National University of Kyiv

K. Mooley

California Institute of Technology (Caltech)

M. Pierre

The French Alternative Energies and Atomic Energy Commission (CEA)

E. Pompei

European Southern Observatory Santiago

E. Schinnerer

Max Planck Society

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 592 A8

Subject Categories

Astronomy, Astrophysics and Cosmology


Basic sciences



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