a r X i v :0704.0579v 1 [a s t r o -p h ] 4 A p r 2007
Astronomy &Astrophysics manuscript no.babbage c
ESO 2008February 1,2008
Substructures in WINGS clusters ⋆
M.Ramella 1,A.Biviano 1,A.Pisani 2,J.Varela 3,D.Bettoni 3,W.J.Couch 4,M.D’Onofrio 5,A.Dressler 6,G.Fasano 3,
P.Kjærgaard 7,M.Moles 8,E.Pignatelli 3,and B.M.Poggianti 3
1INAF /Osservatorio Astronomico di Trieste,via G.B.Tiepolo 11,I-34131,Trieste,Italy
2Istituto di Istruzione Statale Classico Dante Alighieri,Scientifico Duca degli Abruzzi,Magistrale S.Slataper,viale XX settembre 11,I-34170Gorizia,Italy
3
INAF /Osservatorio Astronomico di Padova,vicolo Osservatorio 5,I-35122,Padova,Italy 4School of Physics,University of New South Wales,Sydney 2052,Australia 5Dipartimento di Astronomia,Universit`a di Padova,vicolo Osservatorio 2,I-35122Padova,Italy 6Observatories of the Carnegie Institution of Washington,Pasadena,CA 91101,USA
7Copenhagen University Observatory.The Niels Bohr Institute for Astronomy Physics and Geophysics,Juliane Maries Vej 30,2100Copenhagen,Denmark 8
Instituto de Astrof´ısica de Andaluc´ıa (C.S.I.C.)Apartado 3004,18080Granada,Spain
Received /Accepted
ABSTRACT
Aims.We search for and characterize substructures in the projected distribution of galaxies observed in the wide field CCD images of the 77nearby clusters of the WIde-field Nearby Galaxy-cluster Survey (WINGS).This sample is complete in X-ray flux in the redshift range 0.04 Methods.We search for substructures in WINGS clusters with DEDICA,an adaptive-kernel procedure.We test the procedure on Monte-Carlo simulations of the observed frames and determine the reliability for the detected structures. Results.DEDICA identifies at least one reliable structure in the field of 55clusters.40of these clusters have a total of 69substructures at the same redshift of the cluster (redshift estimates of substructures are from color-magnitude diagrams).The fraction of clusters with subclusters (73%)is higher than in most studies.The presence of subclusters a ffects the relative luminosities of the brightest cluster galaxies (BCGs).Down to L ∼1011.2L ⊙,our observed di fferential distribution of subcluster luminosities is consistent with the theoretical prediction of the di fferential mass function of substructures in cosmological simulations.Key words.Galaxies:clusters:general –Galaxies:kinematics and dynamics 1.Introduction According to the current cosmological paradigm,large struc-tures in the Universe form hierarchically.Clusters of galaxies are the largest structures that have grown through mergers of smaller units and have achieved near dynamical equilibrium.In the hierarchical scenario,clusters are a rather young population,and we should be able to observe their formation process even at rather low redshifts.A signature of such process is the presence of cluster substructures.A cluster is said to contain substruc-tures (or subclusters)when its surface density is characterized by multiple,statistically significant peaks on scales larger than the typical galaxy size,with “surface density”being referred to the cluster galaxies,the intra-cluster (IC)gas or the dark matter (DM hereafter;Buote 2002). Studying cluster substructure therefore allows us to investi-gate the process by which clusters form,constrain the cosmo-logical model of structure formation,and ultimately test the hi-erarchical paradigm itself (e.g.Richstone et al.1992;Mohr et al.1995;Thomas et al.1998).In addition,it also allows us to better understand the mechanisms a ffecting galaxy evolution in clus-ters,which can be accelerated by the perturbative e ffects of a cluster-subcluster collision and of the tidal field experienced by
