Substructure analysis of selected low-richness 2dFGRS clusters of galaxies

William S. Burgett 13 Michael M. Vick 12 David S. Davis 10 18 Matthew Colless 16 17 Roberto De Propris 16 Ivan Baldry 15 Carlton Baugh 20 Joss Bland-Hawthorn 17 Terry Bridges 19 Russell Cannon 17 Shaun Cole 20 Chris Collins 14 Warrick Couch 7 Nicholas Cross 15 Gavin Dalton 5 8 Simon Driver 16 George Efstathiou 6 Richard Ellis 3 Carlos S. Frenk 20 Karl Glazebrook 15 Edward Hawkins 4 Carole Jackson 1 Ofer Lahav 6 Ian Lewis 8 Stuart Lumsden 2 Steve Maddox 4 Darren Madgwick 0 Peder Norberg 11 John A. Peacock 9 Will Percival 9 Bruce Peterson 16 Will Sutherland 9 Keith Taylor 3 0 Lawrence Berkeley National Laboratory , 1 Cyclotron Rd., Berkeley, CA 94720 , USA 1 CSIRO Australia Telescope National Facility , PO Box 76, Epping, NSW 1710 , Australia 2 Department of Physics, University of Leeds , Woodhouse Lane, Leeds LS2 9JT 3 Department of Astronomy, California Institute of Technology , Pasadena, CA 91125 , USA 4 School of Physics & Astronomy, University of Nottingham , Nottingham NG7 2RD 5 Rutherford Appleton Laboratory , Chilton, Didcot OX11 0QX 6 Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA 7 Department of Astrophysics, University of New South Wales , Sydney, NSW 2052 , Australia 8 Department of Physics, University of Oxford , Keble Road, Oxford OX1 3RH 9 Institute for Astronomy, University of Edinburgh , Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ 10 Joint Center for Astrophysics, Department of Physics , UMBC, Baltimore, MD 21250 USA 11 ETHZ Institut fur Astronomie , HPF G3.1, ETH Honggerberg, CH-8093, Zurich , Switzerland 12 Department of Physics, University of Texas at Dallas , Richardson, TX 75083-0688 , USA 13 Institute for Astronomy, University of Hawaii , 2680 Woodlawn Dr., Honolulu, HI 96822 , USA 14 Astrophysics Research Institute, Liverpool John Moores University , Twelve Quays House, Birkenhead L14 1LD 15 Department of Physics & Astronomy, Johns Hopkins University , Baltimore MD 21218-2686 , USA 16 Research School of Astronomy & Astrophysics, The Australian National University , Weston Creek, ACT 2611 , Australia 17 Anglo-Australian Observatory , PO Box 296, Epping, NSW 2121 , Australia 18 Laboratory for High Energy Astrophysics, NASA GSFC , Code 662, Greenbelt MD 20771 , USA 19 Physics Department, Queen's University , Kingston, ON, K7L 3N6 , Canada 20 Department of Physics, University of Durham , South Road, Durham DH1 3LE A B S T R A C T Complementary one-, two- and three-dimensional tests for detecting the presence of substructure in clusters of galaxies are applied to recently obtained data from the 2dF Galaxy Redshift Survey. The sample of 25 clusters used in this study includes 16 clusters not previously investigated for substructure. Substructure is detected at or greater than the 99 per cent confidence level in at least one test for 21 of the 25 clusters studied here. From the results, it appears that low-richness clusters commonly contain subclusters participating in mergers. About half of the clusters have two or more components within 0.5 h1 Mpc of the cluster centroid, and at least three clusters (Abell 1139, Abell 1663 and Abell S333) exhibit velocity-position characteristics consistent with the presence of possible cluster rotation, shear, or infall dynamics. The geometry of certain features is consistent with influence by the host supercluster environments. In general, our results support the hypothesis that low-richness clusters relax to structureless equilibrium states on very long dynamical time-scales (if at all). - RA (J2000) [h : m : s.] 10:7:1.32 10:13:38.42 10:58:10.98 11:22:54.36 12:50:3.89 13:2:52.55 13:31:11.00 0:11:21.60 0:42:8.82 2:30:49.41 3:11:25.00 22:27:54.49 23:31:50.89 23:30:22.62 23:47:34.92 1:13:47.09 2:25:44.44 2:49:33.72 3:15:9.95 22:36:27.96 2:29:55.78 23:41:35.49 23:56:27.66 23:55:8.44 0:25:31.36 Dec. (J2000) [ : : . ] 5:37:28.7 0:55:32.6 1:36:16.4 1:6:51.2 1:32:26.7 2:31:4.0 1:43:42.0 28:51:6.6 28:32:8.8 33:6:11.7 26:55:52.2 30:34:31.3 34:3:16.6 34:56:48.3 28:7:29.3 31:44:53.0 29:36:57.5 31:11:23.2 29:14:37.4 24:20:30.8 33:10:37.2 29:14:10.9 34:35:35.0 32:44:26.0 33:2:47.6 d p(t e) d p(t 0) RACO 1 I N T R O D U C T I O N 2 G L O B A L C L U S T E R P R O P E R T I E S 2.1 Cluster centroid and ellipticity A and B are the solutions of 10 = x , 01 = y, xi2 x 2, yi2 y2, xi yi x y, i=1 the semiprincipal axes of the ellipse 20 02 2 = 0. 02 B ) being the semimajor axis, and the ellipticity is = 1 A B h1Mpc 1.00 Ac Bc (h1 Mpc) (h1 Mpc) Rc Ac Bc Abell 930 Abell 957 Abell 1139 Abell 1238 Abell 1620 Abell 1663 Abell 1750 Abell 2734 Abell 2814 Abell 3027 Abell 3094 Abell 3880 Abell 4012 Abell 4013 Abell 4038 Abell S141 Abell S258 Abell S301 Abell S333 Abell S1043 APM 268 APM 917 APM 933 EDCC 365 EDCC 442 Abell 930 Abell 957 Abell 1139 Abell 1238 Abell 1620 Abell 1663 Abell 1750 Abell 2734 Abell 2814 Abell 3027 Abell 3094 Abell 3880 Abell 4012 Abell 4013 Abell 4038 Abell S141 Abell S258 Abell S301 Abell S333 Abell S1043 APM 268 APM 917 APM 933 EDCC 365 EDCC 442 2.2 Density profiles and core fitting 0 (r ) = 1 + (r /Rc)2 , 0 (x , y) = 1 + (x / A)2 + (y/B)2 n(r ) = Rc20 ln r (n) = Rc exp n/Rc20 1. 2(Rc, 0) = i=1 ri r (i ) 2 0.47 0.01 0.16 0.01 0.26 0.01 0.41 0.02 0.47 0.02 0.46 0.03 0.39 0.03 0.31 0.01 0.36 0.01 0.29 0.01 0.39 0.01 0.25 0.01 0.28 0.01 0.17 0.01 0.19 0.01 0.26 0.02 0.28 0.04 0.24 0.01 0.35 0.01 0.31 0.01 0.30 0.01 0.14 0.01 0.36 0.01 0.37 0.01 0.33 0.01 = 2 = 2 Rc Rc = i=1 i=1 Rc = 0 = 0, exp n/Rc20 1 exp n/Rc20 1 A2R=1 = 1. Given the coordinates (xi, yi) of the ith galaxy in the cluster, there exists a concentric ellipse which includes the coordinate (xi, yi) defined by and Ri = Ai Bi , with Ri satisfying Ri = R=1 A2R=1 The circular core-fitting technique described above can now be utilized in the following manner: Ri = R=1 Rc = Ac Bc. (a) Circularly Symmetric Fit (b) Elliptically Symmetric Fit R0c == 309.5172 0.031 R0c == 701.2783 0.007 20 40 60 Galaxies within r(n) 20 40 60 Galaxies within R(n) i=1 (vi v)3 The kurtosis coefficient is defined as (vi v)4 3. Skewness 1 2 3 4 Skewness/(15/N) 1 2 3 4 Kurtosis3/(96/N) 3.2 Contour, segmentation, and nearest neighbour visualization plots CL to reject Gaussian (per cent) Taylor expansion to first order in z (see, e.g. Peebles 1993, pp. 328 330), 3.3 The test (i) Convert (RA, Dec.) sky coordinates to Cartesian coordinates (x, y), and calculate the centroid of the two-dimensional galaxy distribution, i=1 i=1 (ii) Assign a weight wi = 1/ i to each galaxy, where i is the line-of-sight velocity dispersion for galaxy i and its N nn nearest neighbours, where an arbitrary choice is made to set Nnn = N . (iii) For each galaxy i and its N nn nearest neighbours, calculate the weighted centroid, (v) Finally, the statistic quantifies the cluster substructure as an average of the i values, 3.4 The test = 1000 i . 3.5 The test i=1 log[ PKS(D > Dobs)], (...truncated)