Browsing by Author "Way, MJ"

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    Deconstruction Abell 3266: A major merger in a quiet cluster
    (2000) Flores, RA; Quintana, H; Way, MJ
    We present results of simple N-body simulations that strengthen the suggestion that Abell 3266 is composed of two subunits of comparable mass that have merged recently. Both the real cluster and the N-body dark-matter cluster show mixed signals of substructure under statistical tests. However, in a decidedly nonstatistical approach allowed by the wide-area coverage and the large number of redshifts Quintana, Ramirez, & Way measured in A3266, they sliced the real cluster in redshift space to uncover a peculiar spatial distribution of galaxies that they suggested was the result of a recent merger. In our simulations, a similar distribution is the result of an ongoing merger between two comparable-mass units that started about 2 x 10(9) yr ago in the N-body simulations. We also find that the distribution of emission-line galaxies in A3266 traces the same structure. We discuss further tests of our merger hypothesis and speculate on the possibility that a similar process might be occurring in other, apparently relaxed clusters at the present epoch.
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    Dynamics of the cluster of galaxies A3266 (Sersic 40/6) .1. Spectroscopic data
    (1996) Quintana, H; Ramirez, A; Way, MJ
    We present 387 velocities covering an area 1.8 degrees x1.8 degrees, including 229 new galaxy velocities obtained from 309 spectra, of which 317 appear to be cluster members according to our analysis. Based on this extended velocity sample we reanalyzed the velocity structure of the cluster. We found a strongly decreasing velocity dispersion profile that, as well as the mean velocity, shows significant radial scatter. Inside the 2.5h(50)(-1) Mpc radius, the velocity dispersion has a value of 1306+/-73 km s(-1), while further out than 3h(50)(-1) Mpc it falls below 800 km s(-1). The global dispersion is 1085+/-51 km s(-1). We found a remarkable velocity substructure, which we interpret as a tidal outgoing arm reaching from the center to the northernmost extensions surveyed. The arm could be produced by a recent merger with another cluster, that moved from the front and SW direction and scattered from the main cluster core into the arm. This model allows us to derive an epoch for the collision between the more massive core and the front edge of the incoming cluster of 4X10(9)h(50)(-1) yr ago and of similar to 2X10(9)h(50)(-1) yr for the merging of both cores. Formation of the dumb-bell is a later merger process of the two BCMs, consistent with theoretical estimates. The collision picture is also consistent with the distorted x-ray image. The very northernmost parts of the arm could, alternatively, be interpreted as ongoing infall of a few outlying loose groups. The suggestion of a faint galaxy system within 400h(50)(-1) kpc, satellite to the central dumb-bell, is maintained in spite of the large central velocity dispersion value; however, confirmation requires data for further compact faint members. From several mass estimators we derived a cluster dynamical mass value of 5X10(15)h(50)(-1) M(.), but this value should be seen in the merger context described. (C) 1996 American Astronomical Society.
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    Spectroscopy of the NGC 4782/3 dumbbell dominated group of galaxies: Dark haloes and merger of subgroups
    (1996) Quintana, H; Ramirez, A; Way, MJ
    A nearly complete sample of new velocities for 96 galaxies covering an area 1 degrees X1.25 degrees centered on NGC 4782/3 are presented, Including data from the literature a total of 125 velocities are compiled. We deduce that 40 galaxies are likely members of the group centered on NGC 4782/3, more than doubling the original confirmed 13 members. Based on this extended velocity sample we analyze the velocity structure of this unusual group. A bi-modal velocity structure centered on each of the dumbbell components provides evidence for an ongoing collision of two subgroups associated to these components. In velocity space the richer subgroup is centered on the more massive NGC 4782. From the subgroup dynamics we derive approximate dynamical masses of 5X10(13) M. and 1X10(13) M. for the NGC 4782 and NGC 4783 subgroups, respectively, This leads to a group M/L approximate to 300 (M/L)., implying that similar to 90% of the group mass is in dark form, within subsystems associated to each subgroup, The colliding elliptical galaxies have massive haloes which should be important in shaping the outcome of the collision and merger process, In particular, haloes could change the interpretation of the tidal distortions and play a role in the shaping of the radio double bent jet structure of 3C 278. (C) 1996 American Astronomical Society.
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    Velocity dispersions and cluster properties in the Southern Abell Redshift Survey clusters. II.
    (2002) Muriel, H; Quintana, H; Infante, L; Lambas, DG; Way, MJ
    We report an analysis of the dynamical structure of clusters of galaxies from a survey of photometric and spectroscopic observations in the fields of southern Abell clusters. We analyze the galaxy velocity field in extended regions up to 7 h(-1) Mpc from cluster centers, and we estimate mean velocity dispersions and their radial dependence. Only one from a total of 41 Abell clusters does not correspond to a dynamically bound system. However, four of these bound objects are double clusters. We estimate that 20% (seven clusters) of the 35 remaining are subject to serious projection effects. Normalizing the clustercentric distances by means of the overdensity radius r(200), and the velocity dispersion profiles (VDPs) by the corresponding mean cluster velocity dispersion, we computed the average VDP. Our results indicate a at behavior of the mean VDP at large distances from the cluster center. Nevertheless, we found that for the inner part of the clusters (r/r(200)less than or equal to1) the VDP is up to 10% smaller than at larger radii.