Browsing by Author "Carrasco, ER"

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    The dwarf galaxy population of the Dorado Group down to Mv ≈-11
    (2001) Carrasco, ER; de Oliveira, CM; Infante, L; Bolte, M
    We present V and I CCD photometry of suspected low surface brightness dwarf galaxies detected in a survey covering similar to2.4 deg(2) around the central region of the Dorado group of galaxies. The low surface brightness galaxies were chosen based on their sizes and magnitudes at the limiting isophote of 26 V mu. The selected galaxies have magnitudes brighter than V approximate to 20 (M-V approximate to -11 for an assumed distance to the group of 17.2 Mpc), with central surface brightnesses mu (0) > 22.5 V mag arcsec(-2), scale lengths h > 2 ", and diameters greater than or equal to 14 " at the limiting isophote. Using these criteria, we identified 69 dwarf galaxy candidates. Four of them are large very low surface brightness galaxies that were detected on a smoothed image, after masking high surface brightness objects. Monte Carlo simulations performed to estimate completeness, photometric uncertainties and to evaluate our ability to detect extended low surface brightness galaxies show that the completeness fraction is, on average, >80% for dwarf galaxies with -17 < M-V < -10.5 and 22.5 < (0) <25.5 V mag arcsec(-2), for the range of sizes considered by us (D 14 "). The V-I colors of the dwarf candidates vary from -0.3 to 2.3 with a peak on V-I = 0.98, suggesting a range of different stellar populations in these galaxies. The projected surface density of the dwarf galaxies shows a concentration toward the group center similar in extent to that found around five X-ray groups and the elliptical galaxy NGC 1132 studied by Mulchaey & Zabludoff, suggesting that the dwarf galaxies in Dorado are probably physically associated with the overall potential well of the group.
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    The Shapley Supercluster. II. Spectroscopic observations in a wide area and general morphology
    (2000) Quintana, H; Carrasco, ER; Reisenegger, A
    We report 2868 new multiobject spectroscopic measurements of galaxy redshifts in an area roughly 12 degrees x 6 degrees (right ascension x declination) centered on the Shapley Supercluster (SSC). These correspond to 2627 different galaxies. Including other measurements reported in the literature, the total number of galaxies with measured redshifts in a 19 degrees x 16 degrees area centered on the supercluster now reaches 5090. Of these, 949 lie in the redshift range 9000-18,000 km s(-1), which we tentatively identify with the SSC. This unprecedented sample allows a quite detailed qualitative morphological study of the SSC. Based on the three-dimensional distribution of galaxies and clusters of galaxies, we identify several subcondensations of the supercluster, as well as walls and filaments connecting them. We also iind another supercluster in the background, at redshift similar to 23,000 km s(-1).
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    The shapley supercluster. III. Collapse dynamics and mass of the central concentration
    (2000) Reisenegger, A; Quintana, H; Carrasco, ER; Maze, J
    We present the first application of a spherical collapse model to a supercluster of galaxies. Positions and redshifts of similar to 3000 galaxies in the Shapley supercluster (SSC) are used to define velocity caustics that limit the gravitationally collapsing structure in its central part. This is found to extend at least to 8 h(-1) Mpc of the central cluster, A3558, enclosing 11 ACO clusters. Infall velocities reach similar to 2000 km s(-1). Dynamical models of the collapsing region are used to estimate its mass profile. An upper bound on the mass, based on a pure spherical infall model, gives M(<8 h(-1) Mpc) less than or similar to 1.3 x 10(16) h(-1) M. for an Einstein-de Sitter (critical) universe and M(<8 h(-1) Mpc) less than or similar to 8.5 x 10(15) h(-1) M. for an empty universe. The Diaferio & Geller model, based on estimating the escape velocity, gives a significantly lower value, M(<8 h(-1) Mpc) approximate to 2.1 x 10(15) h(-1) M., very similar to the mass Geller et al. found around the Coma cluster by the same method and comparable to or slightly lower than the dynamical mass in the vriialized regions of clusters enclosed in the same region of the SSC. In both models, the overdensity in this region is substantial, but it is far from the value required to account for the peculiar motion of the Local Group with respect to the cosmic microwave background.