Core shapes and orientations of core-Sersic galaxies

Abstract

The inner and outer shapes and orientations of core-Sersic galaxies may hold important clues to their formation and evolution. We have therefore measured the central and outer ellipticities and position angles for a sample of 24 core-Sersic galaxies using archival HST images and data. By selecting galaxies with core-Sersic break radii R_b---a measure of the size of their partially depleted core---that are > 0".2, we find that the ellipticities and position angles are quite robust against HST seeing. For the bulk of the galaxies, there is a good agreement between the ellipticities and position angles at the break radii and the average outer ellipticities and position angles determined over R_e/2 < R < R_e, where R_e is the spheroids' effective half light radius. However there are some interesting differences. We find a median "inner" ellipticity at R_b of e_med = 0.13 +- 0.01, rounder than the median ellipticity of the "outer" regions e_med = 0.20 +- 0.01, which is thought to reflect the influence of the central supermassive black hole at small radii. In addition, for the first time we find a trend, albeit weak (2 sigma significance), such that galaxies with larger (stellar deficit)-to- (supermassive black hole) mass ratios---thought to be a measure of the number of major dry merger events---tend to have rounder inner and outer isophotes, suggesting a connection between the galaxy shapes and their merger histories. We show that this finding is not simply reflecting the well known result that more luminous galaxies are rounder, but it is no doubt related.

9 pages, 9 figures, accepted for publication in ApJ

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• A remarkably large depleted core in the Abell 2029 BCG IC 1101
• The quest for the largest depleted galaxy core: supermassive black hole binaries and stalled in-falling satellites
• The (black hole mass)-(color) relations for early- and late-type galaxies: red and blue sequences
• Ultramassive black holes in the most massive galaxies: $M_{\mathrm{BH}}-\sigma$ versus $M_{\mathrm{BH}}-R_{\mathrm{b}}$
• The nuclear activity and central structure of the elliptical galaxy NGC 5322
• LeMMINGs. VI. Connecting nuclear activity to bulge properties of active and inactive galaxies: radio scaling relations and galaxy environment
• The most massive galaxies with large depleted cores: structural parameter relations and black hole masses