Isophotometry of a sample of 175 brightest cluster ellipticals (BCEs) is presented and discussed. Over half the sample is measured out to a distance along the major axis of 50 kpc (H0 = 60 km s-1 kpc-1, q0 = 1/2). Profiles of major- and minor-axis surface brightness, ellipticity, position angle, and isophote centroid are derived. The average ellipticity of BCEs is a strongly increasing function of metric radius. Fewer than a quarter of this sample show significant amounts of ellipticity decrease with increasing radius anywhere in their surface brightness profiles, seventeen have roughly constant ellipticities, and six at most have steadily decreasing ellipticity profiles. At radii less than 16 kpc, BCEs are rounder than the average elliptical, but at radii greater than about 30 kpc, they become so predominantly flattened that they cannot represent a randomly oriented population of oblate spheroids. At radii larger than 3 kpc, they are strongly aligned with the distribution of galaxies and x-ray gas in clusters. However, their shape (local) parameters are not otherwise correlated with their global properties or the global properties of the clusters they inhabit. At least 20% of the galaxies in the sample show isophote twists greater than 40°, and a comparable number show significant nonconcentricity. Thirteen BCEs, primarily multiple-nucleus systems, show both. These results are evidence that at least the outer regions of BCEs are dynamically strongly coupled to their clusters, which are very prolate or stringy, and suggests that at least some galaxy growth continues to the present day.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science