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The ATLAS 3D project - XXIV. The intrinsic shape distribution of early-type galaxies

Weijmans, A.-M., de Zeeuw, P. T., Emsellem, E., Krajnovi, D., Lablanche, P.-Y., Alatalo, K., Blitz, L., Bois, M., Bournaud, F., Bureau, M., Cappellari, M., Crocker, A. F., Davies, R. L., Davis, Timothy A., Duc, P.-A., Khochfar, S., Kuntschner, H., McDermid, R. M., Morganti, R., Naab, T., Oosterloo, T., Sarzi, M., Scott, N., Serra, P., Verdoes Kleijn, G. and Young, L. M. 2014. The ATLAS 3D project - XXIV. The intrinsic shape distribution of early-type galaxies. Monthly Notices of the Royal Astronomical Society 444 (4) , pp. 3340-3356. 10.1093/mnras/stu1603

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Abstract

We use the ATLAS3D sample to perform a study of the intrinsic shapes of early-type galaxies, taking advantage of the available combined photometric and kinematic data. Based on our ellipticity measurements from the Sloan Digital Sky Survey Data Release 7, and additional imaging from the Isaac Newton Telescope, we first invert the shape distribution of fast and slow rotators under the assumption of axisymmetry. The so-obtained intrinsic shape distribution for the fast rotators can be described with a Gaussian with a mean flattening of q = 0.25 and standard deviation σq = 0.14, and an additional tail towards rounder shapes. The slow rotators are much rounder, and are well described with a Gaussian with mean q = 0.63 and σq = 0.09. We then checked that our results were consistent when applying a different and independent method to obtain intrinsic shape distributions, by fitting the observed ellipticity distributions directly using Gaussian parametrizations for the intrinsic axis ratios. Although both fast and slow rotators are identified as early-type galaxies in morphological studies, and in many previous shape studies are therefore grouped together, their shape distributions are significantly different, hinting at different formation scenarios. The intrinsic shape distribution of the fast rotators shows similarities with the spiral galaxy population. Including the observed kinematic misalignment in our intrinsic shape study shows that the fast rotators are predominantly axisymmetric, with only very little room for triaxiality. For the slow rotators though there are very strong indications that they are (mildly) triaxial

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Publisher: Oxford University Press
ISSN: 0035-8711
Date of Acceptance: 5 August 2014
Last Modified: 21 Feb 2019 12:18
URI: http://orca.cf.ac.uk/id/eprint/87979

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