The ATLAS^(3D) project – XXIV. The intrinsic shape distribution of early-type galaxies

Creators: Weijmans, Anne-Marie; Alatalo, Katherine

Abstract

We use the ATLAS^(3D) 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 σ_q = 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 σ_q = 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.

Additional Information

© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2014 August 5. Received 2014 August 5; in original form 2013 February 9. First published online September 17, 2014. The authors thank Arjen van der Wel for kindly sharing his data, as well as fruitful discussions. The authors also thank the referee for constructive comments. This work was supported by the rolling grants Astrophysics at Oxford PP/E001114/1 and ST/H002456/1 and visitors grants PPA/V/S/2002/00553, PP/E001564/1 and ST/H504862/1 from the UK Research Councils. RLD acknowledges travel and computer grants from Christ Church, Oxford and support from the Royal Society in the form of a Wolfson Merit Award 502011.K502/jd. RLD is also grateful for support from the Australian Astronomical Observatory Distinguished Visitors programme, the ARC Centre of Excellence for All Sky Astrophysics and the University of Sydney during a sabbatical visit. MC acknowledges support from a Royal Society University Research Fellowship. SK acknowledges support from the Royal Society Joint Projects Grant JP0869822. RMMcD is supported by the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., on behalf of the international Gemini partnership of Argentina, Australia, Brazil, Canada, Chile, the United Kingdom and the United States of America. TN and MBois acknowledge support from the DFG Cluster of Excellence 'Origin and Structure of the Universe'. MS acknowledges support from a STFC Advanced Fellowship ST/F009186/1. PS acknowledges support of a NWO/Veni grant. TAD has received funding from the European Community's Seventh Framework Programme (/FP7/2007-2013/) under grant agreement No 229517. MBois has received, during this research, funding from the European Research Council under the Advanced Grant Program Num 267399-Momentum. LMY acknowledges support from NSF AST-1109803. The authors acknowledge financial support from ESO. This paper is based on observations obtained at the William Herschel Telescope and the Isaac Newton Telescope, operated by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Funding for the SDSS and SDSS-II was provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the US Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society and the Higher Education Funding Council for England. The SDSS was managed by the Astrophysical Research Consortium for the Participating Institutions. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration.

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Published - MNRAS-2014-Weijmans-3340-56.pdf

Submitted - 1408.1099v1.pdf

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