Specific angular momentum of disc merger remnants and the λR-parameter |
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Authors: | Roland Jesseit Michele Cappellari Thorsten Naab Eric Emsellem Andreas Burkert |
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Affiliation: | Universitätssternwarte München, Scheinerstr 1, 81679 München, Germany;Sub-department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH;Universitéde Lyon, Lyon, F-69003, France;UniversitéLyon 1, Observatoire de Lyon, 9 avenue Charles André, Saint-Genis Laval, F-69230, France;CNRS, UMR 5574, Centre de Recherche Astrophysique de Lyon;Ecole Normale Supérieure de Lyon, Lyon, F-69007, France |
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Abstract: | We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the λR -parameter, which is a luminosity-weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early-type galaxies in so-called fast λR > 0.1 and slow rotators λR < 0.1 . Tests on merger remnants reveal that λR is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of λR values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in transforming fast rotators into slow rotators in a single binary merger, the latter being created mostly in an equal-mass merger. Slow rotators have a λR which does not vary with projection. The confusion rate with face-on fast rotators is very small. Mergers with a gas component form slow rotators with smaller ellipticities than collisionless merger remnants have, and are in much better agreement with the SAURON slow rotators. Remergers of merger remnants are slow rotators, but tend to have too high ellipticities. Fast rotators maintain the angular momentum content from the progenitor disc galaxy if merger mass ratio is high. Some SAURON galaxies have values of λ R as high as our progenitor disc galaxies. |
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Keywords: | methods: N-body simulations galaxies: elliptical and lenticular, cD galaxies: evolution galaxies: formation galaxies: fundamental parameters galaxies: kinematics and dynamics |
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