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The σ-bump in elliptical galaxies – a signature of major mergers?

Published online by Cambridge University Press:  21 March 2017

Anna T. P. Schauer
Affiliation:
Zentrum für Astronomie der Universität Heidelberg, ITA, Germany
Felix Schulze
Affiliation:
Universitäts-Sternwarte München, Scheinerstr. 1, D-81679 München, Germany
Rhea-Silvia Remus
Affiliation:
Universitäts-Sternwarte München, Scheinerstr. 1, D-81679 München, Germany
Andreas Burkert
Affiliation:
Universitäts-Sternwarte München, Scheinerstr. 1, D-81679 München, Germany MPI for Extraterrestrial Physics, P.O. Box 1312, D-85748 Garching, Germany email: schauer@uni-heidelberg.de
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Abstract

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The stellar radial velocity dispersion profiles of elliptical galaxies can be well described by a power-law σ(r)∝r−β. We analyze a set of elliptical galaxies formed by major mergers of isolated disk galaxies with mass ratios of 1:1 and 3:1 for several orbital configurations (Johansson et al. 2009). The galaxies in our sample show a deviation from the power-law at 1 − 3Reff, which we term the σ-bump (Schauer et al. 2014). This feature is most prominent in remnants of 1:1 mergers and weakens for remnants of mergers with smaller mass ratios, indicating that the σ-bump is a signature of an equal mass merger. The σ-bump does not vanish with time but stays constant once it has formed, in contrast to shells. It can be seen under all projections, making it an observable feature in the outskirts of elliptical galaxies. We indeed identify three possible σ-bump candidates in the sample of 12 SLUGGS-survey ellipticals studied by Pota et al. (2013), who use globular clusters as tracers for the outer stellar halos (see Schauer et al. 2014, for more details). For further comparisons, we here provide for the first time a two dimensional map of the velocity dispersion of one simulated σ-bump galaxy, to identify the σ-bump in observations of kinematic maps out to several Reff. The σ-bump appears as a global ring-like feature if seen face-on and as an extended box-like feature in its edge-on projection.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2017 

References

Johansson, P. H., Burkert, A., & Naab, T. 2009, ApJL, 707, L184 CrossRefGoogle Scholar
Pota, V., Forbes, D. A., Romanowsky, A. J., et al. 2013, MNRAS, 428, 389 CrossRefGoogle Scholar
Schauer, A. T. P., Remus, R.-S., Burkert, A., & Johansson, P. H. 2014, ApJL, 783, L32 CrossRefGoogle Scholar