Complexity on dwarf galaxies scale: A bimodal distribution function in Sculptor

TL;DR

This study reveals that the dwarf galaxy Sculptor has a bimodal distribution function in energy and angular momentum space, indicating two distinct dynamical components and a complex formation history.

Contribution

It provides the first dynamical confirmation of two separate components in Sculptor using non-parametric distribution functions without prior stellar population data.

Findings

Bimodal distribution function in energy and angular momentum space

Confirmation of two distinct dynamical components in Sculptor

Implication of complex assembly history

Abstract

In previous work we have presented Schwarzschild models of the Sculptor dSph, demonstrating that this system could be embedded in dark matter halos that are either cusped or cored. Here we show that the non-parametric distribution function recovered through Schwarschild's method is bimodal in energy and angular momentum space for all best fitting mass models explored. We demonstrate that this bimodality is directly related to the two components known to be present in Sculptor through stellar populations analysis, although our method is purely dynamical in nature and does not use this prior information. It therefore constitutes independent confirmation of the existence of two physically distinct dynamical components in Sculptor and suggests a rather complex assembly history for this dwarf galaxy.