Dark halo structure in the Carina dwarf spheroidal galaxy: joint analysis of multiple stellar components

TL;DR

This study models the dark matter halo of the Carina dwarf galaxy using multiple stellar populations, revealing a larger, less cuspy halo and providing insights into its tidal evolution and dark matter properties.

Contribution

Developed non-spherical dynamical models incorporating multiple stellar populations to constrain Carina's dark halo structure and its implications for dark matter detection.

Findings

Carina has a larger, denser, less cuspy dark halo than previous estimates.

Both stellar populations exhibit radial anisotropy in the inner regions.

Outer regions show tangential bias in older populations, indicating tidal effects.

Abstract

Photometric and spectroscopic observations of the Carina dSph revealed that this galaxy contains two dominant stellar populations of different age and kinematics. The co-existence of multiple populations provides new constraints on the dark halo structure of the galaxy, because different populations should be in equilibrium in the same dark matter potential well. We develop non-spherical dynamical models including such multiple stellar components and attempt to constrain the properties of the non-spherical dark halo of Carina. We find that Carina probably has a larger and denser dark halo than found in previous works and a less cuspy inner dark matter density profile, even though the uncertainties of dark halo parameters are still large due to small volume of data sample. Using our fitting results, we evaluate astrophysical factors for dark matter annihilation and decay and find that Carina should be one of the most promising detectable targets among classical dSph galaxies. We also calculate stellar velocity anisotropy profiles for both stellar populations and find that they are both radially anisotropic in the inner regions, while in the outer regions the older population becomes more tangentially biased than the intermediate one. This is consistent with the anisotropy predicted from tidal effects on the dynamical structure of a satellite galaxy and thereby can be considered as kinematic evidence for the tidal evolution of Carina.