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arXiv · 2506.11845

Chemo-dynamics of the stellar component of the Sculptor dwarf galaxy II: dynamical properties and dark matter halo density

José María Arroyo Polonio·Raffaele Pascale·Giuseppina Battaglia·Guillaume F. Thomas·Carlo Nipoti·Eugene Vasiliev·Eline Tolstoy
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Abstract

Dwarf galaxies satellite of the Milky Way are excellent laboratories for testing dark matter (DM) models and baryonic feedback implementation in simulations. The Sculptor 'classical' dwarf spheroidal galaxy, a system with two distinct stellar populations and high-quality data, offers a remarkable opportunity to study DM distributions in these galaxies. In this work, we infer the DM halo density distribution of Sculptor, applying a method based on spherically symmetric distribution functions depending on actions to fit the stellar structural and kinematic properties of Sculptor. The galaxy is represented via four components: two distinct stellar populations based on distribution functions, tracers within a fixed and dominant DM potential, plus the contribution of a third stellar component that accounts for possible sources of contamination. The model-data comparison accounts for the kinematics and metallicities of individual stars, allowing us to assign probabilities of membership to each star. The modeling is applied on the largest available set of spectroscopic data, which have not been previously analyzed with this objective. We find the DM distribution of Sculptor to have a logarithmic inner slope of 0.39+0.23-0.26 and a scale radius of 0.79+0.38-0.17 kpc at 1 sigma confidence level. Our results show that Sculptor DM density profile deviates from predictions of DM-only simulations at a 3 sigma level over a large range of radii. Our analysis suggests that the velocity distribution of Sculptor's two main stellar components is isotropic in the center and becomes radially anisotropic in the outskirts. Additionally, we provide predictions for the projected radial and tangential velocity dispersion profiles. We also present updated DM annihilation and decay J- and D-factors, finding J = 18.15+0.11-0.12 and D = 18.07+0.10-0.10 for an angular aperture of 0.5 degrees.

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José María Arroyo Polonio, Raffaele Pascale, Giuseppina Battaglia, Guillaume F. Thomas, Carlo Nipoti, Eugene Vasiliev, Eline Tolstoy. 2025-06-13. Chemo-dynamics of the stellar component of the Sculptor dwarf galaxy II: dynamical properties and dark matter halo density. https://arxiv.org/abs/2506.11845

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