The Sagittarius stellar stream embedded in a fermionic dark matter halo

¹ Instituto de Astrofísica de La Plata (CONICET-UNLP), Paseo del Bosque S/N, La Plata 1900, Buenos Aires, Argentina
² Facultad de Ciencias Astronómicas y Geofísicas de La Plata (UNLP), Paseo del Bosque S/N, La Plata 1900, Buenos Aires, Argentina
³ ICRANet, Piazza della Repubblica 10, 65122 Pescara, Italy

^* Corresponding author: scollazo@fcaglp.unlp.edu.ar

Received: 24 May 2024
Accepted: 14 May 2025

Abstract

Context. Stellar streams are essential tracers of the gravitational potential of the Milky Way, with key implications for the problem of dark matter model distributions, either within or beyond phenomenological ΛCDM halos.

Aims. For the first time in the literature, a dark matter (DM) halo model based on first physical principles such as (quantum) statistical mechanics and thermodynamics is used to try to reproduce the 6D observations of the Sagittarius (Sgr) stream. Thus, we aim to extract quantitative and qualitative conclusions on how well our assumptions stand with respect to the observations. We model both DM halos, the one of the Sgr dwarf and the one of its host, with a spherical self-gravitating system of neutral fermions that accounts for the effects of particle escape and fermion degeneracy (due to the Pauli exclusion principle), the latter causing a high-density core at the center of the halo. Full baryonic components for each galaxy are also considered.

Methods. We used a spray algorithm with ∼ 10⁵ particles to generate the Sgr tidal debris, which evolves in the combined gravitational potential of the host-progenitor system, to then make a direct comparison with the full phase-space data of the stream. We repeated this kind of simulation for different parameter setups of the fermionic model including the particle mass, with special attention to testing different DM halo morphologies allowed by the physics, including polytropic density tails as well as power-law-like trends.

Results. We find that the fermionic halo models considered can only reproduce the trailing arm of the Sgr stream. Within the observationally allowed span of enclosed masses where the stream moves, neither the power-law-like nor the polytropic behavior of the fermionic halo models can answer for the observed trend of the leading tail – a conclusion that is shared by former analyses using other types of spherically symmetric halos. Thus, we conclude that further model improvements, such as abandoning spherical symmetry and including the Large Magellanic Cloud perturber, are needed for the proper modeling of the overall Milky Way potential within this kind of first-principle halo model.