The Dark Matter Halo of the Milky Way, AD 2013 (1304.5127v2)

Abstract: We derive the mass model of the Milky Way (MW) using a cored dark matter (DM) halo profile and recent data. The method used consists in fitting a spherically symmetric model of the Galaxy with a Burkert DM halo profile to available data: MW terminal velocities in the region inside the solar circle, circular velocity as recently estimated from maser star forming regions at intermediate radii, and velocity dispersions of stellar halo tracers for the outermost Galactic region. The latter are reproduced by integrating the Jeans equation for every modeled mass distribution, and by allowing for different velocity anisotropies for different tracer populations. For comparison we also consider a Navarro-Frenk-White profile. We find that the cored profile is the preferred one, with a shallow central density of rho_H~4x10^7M_s/kpc^3 and a large core radius R_H~10 kpc, as observed in external spirals and in agreement with the mass model underlying the Universal Rotation Curve of spirals. We describe also the derived model uncertainties, which are crucially driven by the poorly constrained velocity dispersion anisotropies of halo tracers. The emerging cored DM distribution has implications for the DM annihilation angular profile, which is much less boosted in the Galactic center direction with respect to the case of the standard \Lambda CDM, NFW profile. Using the derived uncertainties we discuss finally the limitations and prospects to discriminate between cored and cusped DM profile with a possible observed diffuse DM annihilation signal. The present mass model aims to characterize the present-day description of the distribution of matter in our Galaxy, which is needed to frame current crucial issues of Cosmology, Astrophysics and Elementary Particles.

• The paper presents a mass model for the Milky Way's dark matter halo that favors the cored Burkert profile over the NFW profile.
• It uses extensive observational data, including terminal velocities, maser regions, and stellar tracers, to derive a core radius of ~10 kpc and a central density of 4×10⁷ M⊙/kpc³.
• The findings imply that dark matter annihilation signals from the Galactic center may be weaker than those predicted by cusped halo models.

Insights into the Dark Matter Halo of the Milky Way

The paper "The Dark Matter Halo of the Milky Way, AD 2013" by Fabrizio Nesti and Paolo Salucci presents a rigorous analysis of the dark matter (DM) halo surrounding the Milky Way (MW). By employing a comprehensive set of recent observational data, Nesti and Salucci construct a mass model that is instrumental for both direct and indirect DM detection methods.

Observational data, including the Milky Way's terminal velocities, the latest circular velocity estimates from maser star-forming regions, and the velocity dispersions of stellar halo tracers, underpin this mass modeling effort. The authors deploy a spherically symmetric model with a focus on two types of DM halo profiles: the cored Burkert profile and the cusped Navarro-Frenk-White (NFW) profile. Their findings suggest strong support for the Burkert profile, which is characterized by a shallow central density and a significant core radius. This result aligns with observations of external spiral galaxies, enhancing the argument for a universal rotation curve that governs spiral galaxies.

Numerical and Theoretical Outcomes

The analysis yields several important quantitative results. For the cored Burkert profile, the central dark matter density is approximately $\rho_H \sim 4 \times 10^7 \, M_\odot/\text{kpc}^3$ with a core radius $R_H \approx 10 \, \text{kpc}$. This configuration results in a total virial mass estimate of the galaxy around $1.11 \times 10^{12} \, M_\odot$, demonstrating a plausible fit to the observed rotation curves of the Milky Way. Notably, the paper highlights a significant tension between the NFW profile and the available data, especially when constrained by expectations from ΛCDM simulations regarding concentration parameters and mass distributions.

The limitations on velocity dispersion anisotropies of halo tracers prominently influence these models' uncertainties. The underestimated anisotropy hinders the conclusive differentiation between a cored and a cusped halo, particularly when considering potential diffuse annihilation signals from dark matter.

Implications for Dark Matter Annihilation

Nesti and Salucci's model has direct implications for DM annihilation signal searches. The preferred cored distribution results in less pronounced DM annihilation signals emanating from the Galactic center. This contrasts with predictions from the NFW profile, potentially reevaluating detection strategies centered on annihilation gamma rays and cosmic rays.

Prospects and Further Research

This comprehensive analysis indicates a necessity for further refinement in understanding tracer anisotropies and its implications for modeling galactic dark matter. Future work could benefit from improved constraints on velocity dispersion anisotropies and enhanced simulation accuracy incorporating baryonic feedback on DM halo structures.

Ultimately, this paper advances our understanding of the Milky Way's dark matter halo and delineates several pathways for direct and indirect dark matter detection strategies. By tightly coupling theoretical frameworks with observed data, it establishes a robust platform for ongoing astrophysical and cosmological investigations.