NFWProfil

NFWProfil is a software tool and modeling framework designed to describe the distribution of dark matter in astrophysical halos using the Navarro-Frenk-White (NFW) density profile. It provides both the mathematical description of the profile and practical utilities for fitting to observational data, enabling researchers to infer halo properties from measurements such as rotation curves, gravitational lensing, or satellite kinematics.

The NFW density profile expresses the three-dimensional density as rho(r) = rho_s / [(r/r_s)(1 + r/r_s)^2], where r_s is the scale radius and rho_s is the corresponding scale density. An equivalent parameterization uses the virial radius R200 and the concentration parameter c = R200/r_s. The cumulative mass follows M(r) = 4π rho_s r_s^3 [ln(1 + r/r_s) − (r/r_s)/(1 + r/r_s)]. In terms of M200 and c, rho_s and r_s can be derived, linking the profile to common halo properties.

NFWProfil implements both the three-dimensional profile and the projected quantities relevant for observations, including the surface density Sigma(R) and the tangential shear required for lensing analyses. The package supports numerical evaluation of these quantities and, in many configurations, analytic expressions are provided for efficiency.

Key features include parameter estimation from data via optimization or Bayesian inference, support for common data products (rotation curves, lensing signals, kinematic tracers), and outputs such as best-fit values for M200 and c, uncertainties, and parameter covariances. The toolkit is designed to be compatible with standard astronomical data formats and with visualization and sampling libraries to aid interpretation.

Limitations of NFWProfil reflect the broader NFW model: the assumption of spherical symmetry, potential baryonic effects in the inner regions, and degeneracies between scale parameters. Users typically combine NFWProfil with additional constraints to mitigate these issues. See also the Navarro-Frenk-White profile, dark matter halos, and gravitational lensing.