def NFW_model(r3d_kpc, norm, rs):
    """
    Compute a NFW model

    Parameters
    ----------
    - r3d_kpc (kpc): array of radius
    - norm : the normalization 
    - rs (kpc): characteristic radius parameter

    Outputs
    --------
    - NFW model profile as a function of the input radius vector

    """
    
    return norm / (r3d_kpc / rs) / (1 + (r3d_kpc / rs))**2