An analytic galaxy model with ρ∼r−1 at small radii and ρ∼r−3.5 at large radii is presented. The asymptotic density fall-off is
slower than the Hernquist model, but faster than the Navarro-Frenk-White (NFW)
profile for dark matter haloes, and so in accord with recent evidence from
cosmological simulations. The model provides the zeroth-order term in a
biorthornomal basis function expansion, meaning that axisymmetric, triaxial and
lopsided distortions can easily be added (much like the Hernquist model itself
which is the zeroth-order term of the Hernquist-Ostriker expansion). The
properties of the spherical model, including analytic distribution functions
which are either isotropic, radially anisotropic or tangentially anisotropic,
are discussed in some detail. The analogue of the mass-concentration relation
for cosmological haloes is provided.EJL and JLS acknowledge financial support from the Science and Technology Facilities Council