On the flattening of dark haloes

Approximately self-consistent disc–halo systems with Stäckel potentials are used to investigate the flattening of a massive galactic halo. If the kinematics of the objects that bear the mass of the halo are similar to those of extreme Population II stars, then: (i) the massive halo should have an axis ratio b/a≲0.5; (ii) most of this flattening will be intrinsic to the halo, rather than a reflection of the gravitational attraction of the disc; and (iii) the density of the dark halo near the Sun will be two or more times that anticipated if the halo were spherical. Such an increase in the local halo density would reduce by up to half the discrepancy between the dynamically measured local disc surface density and inventories of the solar neighbourhood compiled from electromagnetic measurements.