We analyse the structure of the local stellar halo of the Milky Way using \sim 60 000 stars with full phase space coordinates extracted from the SDSS– Gaia catalogue .
We display stars in action space as a function of metallicity in a realistic axisymmetric potential for the Milky Way Galaxy .
The metal-rich population is more distended towards high radial action J _ { R } as compared to azimuthal or vertical action , J _ { \phi } or J _ { z } .
It has a mild prograde rotation ( \langle v _ { \phi } \rangle \approx 25 km s ^ { -1 } ) , is radially anisotropic and highly flattened with axis ratio q \approx 0.6 - 0.7 .
The metal-poor population is more evenly distributed in all three actions .
It has larger prograde rotation ( \langle v _ { \phi } \rangle \approx 50 km s ^ { -1 } ) , a mild radial anisotropy and a roundish morphology ( q \approx 0.9 ) .
We identify two further components of the halo in action space .
There is a high energy , retrograde component that is only present in the metal-rich stars .
This is suggestive of an origin in a retrograde encounter , possibly the one that created the stripped dwarf galaxy nucleus , \omega Centauri .
Also visible as a distinct entity in action space is a resonant component , which is flattened and prograde .
It extends over a range of metallicities down to [ Fe/H ] \approx - 3 .
It has a net outward radial velocity \langle v _ { R } \rangle \approx 12 km s ^ { -1 } within the Solar circle at |z| < 3.5 kpc .
The existence of resonant stars at such extremely low metallicities has not been seen before .