But they're in the halo. Can they actually be gravitationally bound at that distance at those velocities? Is even the (computed by other means) amount of dark matter enough for them to be captured?
Also, “in the halo” doesn’t necessarily mean “far from the center of the galaxy”; it means “not orbiting in the disk”.[1] Some of these stars are closer to the galactic center than the Sun.
[1] And further away from the center of the galaxy than the bulge — but the bulge is much smaller than the orbit of the Sun.