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We use test-particle integrations to show that epicyclic motions excited by apericentre passage of a dwarf galaxy could account for bulk vertical velocitystreaming motions recently observed in the Galactic stellar disc near the Sun.We use fixed potential test-particle integrations to isolate the role of phasewrapping of epicyclic perturbations from bending and breathing waves or modes,which require self-gravity to oscillate. Perturbations from a fairly massiveSagittarius dwarf galaxy, $M_d \sim 2.5 \times 10^{10} M_\odot$, are requiredto account for the size of the observed streaming motions from its orbitalpericentre approximately a Gyr ago. A previous passage of the dwarf through theGalactic disc approximately 2.2 Gyr ago (with a then more massive dwarf galaxy)is less effective. If phase wrapping of epicyclic perturbations is responsiblefor stellar streaming motions in the Galactic disc, then there should bevariations in velocity gradients on scales of a few kpc in the vicinity of theSun.

Phase Wrapping of Epicyclic Perturbations in the Wobbly Galaxy