We present the discovery of a new dwarf galaxy , Perseus I/Andromeda XXXIII , found in the vicinity of Andromeda ( M31 ) in stacked imaging data from the Pan-STARRS1 3 \pi survey .
Located 27.9 ^ { \circ } away from M31 , Perseus I has a heliocentric distance of 785 \pm 65 { kpc } , compatible with it being a satellite of M31 at 374 ^ { +14 } _ { -10 } { kpc } from its host .
The properties of Perseus I are typical for a reasonably bright dwarf galaxy ( M _ { V } = -10.3 \pm 0.7 ) , with an exponential half-light radius of r _ { h } = 1.7 \pm 0.4 arcminutes or r _ { h } = 400 ^ { +105 } _ { -85 } { pc } at this distance , and a moderate ellipticity ( \epsilon = 0.43 ^ { +0.15 } _ { -0.17 } ) .
The late discovery of Perseus I is due to its fairly low surface brightness ( \mu _ { 0 } = 25.7 ^ { +1.0 } _ { -0.9 } mag/arcsec ^ { 2 } ) , and to the previous lack of deep , high quality photometric data in this region .
If confirmed to be a companion of M31 , the location of Perseus I , far east from its host , could place interesting constraints on the bulk motion of the satellite system of M31 .