POSSIBLE STELLAR STREAMS IN THE EDGE-ON SPIRAL NGC 891 DISCOVERED FROM KINEMATICS OF PLANETARY NEBULAE

We have found 125 planetary nebulae (PNs) in NGC 891, using an [O III] λ5007 on-band/off-band filter technique with the Faint Object Camera and Spectrograph (FOCAS) at the Cassegrain focus of the Subaru telescope, Mauna Kea. Radial velocities were measured for all detected sources, using a method of slitless spectroscopy which we briefly describe. The radial velocities allow us to study the motions of different stellar populations in NGC 891. The PN kinematics show rotation at large distances from the galactic plane. Of particular interest is the strong asymmetry of PN distribution at large height, which we interpret as two possible stellar streams that could be orbiting the galaxy at large angles to the main structure. These streams, if real, are probably remnants of a previous minor merging episode. This idea finds support in recent reports of clump-like, incompletely mixed structures from deep HST/ACS images of this galaxy.