Shaken, Not Stirred: The Disrupted Disk of the Starburst Galaxy NGC 253
  Near-infrared images obtained with the CFHT WIRCam are used to investigate
the recent history of the nearby Sculptor Group spiral NGC 253. The
distribution of stars in the disk is lop-sided, in the sense that the projected
density of AGB stars in the north east portion of the disk between 10 and 20
kpc from the galaxy center is ~ 0.5 dex higher than on the opposite side of the
galaxy. With the exception of the central 2 kpc, the north east portion of the
disk appears to have been the site of the highest levels of star-forming
activity in the galaxy during the past ~ 0.1 Gyr. Diffuse stellar structures
are found in the periphery of the disk, and the most prominent of these is to
the south and east of the galaxy. Bright AGB stars are detected out to 15 kpc
above the disk plane, and these are part of a diffusely distributed, flattened
extraplanar component. Comparisons between observed and model luminosity
functions suggest that the extraplanar regions contain stars that formed
throughout much of the age of the Universe. It is suggested that the disk of
NGC 253 was disrupted by a tidal encounter with a now defunct companion. The
ages of the youngest extraplanar stars suggests that the event that produced
the extraplanar population, and presumably induced the starburst, occured
within the past ~ 0.2 Gyr.
