GHOSTS IN THE ATTIC: MAPPING THE STELLAR CONTENT OF THE S0 GALAXY NGC 5102

The spatial distribution of stars in the nearby S0 galaxy NGC 5102 is investigated using images obtained with WIRCam and MegaCam on the Canada-France-Hawaii Telescope. With the exception of gaps between detector elements, the entire galaxy is surveyed in r' and i', while the J and Ks data extend out to R GC ∼ 6 kpc, which corresponds to almost 7 disk scale lengths. A modest population of main-sequence stars with MV < -3.5 and ages ∼70 Myr are detected throughout the disk, with the majority located in the southern half of the galaxy. The stellar disk in the northern half of the galaxy is warped, following structure that is also seen in H I. Objects with photometric properties that are consistent with those of bright asymptotic giant branch (AGB) stars are seen throughout the disk, and the ratio of C stars to bright M giants is consistent with an overall increase in the star formation rate within the past 1 Gyr. Star-forming activity during the interval 0.1-2 Gyr was more centrally concentrated than during the past ∼100 Myr. The structure of the disk changes near R GC ∼ 5 kpc (5.5 disk scale lengths), in the sense that the radial surface density profile defined by red supergiants (RSGs) and bright AGB stars levels off at larger radii. RSGs and bright AGB stars are traced out to a radius of 14 kpc (15.6 scale lengths) along the southern portion of the major axis, while a tentative detection is also made of bright AGB stars at a projected distance of ∼16 kpc along the southeast minor axis. A large clump of AGB stars that subtends ∼1 arcmin is identified to the west of the galaxy center. It is argued that this is the remnant of a companion galaxy that triggered past episodes of elevated star-forming activity.