Nuclear stellar disks in spiral galaxies

We report evidence for nuclear stellar disks in three early-type spirals, namely, NGC 1425, NGC 3898, and NGC 4698, revealed by Wide Field Planetary Camera 2 F606W images out of a sample of 38 spiral galaxies, selected from the Hubble Space Telescope data archive. Adopting the photometric method introduced by Scorza & Bender, we derived their central surface brightness and scale length by assuming them to be infinitesimally thin exponential disks. No nuclear disk was found in barred galaxies or galaxies of Hubble type later than Sb. The external origin of the disk in NGC 4698 is strongly suggested by its orthogonal geometrical decoupling with respect to the host galaxy.