IC3328: A "dwarf elliptical galaxy" with spiral structure

We present the 2-D photometric decomposition of the Virgo salary IC3328. Th e analysis of the global light distribution of this morphologically classif ied nucleated dwarf elliptical galaxy (dE 1,N) reveals a tightly wound, bi- symmetric spiral structure with a diameter of 4.5 kpc, precisely centered o n the nucleus of the dwarf. The amplitude of the spiral is only three perce nt of the dwarf's surface brightness making it the faintest and smallest sp iral ever found in a galaxy. In terms of pitch angle and arm winding the sp iral is similar to the intermediate-type galaxy M51, but it lacks the dust and prominent I-III regions which signal the presence of gas. The visual ev idence of a spiral pattern in an early-type dwarf galaxy reopens the questi on on whether these dwarfs are genuine rotationally supported or anisotropi c stellar systems. In the case of IC3328, we argue for a nearly face-on dis k (dS0) galaxy with an estimated maximum rotation velocity of nu(c,max) app roximate to 55 km s(-1). The faintness of the spiral and the small motions within it, suggests that we could be seeing swing-amplified noise. The othe r possibility is a tidal origin, caused by the near passage of a small comp anion.