IC3328: a "dwarf elliptical galaxy" with spiral structure

TL;DR

This paper reports the discovery of a faint, tightly wound spiral structure in the dwarf elliptical galaxy IC3328, challenging traditional views on dwarf galaxy morphology and dynamics.

Contribution

It provides the first detailed photometric analysis revealing a spiral pattern in a dwarf elliptical galaxy, suggesting possible rotational support or tidal origins.

Findings

Discovery of the faintest and smallest spiral in a galaxy.

Spiral structure similar to M51 but without gas or dust.

Evidence suggesting a nearly face-on disk galaxy with rotation.

Abstract

We present the 2-D photometric decomposition of the Virgo galaxy IC3328. The analysis of the global light distribution of this morphologically classified nucleated dwarf elliptical galaxy (dE1,N) reveals a tightly wound, bi-symmetric spiral structure with a diameter of 4.5 kpc, precisely centered on the nucleus of the dwarf. The amplitude of the spiral is only three percent of the dwarf's surface brightness making it the faintest and smallest spiral ever found in a galaxy. In terms of pitch angle and arm winding the spiral is similar to the intermediate-type galaxy M51, but it lacks the dust and prominent HII regions which signal the presence of gas. The visual evidence of a spiral pattern in an early-type dwarf galaxy reopens the question on whether these dwarfs are genuine rotationally supported or anisotropic stellar systems. In the case of IC3328, we argue for a nearly face-on disk (dS0) galaxy with an estimated maximum rotation velocity of v_c,max = 55kms-1. The faintness of the spiral and the small motions within it, suggests that we could be seeing swing-amplified noise. The other possibility is a tidal origin, caused by the near passage of a small companion.