More evidence for hidden spiral and bar features in bright early-type dwarf galaxies^*

¹ Astronomisches Institut, Universität Basel, Venusstrasse 7, 4102 Binningen, Switzerland
² Research School of Astronomy and Astrophysics, The Australian National University, Mt Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia

Corresponding author: F. D. Barazza, barazza@astro.unibas.ch

Received: 25 February 2002
Accepted: 31 May 2002

Abstract

Following the discovery of spiral structure in IC 3328 (Jerjen et al. [CITE]), we present further evidence that a sizable fraction of bright early-type dwarfs in the Virgo cluster are genuine disk galaxies, or are hosting a disk component. Among a sample of 23 nucleated dwarf ellipticals and dS0s observed with the Very Large Telescope in B and R, we found another four systems exhibiting non-axisymmetric structures, such as a bar and/or spiral arms, indicative of a disk (IC 0783, IC 3349, NGC 4431, IC 3468). Particularly remarkable are the two-armed spiral pattern in IC 0783 and the bar and trailing arms in NGC 4431. For both galaxies the disk nature has recently been confirmed by a rotation velocity measurement (Simien & Prugniel [CITE]). Our photometric search is based on a Fourier decomposition method and a specific version of unsharp masking. Some “early-type” dwarfs in the Virgo cluster seem to be former late-type galaxies which were transformed to early-type morphology, e.g. by “harassment”, during their infall to the cluster, while maintaining part of their disk structure.