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Astron. Astrophys. 358, 845-849 (2000)

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IC3328: A "dwarf elliptical galaxy" with spiral structure *

H. Jerjen 1, A. Kalnajs 1 and B. Binggeli 2

1 Australian National University, Research School of Astronomy and Astrophysics, Private Bag, Weston Creek PO, ACT 2611, Canberra, Australia
2 Universität Basel, Astronomisches Institut, Venusstrasse 7, 4102 Binningen, Switzerland

Received 20 March 2000 / Accepted 13 April 2000

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 [FORMULA] km s-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.

Key words: galaxies: dwarf – galaxies: elliptical and lenticular, cD – galaxies: individual: IC3328 – galaxies: interactions – galaxies: kinematics and dynamics – galaxies: structure

* Based on observations collected at the European Southern Observatory (ESO 63.O-0055)

Send offprint requests to: H. Jerjen (jerjen@mso.anu.edu.au)

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© European Southern Observatory (ESO) 2000

Online publication: June 20, 2000
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