EDP Sciences
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Volume 409, Number 2, October II 2003
Page(s) 485 - 490
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20031091

A&A 409, 485-490 (2003)
DOI: 10.1051/0004-6361:20031091

Evidence for a large stellar bar in the Low Surface Brightness galaxy UGC 7321

M. Pohlen1, 2, M. Balcells1, R. Lütticke3, 2 and R.-J. Dettmar2

1  Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
    e-mail: pohlen,balcells@ll.iac.es
2  Astronomical Institute, Ruhr-Universität Bochum, 44780 Bochum, Germany
    e-mail: dettmar@astro.rub.de
3  Department of Computer Science, FernUniversität Hagen, 58084 Hagen, Germany
    e-mail: Rainer.Luetticke@FernUni-Hagen.de

(Received 6 June 2003 / Accepted 7 July 2003 )

Late-type spiral galaxies are thought to be the dynamically simplest type of disk galaxy and our understanding of their properties plays a key role in galaxy formation and evolution scenarios. The low surface brightness (LSB) galaxy UGC 7321, a nearby, isolated, "superthin" edge-on galaxy, is an ideal object to study these purely disk-dominated bulge-less galaxies. Although late type spirals are believed to exhibit the simplest possible structure, even prior observations showed deviations from a pure single component exponential disk in the case of UGC 7321. We present for the first time photometric evidence for peanut-shaped outer isophotes from a deep optical ( R-band) image of UGC 7321. Observations and dynamical modeling suggest that boxy/peanut-shaped (b/p) bulges in general form through the buckling instability in bars of the parent galaxy disks. Together with recent HI observations supporting the presence of a stellar bar in UGC 7321, this could be the earliest known case of the buckling process during the evolutionary life of a LSB galaxy, whereby material in the disk-bar has started to be pumped up above the disk, but a genuine bulge has not yet formed.

Key words: galaxies: spiral -- galaxies: structure -- galaxies: fundamental parameters -- galaxies: evolution -- galaxies: peculiar -- galaxies: individual: UGC 7321

Offprint request: M. Pohlen, pohlen@ll.iac.es

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© ESO 2003