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Evidence for a Large Stellar Bar in the LSB Galaxy UGC 7321

M. Pohlen·M. Balcells·R. Luetticke·R. -J. Dettmar
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Abstract

Late-type spiral galaxies are thought to be the dynamically simplest type of disk galaxies and our understanding of their properties plays a key role in the 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 those 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.

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M. Pohlen, M. Balcells, R. Luetticke, R. -J. Dettmar. 2003-07-16. Evidence for a Large Stellar Bar in the LSB Galaxy UGC 7321. https://doi.org/10.1051/0004-6361%3A20031091

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