  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.

Astrophysics