A Malin 1 'cousin' with counter-rotation: internal dynamics and stellar
  content of the giant low surface brightness galaxy UGC 1922
  The formation scenario for giant low surface brightness (gLSB) galaxies with
discs as large as 100 kpc still remains unclear. These stellar systems are rare
and very hard to observe, therefore a detailed insight on every additional
object helps to understand their nature. Here we present a detailed
observational study of the gLSB UGC 1922 performed using deep optical imaging
and spectroscopic observations combined with archival ultraviolet data. We
derived spatially resolved properties of stellar and ionized gas kinematics and
characteristics of stellar populations and interstellar medium. We reveal the
presence of a kinematically decoupled central component, which counter rotates
with respect to the main disc of UGC 1922. The radial metallicity gradient of
the ionised gas is in agreement with that found for moderate-size LSB galaxies.
At the same time, a slowly rotating and dynamically hot central region of the
galaxy hosts a large number of old metal-rich stars, which creates an
appearance of a giant elliptical galaxy, that grew an enormous star forming
disc. We reproduce most of the observed features of UGC 1922 in
N-body/hydrodynamical simulations of an in-plane merger of giant Sa and Sd
galaxies. We also discuss alternative formation scenarios of this unusual
system.
