Galaxy evolution in groups. NGC 3447/NGC 3447A: the odd couple in LGG
  225
  Local Group Analogs (LGA) are galaxy associations dominated by few bright
Spirals, reminiscent of the LG. The NGC3447/NGC3447A system, member of the LGG
225 group, a nearby LGA, is considered a physical pair: an intermediate
luminosity late type spiral, NGC3447, and an irregular companion, NGC3447A,
linked by a faint filament of matter. A ring-like structure in the NGC3447
outskirts is emphasised by UV observations. This work aims to contribute to the
understanding of galaxy evolution in low density environments, favourable
habitat to highly effective encounters. We performed a multi-wavelength
analysis of the surface photometry of this system to derive spectral energy
distribution and structural properties using UV and optical images. We also
characterised the velocity field of the pair using new kinematic observations.
All these data are used to constrain smooth particle hydrodynamic simulations
with chemo-photometric implementation to shed light on the evolution of this
system. Luminosity profiles are all consistent with the presence of a disc
extending and including NGC3447A. The overall velocity field does not emphasise
any significant rotation pattern, rather a small velocity gradient between
NGC3447 and NGC3447A. Our simulation, detached from a large grid explored to
best-fit the global properties of the system, suggests that this arises from an
encounter between two halos of equal mass. NGC3447 and NGC3447A belong to the
same halo, NGC3447A being a substructure of the same disk as NGC3447. The halo
gravitational instability, enhanced by the encounter, fuels a long lived
instability in this dark matter dominated disk, driving its morphology. This
system may warn about a new class of "false pairs" and the potential danger of
a misunderstanding of such objects in pair surveys that could produce a severe
underestimate of the total mass of the system. (abridged)
