  A detailed study of the morphology of lenticular galaxies is an important way
to understand how this type of galaxy formed and evolves over time. Decomposing
a galaxy into its components (disc, bulge, bar, ...) allows recovering the
colour gradients present in each system, its star formation history, and its
assembly history. We use GALFITM to perform a multi-wavelength structural
decomposition of the closest lenticular galaxy, NGC 3115, resulting in the
description of its stellar light into several main components: a bulge, a thin
disc, a thick disc and also evidence of a bar. We report the finding of central
bluer stellar populations in the bulge, as compared to the colour of the galaxy
outskirts, indicating either the presence of an Active Galactic Nucleus (AGN)
and/or recent star formation activity. From the spectral energy distribution
results, we show that the galaxy has a low luminosity AGN component, but even
excluding the effect of the nuclear activity, the bulge is still bluer than the
outer-regions of the galaxy, revealing a recent episode of star formation.
Based on all of the derived properties, we propose a scenario for the formation
of NGC 3115 consisting of an initial gas-rich merger, followed by accretions
and feedback that quench the galaxy, until a recent encounter with the
companion KK084 that reignited the star formation in the bulge, provoked a core
displacement in NGC 3115 and generated spiral-like features. This result is
consistent with the two-phase formation scenario, proposed in previous studies
of this galaxy.
