Two interacting galaxies hiding as one, revealed by MaNGA
  Given their prominent role in galaxy evolution, it is of paramount importance
to unveil galaxy interactions and merger events and to investigate the
underlying mechanisms. The use of high-resolution data makes it easier to
identify merging systems, but it can still be challenging when the morphology
does not show any clear galaxy-pair or gas bridge. Characterising the origin of
puzzling kinematic features can help to reveal complicated systems. Here, we
present a merging galaxy, MaNGA 1-114955, in which we highlighted the
superimposition of two distinct rotating discs along the line of sight. These
counter-rotating objects both lie on the star-forming main sequence but display
perturbed stellar velocity dispersions. The main galaxy presents off-centred
star formation as well as off-centred high-metallicity regions supporting the
scenario of recent starbursts, while the secondary galaxy hosts a central
starburst which coincides with an extended radio emission, in excess with
respect to star formation expectations. Stellar mass as well as dynamical mass
estimates agree towards a mass ratio within the visible radius of 9:1 for these
interacting galaxies. We suggest we are observing a pre-coalescence stage of a
merger. The primary galaxy has accreted gas through a past first pericentre
passage about 1 Gyr ago, and more recently from the secondary gas-rich galaxy,
which exhibits an underlying active galactic nucleus (AGN). Our results
demonstrate how a galaxy can hide another one and the relevance of a
multi-component approach to study ambiguous systems. We anticipate our method
to be efficient at unveiling the mechanisms taking place in a sub-sample of
galaxies observed by the Mapping Nearby Galaxies at Apache Point Observatory
(MaNGA) survey, all exhibiting kinematic features of puzzling origin in their
gas emission lines.
