  We present novel insights into the interplay between tidal forces and star
formation in interacting galaxies before their first pericentre passage. We
investigate seven close pair galaxies devoid of visible tidal disturbances,
such as tails, bridges, and shells. Using integral field spectroscopy (IFS)
data of extended Calar Alto Legacy Integral Field Area (eCALIFA), we unveil a
previously unreported phenomenon: H alhpa emission, a proxy for recent star
formation, exhibits a significant enhancement in regions facing the companion
galaxy, reaching up to 1.9 times higher flux compared to opposite directions.
Notably, fainter companions within pairs display a more pronounced one-sided H
alpha excess, exceeding the typical range observed in isolated galaxies with 2
sigma confidence level. Furthermore, the observed H alpha excess in fainter
companion galaxies exhibits a heightened prominence at the outer galactic
regions. These findings suggest that tidal forces generated before the first
pericentre passage exert a stronger influence on fainter galaxies due to their
shallower potential wells by their brighter companions. This unveils a more
intricate interplay between gravitational interactions and star formation
history within interacting galaxies than previously understood, highlighting
the need further to explore the early stages of interaction in galaxy
evolution.
