One-sided H alpha Excess before the First Pericentre Passage in Galaxy Pairs

TL;DR

This study reveals that in galaxy pairs without visible tidal features, the galaxy facing its companion shows enhanced H alpha emission indicating increased star formation, especially in fainter galaxies, before their first close approach.

Contribution

It uncovers a previously unreported one-sided H alpha excess in galaxy pairs prior to first pericentre, highlighting early tidal effects on star formation in faint galaxies.

Findings

H alpha emission is significantly higher on the facing side of galaxy pairs.

Fainter companion galaxies show more pronounced H alpha excess.

Outer regions of faint galaxies exhibit stronger H alpha enhancement.

Abstract

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.