Exploring the Impact of Galactic Interactions and Mergers on the Central Star Formation of APEX/EDGE–CALIFA Galaxies

Galactic interactions and subsequent mergers are a paramount channel for galaxy evolution. In this work, we use the data from 236 star-forming CALIFA galaxies with integrated molecular gas observations in their central region (approximately within an effective radius)—from the APEX millimeter telescope and the CARMA millimeter telescope array. This sample includes isolated (126 galaxies) and interacting galaxies in different merging stages (110 galaxies; from pairs, merging, and postmerger galaxies). We show that the impact of interactions and mergers in the center of galaxies is revealed as an increase in the fraction of molecular gas (compared to isolated galaxies). Furthermore, our results suggest that the change in star formation efficiency is the main driver for both an enhancement and/or suppression of the central star formation—except in merging galaxies where the enhanced star formation appears to be driven by an increase of molecular gas. We suggest that gravitational torques due to the interaction and subsequent merger transport cold molecular gas inwards, increasing the gas fraction without necessarily increasing star formation.