WALLABY Pilot Survey: Star Formation Enhancement and Suppression in Gas-rich Galaxy Pairs

Abstract

Galaxy interactions can significantly affect the star formation in galaxies, but it remains a challenge to achieve a consensus on the star formation rate (SFR) enhancement in galaxy pairs. Here, we investigate the SFR enhancement of gas-rich galaxy pairs detected by the Widefield ASKAP L-band Legacy All-sky Blind surveY. We construct a sample of 278 paired galaxies spanning a stellar mass (M _*) range from 10^7.6 to 10^11.2 M _⊙. We obtain individual masses of atomic hydrogen (H I) for these paired galaxies using a novel deblending algorithm for H I data cubes. Quantifying the interaction stages and strengths with parameters motivated by first-principles analysis, we find that, at fixed stellar and H I mass, the alteration in the SFR of galaxy pairs starts when their dark matter halos are encountered. For galaxies with a stellar mass lower than 10⁹ M _⊙, their SFRs show tentative suppression of 1.4σ after the halo encounter, and then become enhanced when their H I disks overlap, regardless of mass ratios. In contrast, the SFRs of galaxies with M _* > 10⁹ M _⊙ increase monotonically toward smaller projected distances and radial velocity offsets. When a close companion is present, a pronounced SFR enhancement is found for the most H I-poor high-mass galaxies in our sample. Collecting the observational evidence, we provide a coherent picture of the evolution of galaxy pairs and discuss how the tidal effects and hydrodynamic processes shape the SFR enhancement. Our results provide a coherent picture of gas-rich galaxy interactions and impose constraints on the underlying physical processes.