Star formation triggered by galaxy interactions in modified gravity

Together with interstellar turbulence, gravitation is one key player in star formation. It acts both at galactic scales in the assembly of gas into dense clouds and inside those structures for their collapse and the formation of pre-stellar cores. To understand to what extent the large-scale dynamics govern the star formation activity of galaxies, we present hydrodynamical simulations in which we generalize the behaviour of gravity to make it differ from Newtonian dynamics in the low-acceleration regime. We focus on the extreme cases of interacting galaxies, and compare the evolution of galaxy pairs in the dark matter paradigm to that in the Milgromian dynamics (MOND) framework. Following up on the seminal work by Tiret & Combes, this paper documents the first simulations of galaxy encounters in MOND with a detailed Eulerian hydrodynamical treatment of baryonic physics, including star formation and stellar feedback. We show that similar morphologies of the interacting systems can be produced by both the dark matter and MOND formalisms, but require a much slower orbital velocity in the MOND case. Furthermore, we find that the star formation activity and history are significantly more extended in space and time in MOND interactions, in particular in the tidal debris. Such differences could be used as observational diagnostics and make interacting galaxies prime objects in the study of the nature of gravitation at galactic scales.