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 generalise 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.
