We present a comprehensive suite of high-resolution ( parsec-scale ) , idealised ( non-cosmological ) galaxy merger simulations ( 24 runs , stellar mass ratio \sim 2.5:1 ) to investigate the connection between interaction-induced star formation and the evolution of the interstellar medium ( ISM ) in various temperature-density regimes .
We use the GIZMO code and the second version of the “ Feedback in Realistic Environments ” model ( FIRE-2 ) , which captures the multi-phase structure of the ISM .
Our simulations are designed to represent galaxy mergers in the local Universe .
In this work , we focus on the ‘ galaxy-pair period ’ between first and second pericentric passage .
We split the ISM into four regimes : hot , warm , cool and cold-dense , motivated by the hot , ionised , atomic and molecular gas phases observed in real galaxies .
We find that , on average , interactions enhance the star formation rate of the pair ( \sim 30 \% , merger-suite sample average ) and elevate their cold-dense gas content ( \sim 18 \% ) .
This is accompanied by a decrease in warm gas ( \sim 11 \% ) , a negligible change in cool gas ( \sim 4 \% increase ) , and a substantial increase in hot gas ( \sim 400 \% ) .
The amount of cold-dense gas with densities above 1000 cm ^ { -3 } ( the cold ultra-dense regime ) is elevated significantly ( \sim 240 \% ) , but only accounts for \sim 0.15 \% ( on average ) of the cold-dense gas budget .