Toward First-Principle Simulations of Galaxy Formation: II. Shock-Induced Starburst at a Collision Interface During the First Encounter of Interacting Galaxies

TL;DR

This study uses high-resolution simulations to show that galaxy collisions naturally induce large-scale starbursts at the collision interface, with gas density PDFs evolving during the encounter, providing insights into starburst phenomena.

Contribution

First-principle high-resolution simulations reveal the natural occurrence of starbursts at galaxy collision interfaces and track the evolution of gas density PDFs during encounters.

Findings

Starburst occurs naturally at the collision interface during first encounter.

Gas density PDF shows a shift to higher densities during starburst.

Post-starburst, the gas PDF returns to a steady state.

Abstract

We investigated the evolution of interacting disk galaxies using high-resolution $N$-body/SPH simulations, taking into account the multiphase nature of the interstellar medium (ISM). In our high-resolution simulations, a large-scale starburst occurred naturally at the collision interface between two gas disks at the first encounter, resulting in the formation of star clusters. This is consistent with observations of interacting galaxies. The probability distribution function (PDF) of gas density showed clear change during the galaxy-galaxy encounter. The compression of gas at the collision interface between the gas disks first appears as an excess at $n_{\rm H} \sim 10{\rm cm^{-3}}$ in the PDF, and then the excess moves to higher densities ($n_{\rm H} \gtrsim 100{\rm cm^{-3}}$) in a few times $10^7$ years where starburst takes place. After the starburst, the PDF goes back to the quasi-steady state. These results give a simple picture of starburst phenomena in galaxy-galaxy encounters.