The effect of galaxy mass ratio on merger--driven starbursts

TL;DR

This study uses numerical simulations to investigate how galaxy mass ratio influences merger-driven starbursts, revealing that star formation is highly dependent on mass ratio and galaxy structure, with feedback processes affecting burst efficiency.

Contribution

It provides new insights into the dependence of starburst efficiency on galaxy mass ratio, structure, and orbit, using advanced simulations with improved feedback modeling.

Findings

Star formation strongly depends on galaxy mass ratio.

Presence of a stellar bulge suppresses starbursts in large mass ratio mergers.

Compact gas distribution and higher gas fractions decrease burst efficiency.

Abstract

We employ numerical simulations of galaxy mergers to explore the effect of galaxy mass ratio on merger--driven starbursts. Our numerical simulations include radiative cooling of gas, star formation, and stellar feedback to follow the interaction and merger of four disk galaxies. The galaxy models span a factor of 23 in total mass and are designed to be representative of typical galaxies in the local Universe. We find that the merger--driven star formation is a strong function of merger mass ratio, with very little, if any, induced star formation for large mass ratio mergers. We define a burst efficiency that is useful to characterize the merger--driven star formation and test that it is insensitive to uncertainties in the feedback parameterization. In accord with previous work we find that the burst efficiency depends on the structure of the primary galaxy. In particular, the presence of a massive stellar bulge stabilizes the disk and suppresses merger--driven star formation for large mass ratio mergers. Direct, co--planar merging orbits produce the largest tidal disturbance and yield that most intense burst of star formation. Contrary to naive expectations, a more compact distribution of gas or an increased gas fraction both decrease the burst efficiency. Owing to the efficient feedback model and the newer version of SPH employed here, the burst efficiencies of the mergers presented here are smaller than in previous studies.