The Effect of Galaxy Interactions on Starbursts in Milky Way-Mass Galaxies in FIRE Simulations

TL;DR

This study uses FIRE-2 simulations to investigate how galaxy interactions influence starbursts in Milky Way-mass galaxies, finding that only some major interactions trigger starbursts and most are unrelated to interactions.

Contribution

It provides new insights into the specific conditions under which galaxy interactions induce starbursts in Milky Way-mass galaxies, highlighting that most starbursts are not caused by interactions.

Findings

Positive correlation between torque and SFR in near-equal-mass interactions at certain redshifts

Most starbursts occur independently of galaxy interactions

Transition from bursty to steady star formation is interaction-independent

Abstract

Simulations and observations suggest that galaxy interactions may enhance the star formation rate (SFR) in merging galaxies. One proposed mechanism is the torque exerted on the gas and stars in the larger galaxy by the smaller galaxy. We analyze the interaction torques and star formation activity on six galaxies from the FIRE-2 simulation suite with masses comparable to the Milky Way galaxy at redshift $z=0$. We trace the halos from $z = 3.6$ to $z=0$, calculating the torque exerted by the nearby galaxies on the gas in the central galaxy. We calculate the correlation between the torque and the SFR across the simulations for various mass ratios. For near-equal-stellar-mass-ratio interactions in the galaxy sample, occurring between $z=1.2-3.6$, there is a positive and statistically significant correlation between the torque from nearby galaxies on the gas of the central galaxies and the SFR. For all other samples, no statistically significant correlation is found between the torque and the SFR. Our analysis shows that some, but not all, major interactions cause starbursts in the simulated Milky Way-mass galaxies, and that most starbursts are not caused by galaxy interactions. The transition from `bursty' at high redshift ($z\gtrsim1$) to `steady' star-formation state at later times is independent of the interaction history of the galaxies, and most of the interactions do not leave significant imprints on the overall trend of the star formation history of the galaxies.