Enhanced Star Formation and Black Hole Accretion Rates in Galaxy Mergers in IllustrisTNG50

TL;DR

This study uses the IllustrisTNG50 simulation to analyze how galaxy mergers influence star formation and black hole growth across different cosmic epochs, revealing persistent enhancements post-merger and their dependence on various factors.

Contribution

It provides the first detailed analysis of merger effects on star formation and black hole activity in the high-resolution TNG50 simulation across a broad redshift range.

Findings

Mergers increase specific star formation rates at z ≤ 3.

Mergers enhance black hole accretion rates at z ≲ 2.

Enhancements last for at least ~1 Gyr after mergers.

Abstract

Many theoretical and observational studies have suggested that galaxy mergers may trigger enhanced star formation or active galactic nuclei (AGN) activity. We present an analysis of merging and nonmerging galaxies from $0.2 \leq z \leq 3$ in the IllustrisTNG50 simulation. These galaxies encompass a range of masses ($M_\star > 10^{8}M_\odot$), multiple merger stages, and mass ratios ($\geq1:10$). We examine the effect that galaxy mergers have on star formation and black hole accretion rates in the TNG50 universe. We additionally investigate how galaxy and black hole mass, merger stage, merger mass ratio, and redshift affect these quantities. Mergers in our sample show excess specific star formation rates (sSFR) at $z \leq 3$ and enhanced specific black hole accretion rates (sBHAR) at $z \lesssim 2$. The difference between sSFRs and sBHARs in the merging sample compared to the non-merging sample increases as redshift decreases. Additionally, we show that these enhancements persist for at least $\sim1$ Gyr after the merger event. Investigating how mergers behave in the TNG50 simulation throughout cosmic time enables both a better appreciation of the importance of spatial resolution in cosmological simulations and a better basis to understand our high-$z$ universe with observations from $\textit{JWST}$.