Massive Low Surface Brightness Galaxies in the EAGLE Simulation

TL;DR

This study uses the EAGLE simulation to explore the formation, properties, and environmental factors of low surface brightness galaxies, revealing their connection to high angular momentum, low star formation, and merger history.

Contribution

It provides new insights into the formation mechanisms and environmental dependence of LSBGs, especially highlighting the role of angular momentum and mergers in their development.

Findings

LSBGs are more isolated than HSBGs, mainly because they are less likely to be close satellites.

High angular momentum and recent star formation from co-rotating gas are key to LSBG formation.

Extended LSBGs in EAGLE form through mergers and inhabit high-spin dark matter halos.

Abstract

We investigate the formation and properties of low surface brightness galaxies (LSBGs) with $M_{*} > 10^{9.5} \mathrm{M_{\odot}}$ in the EAGLE hydrodynamical cosmological simulation. Galaxy surface brightness depends on a combination of stellar mass surface density and mass-to-light ratio ($M/L$), such that low surface brightness is strongly correlated with both galaxy angular momentum (low surface density) and low specific star formation rate (high $M/L$). This drives most of the other observed correlations between surface brightness and galaxy properties, such as the fact that most LSBGs have low metallicity. We find that LSBGs are more isolated than high surface brightness galaxies (HSBGs), in agreement with observations, but that this trend is driven entirely by the fact that LSBGs are unlikely to be close-in satellites. The majority of LSBGs are consistent with a formation scenario in which the galaxies with the highest angular momentum are those that formed most of their stars recently from a gas reservoir co-rotating with a high-spin dark matter halo. However, the most extended LSBG disks in EAGLE, which are comparable in size to observed giant LSBGs, are built up via mergers. These galaxies are found to inhabit dark matter halos with a higher spin in their inner regions ($<0.1r_{200c}$), even when excluding the effects of baryonic physics by considering matching halos from a dark matter only simulation with identical initial conditions.