The formation and evolution of Supermassive disks in IllustrisTNG

Abstract

Supermassive disks are outstanding galaxies whose formation and evolution are still poorly understood. They comprise a large variety of objects, ranging from large, low-surface-brightness galaxies, such as Malin 1, to the most spectacular superluminous spirals. However, we still do not know the physical mechanisms behind its formation, and whether they will be long-lived objects or whether their mass could destroy them in time. We aim to investigate the formation and evolution of these galaxies using the magnetohydrodynamical state-of-the-art simulation IllustrisTNG-100. We defined supermassive disks as galaxies with $\lambda / \sqrt{\varepsilon} \geq 0.31$ or 0.71, and with stellar mass log$_{10}M_\star/M_\odot > 10^{11}$. We studied the color, merging history, AGN history, and environment in which these galaxies reside. Supermassive disk galaxies typically experience a quiescent merging history, with $48\%$ experiencing no significant mergers at $z \leq 1$. Their stellar mass growth is driven mainly by star formation, unlike spheroidal galaxies, which require a significant number of mergers to form. Moreover, the mergers experienced by disk galaxies are generally rich in gas content, irrespective of whether they are minor or major events. Supermassive disks exist across various environments, from isolation to clusters, with $\sim 60\%$ inhabiting in isolation or low-mass groups, $\sim 25\%$ residing in massive groups, and $\sim15\%$ residing within galaxy clusters. When studying the evolution of supermassive disks selected at $z=0.5$, we show that when they gain sufficient mass, the probability of them maintaining their disk-like structure up to $z=0$ is relatively high ($\sim 60\%$). Lastly, while AGN significantly influences the regulation of star formation in galaxies, it does not directly alter their morphological structure.