Formation of a Malin 1 analogue in IllustrisTNG by stimulated accretion

TL;DR

This study identifies a Malin 1-like galaxy in the IllustrisTNG simulation, demonstrating its formation through hot halo gas cooling triggered by galaxy mergers, aligning well with observed features.

Contribution

It presents the first simulated Malin 1 analogue and reveals a new formation pathway involving stimulated accretion from hot halo gas.

Findings

Simulated galaxy matches observed properties of Malin 1.

Large cold gas disk formed via hot halo gas cooling.

Galaxy formation via stimulated accretion is a viable pathway.

Abstract

The galaxy Malin 1 contains the largest stellar disk known but the formation mechanism of this structure has been elusive. In this paper, we report a Malin 1 analogue in the 100 Mpc IllustrisTNG simulation and describe its formation history. At redshift zero, this massive galaxy, having a maximum circular velocity $V_{\rm max}$ of 430 ${\rm km\ s^{-1}}$, contains a 100 kpc gas/stellar disk with morphology similar to Malin 1. The simulated galaxy reproduces well many observed features of Malin 1's vast disk, including its stellar ages, metallicities, and gas rotation curve. We trace the extended disk back in time and find that a large fraction of the cold gas at redshift zero originated from the cooling of hot halo gas, triggered by the merger of a pair of intruding galaxies. Our finding provides a novel way to form large galaxy disks as extreme as Malin 1 within the current galaxy formation framework.