Astro Lunch

Formation of a Malin1–like galaxy in IllustrisTNG by stimulated accretion

The galaxy Malin 1 contains the largest known spiral structure (over 100 kpc in radius), at least five times larger than the Milky Way. Over the past few years, we have witnessed significant progress in the formation of extended and thin stellar disk with hydrodynamic simulations. Still, it remains a great challenge to understand the physical process behind a disk of this extreme size. In this talk, I will discuss a Malin 1–like galaxy from the 100 Mpc IllustrisTNG cosmological hydrodynamic simulation. At redshift zero, this massive galaxy, having a maximum circular velocity of 430 km/s, contains a ∼100 kpc gas/stellar disk with morphology similar to Malin 1. The simulated galaxy well reproduces many observed features of Malin 1’s vast disk, including stellar ages, metallicities and gas rotation curve. We trace the extended disk back in time and find a large fraction of the cold gas at redshift zero originated from the cooling of hot halo gas, stimulated by a merger of a pair of intruding galaxies.