The Structural Evolution of Isolated Galaxies at Low Redshift in the IllustrisTNG Simulation.

We study the structural evolution of isolated star-forming galaxies in the Illustris TNG100-1 hydrodynamical simulation, with a focus on investigating the growth of the central core density within 2 kpc ($\Sigma_{*,2kpc}$) in relation to total stellar mass ($M_*$) at z $\sim$ $10^{10} M_{\odot}$) mergers, which are mostly dry. Disc instabilities, as measured by the fraction of mass with Toomre Q $\sim$ $10^{9.5} M_{\odot}$). For massive galaxies the total specific angular momentum of accreting gas is the most important predictor of future core growth. Our results suggest that the angular momentum of accreting gas controls the slope, width and zero-point evolution of the $\Sigma_{*,2kpc}$-$M_*$ relation.