Galactic angular momentum in the IllustrisTNG simulation - I. Connection to morphology, halo spin, and black hole mass

We use the TNG100 simulation of the IllustrisTNG project to investigate the stellar specific angular momenta (j(*)) of similar to 12 000 central galaxies at z = 0 in a full cosmological context, with stellar masses (M-*) ranging from 10(9) to 10(12) M-circle dot. We find that the j(*)-M-* relations for early-type and late-type galaxies in IllustrisTNG are in good overall agreement with observations, and that these galaxy types typically 'retain' similar to 10-20 and similar to 50-60 per cent of their host haloes' specific angular momenta, respectively, with some dependence on the methodology used to measure galaxy morphology. We present results for kinematic as well as visual-like morphological measurements of the simulated galaxies. Next, we explore the scatter in the j(*)-M-* relation with respect to the spin of the dark matter halo and the mass of the supermassive black hole (BH) at the galactic centre. We find that galaxies residing in faster spinning haloes, as well as those hosting less massive BHs, tend to have a higher specific angular momentum. We also find that, at fixed galaxy or halo mass, halo spin and BH mass are anticorrelated with each other, probably as a consequence of more efficient gas flow towards the galactic centre in slowly rotating systems. Finally, we show that halo spin plays an important role in determining galaxy sizes - larger discs form at the centres of faster rotating haloes - although the trend breaks down for massive galaxies with M-* greater than or similar to 10(11) M-circle dot, roughly the mass scale at which a galaxy's stellar mass becomes dominated by accreted stars.

Automated summary

This article uses the TNG100 simulation of the IllustrisTNG project to investigate the stellar specific angular momenta (j(*)) of approximately 12,000 central galaxies at z = 0 in a cosmological context. The results show that the j(*)-M-* relations for early-type and late-type galaxies in IllustrisTNG are in good agreement with observations, and that the specific angular momenta retained by these galaxy types are approximately 10-20% and 50-60% of their host haloes, respectively, with some dependence on the methodology used to measure galaxy morphology. The article also explores the scatter in the j(*)-M-* relation with respect to the spin of the dark matter halo and the mass of the supermassive black hole (BH) at the galactic centre. The findings indicate that galaxies in faster spinning haloes and those hosting less massive BHs tend to have higher specific angular momentum. The article further reveals that, at fixed galaxy or halo mass, halo spin and BH mass are anticorrelated, possibly due to more efficient gas flow towards the galactic centre in slowly rotating systems. Finally, the article demonstrates the importance of halo spin in determining galaxy sizes, with larger discs forming at the centres of faster rotating haloes, though this trend breaks down for massive galaxies with stellar masses dominated by accreted stars at approximately 10^11 M-circle dot.