Spin speed correlations and the evolution of galaxy-halo systems
Galaxy angular momenta (spins) contain valuable cosmological information, complementing their positions and velocities. The baryonic spin direction of galaxies has been probed as a reliable tracer of their host halos and the primordial spin modes. Here we use the TNG100 simulation of the IllustrisTNG project to study the spin magnitude correlations between dark matter, gas, and stellar components of galaxy-halo systems and their evolutions across cosmic history. We find that these components generate similar initial spin magnitudes from the same tidal torque in Lagrangian space. At low redshifts, the gas component still traces the spin magnitude of the dark matter halo and the primordial spin magnitude. However, the traceability of the stellar component depends on the $ex$ $situ$ stellar mass fraction, $f_{\rm acc}$. Our results suggest that the galaxy baryonic spin magnitude can also serve as a tracer of their host halo and the initial perturbations, and the galaxy-halo correlations are affected by the similarity of their evolution histories.