The stellar bar - dark matter halo connection in the TNG50 simulations

Abstract

Stellar bars in disk galaxies grow by losing angular momentum to their environments, including the Dark Matter (DM) halo, stellar and gas disks, and interacting satellite galaxies. This exchange of angular momentum during galaxy evolution hints at a connection between bar properties and the DM halo spin $\lambda$ -- the dimensionless form of DM angular momentum. We investigate the connection of halo spin $\lambda$ and galaxy properties in the presence/absence of stellar bars, using the cosmological magneto-hydrodynamic TNG50 simulations at three redshifts $z_r=0, 0.1$ and 1. We estimate the halo spin for barred and unbarred galaxies (bar strength: $0<A_2/A_0<0.7$) at the central regions of the DM halo close to the galaxy disk and far from the disk, close to halo virial radius. At $z_r=0$, strongly barred galaxies ($A_2/A_0>0.4$) reside in DM halos having low spin and low specific angular momentum, while unbarred and weakly barred galaxies ($A_2/A_0<0.2$) are hosted in high spin and high specific angular momentum halos. The inverse correlation between bar strength and halo spin is surprising since previous studies show that bars transfer angular momentum to DM halos. However, the bar strength-halo spin connection is more complex at higher redshift ($z_r=1$) with higher halo spin for all galaxies than that at $z_r=0$. Using galaxy samples across various DM halo mass ranges, we highlight the importance of sample selection in obtaining meaningful results. Investigating the bar--halo connection in further detail is crucial for understanding the impact of bars on galaxy evolution models.Comment: 20 pages (including Appendix), 12 figures; submitted to AAS Journals; comments are welcome