NIHAO-RiNG: A Comparison of Simulated Disk Galaxies from GASOLINE and GIZMO

Abstract We utilize the publicly available code GIZMO to re-simulate 12 galaxies selected from the Numerical Investigation of a Hundred Astronomical Object (NIHAO) simulation suite, which were run with the GASOLINE code, then compare their properties. We find that while both codes with the same initial conditions and large-scale environments can successfully produce similar galactic disks in Milky Way-mass systems, yet significant differences are still seen in many aspects, particularly the circumgalactic medium (CGM) environment they reside in. Specifically, the thermal feedback recipe used in GASOLINE results in ubiquitous, long-term, large-scale outflows, primarily driven by high-density hot interstellar medium from the galaxy center, preventing the intergalactic medium from falling efficiently. Recycled gas and inflows in the CGM appear at 10 4∼5 K, playing a crucial role in the formation of cold disks in the NIHAO simulations. In contrast, disk galaxies simulated by GIZMO do not exhibit prominent outflows at low redshifts, but instead display quasi-virialized hot gas halos that arise from the interaction between inflows and feedback-driven outflows. Therefore, the origins of mass and angular momentum of the cold disk in the two simulations are quite different, even though the final morphologies of the corresponding galaxies are both disky. The differences in the distribution of CGM gas are mainly due to different feedback models implemented in the two codes. Future observations of CGM could provide valuable insight into the physics governing the baryon cycle in galaxies.