Properties of Voids and Void Galaxies in the TNG300 Simulation

Abstract

We investigate the properties of voids and void galaxies in the TNG300 simulation. Using a luminous galaxy catalog and a spherical void-finding algorithm, we identify 5078 voids at redshift z = 0. The voids cover 83% of the simulation volume and have a median radius of 4.4 h −1 Mpc. We identify two populations of field galaxies based on whether the galaxies reside within a void (“void galaxies”; 75,220 objects) or outside a void (“nonvoid galaxies”; 527,454 objects). Within the voids, mass does not directly trace light. Instead, the mean radial underdensity profile as defined by the locations of void galaxies is systematically lower than the mean radial underdensity profile as defined by the dark matter (i.e., the voids are more “devoid” of galaxies than they are of mass). Within the voids, the integrated underdensity profiles of the dark matter and the galaxies are independent of the local background density (i.e., voids-in-voids versus voids-in-clouds). Beyond the void radii, however, the integrated underdensity profiles of both the dark matter and the galaxies exhibit strong dependencies on the local background density. Compared to nonvoid galaxies, void galaxies are on average younger, less massive, bluer in color, less metal enriched, and have smaller radii. In addition, the specific star formation rates of void galaxies are ∼20% higher than nonvoid galaxies and, in the case of galaxies with central supermassive black holes with M BH ≳ 3 × 106 h −1 M ⊙, the fraction of active void galaxies is ∼25% higher than active nonvoid galaxies.

Cosmology from One Galaxy in a Void?

“…This is an important and new result that may shed light on the impact of baryonic processes on galaxy formation and evolution as a function of the cosmic environment. Recent works showing that void galaxies have distinct characteristics in the IllustrisTNG simulation (Rodríguez-Medrano et al 2024; Curtis et al 2024) could hint to an explanation for our results. We also show that the improvement obtained when using void galaxies is more significant when a more stringent selection is considered, robustly selecting according to both the large-scale and local environments.…”

“…Still, due to their isolated nature, it is reasonable to expect that void galaxies -less influenced by external disturbances such as stripping and harassment-could have a stronger connection to cosmology and the physics of the early universe. In addition, differences have also been investigated specifically in the IllustrisTNG simulations recently: Rodríguez-Medrano et al (2024) and Curtis et al (2024) suggested that void galaxies have significantly different properties compared to nonvoid galaxies, which may impact the link to cosmological information.…”