In cosmology and astrophysics, the term "halo virial radius" refers to the characteristic size of a dark matter halo, which is a huge, roughly spherical region of space that surrounds galaxies and galaxy clusters. Dark matter halos are theorized to emerge by gravitational collapse of minor changes in matter density in the early cosmos.
Dark matter halos are vast, gravitationally bound regions of space where dark matter, a mysterious and invisible substance, is concentrated. These halos encircle galaxies and galaxy clusters, providing the gravitational framework that shapes the universe on a grand scale. Dark matter halos are essential in understanding the formation and evolution of galaxies, as they influence the distribution and dynamics of ordinary matter, such as stars and gas, through their gravitational pull. While dark matter itself cannot be directly observed, its presence is inferred from its gravitational effects on visible matter and light.
The virial radius marks the boundary beyond which the dark matter halo's gravitational influence becomes negligible compared to that of surrounding structures. Inside this radius, the gravitational pull of the dark matter dominates, contributing to the dynamics of galaxies and galaxy clusters. Beyond the virial radius (𝑅200c), the gravitational pull of the DM halo is no longer significant in relation to the surrounding structures. The motions of galaxies and galaxy clusters are influenced by the gravitational attraction of DM within this radius.
The virial radius (𝑅200c) is the radius at which the average density of the dark matter (DM) halo is 200 times the critical density of the universe at the present time.
The large-scale correlation between the star formation of neighboring galaxies beyond the halo virial radius indicates the importance of environmental processes in regulating galaxy evolution on a cosmic scale. Gas stripping, tidal interactions, mergers, and the influence of the cosmic web all contribute to shaping the star formation histories of galaxies in the vast cosmic web environment.
Gas stripping, where gas is removed from galaxies due to interactions with their surroundings, plays a significant role. Beyond the halo boundary, galaxies are still subject to the influence of the surrounding environment, including intracluster or intragroup gas, tidal forces, and interactions with neighboring galaxies. These environmental effects can strip gas from galaxies, affecting their ability to form stars. In regions beyond the halo boundary, galaxies may experience galactic winds induced by the hot intracluster or intragroup medium. These processes can remove gas from galaxies, quenching their star formation activity. Additionally, interactions between galaxies and the intracluster medium can compress gas, triggering star formation in some regions while suppressing it in others. Beyond the halo virial radius, galaxies can experience tidal interactions and mergers with neighboring galaxies. These interactions can trigger bursts of star formation in some galaxies while disrupting the gas reservoirs of others, leading to variations in star formation activity on large scales.
Link 🔗: Research Paper