Abstract
Galaxy groups are more than an intermediate scale between clusters and halos hosting individual galaxies, they are crucial laboratories capable of testing a range of astrophysics from how galaxies form and evolve to large scale structure (LSS) statistics for cosmology. Cosmological hydrodynamic simulations of groups on various scales offer an unparalleled testing ground for astrophysical theories. Widely used cosmological simulations with ∼(100 Mpc)3 volumes contain statistical samples of groups that provide important tests of galaxy evolution influenced by environmental processes. Larger volumes capable of reproducing LSS while following the redistribution of baryons by cooling and feedback are the essential tools necessary to constrain cosmological parameters. Higher resolution simulations can currently model satellite interactions, the processing of cool (T≈104−5 K) multi-phase gas, and non-thermal physics including turbulence, magnetic fields and cosmic ray transport. We review simulation results regarding the gas and stellar contents of groups, cooling flows and the relation to the central galaxy, the formation and processing of multi-phase gas, satellite interactions with the intragroup medium, and the impact of groups for cosmological parameter estimation. Cosmological simulations provide evolutionarily consistent predictions of these observationally difficult-to-define objects, and have untapped potential to accurately model their gaseous, stellar and dark matter distributions.
Highlights
Galaxy groups are versatile laboratories to study a range of astrophysics spanning nongravitational, baryonic processes associated with galaxy formation to large-scale structure statistics constraining cosmology
The temperature, density, and metallicity of their gaseous baryons can be probed via soft X-ray emission without stacking, while their shallower gravitational potential wells relative to clusters allow energetic feedback to remove a significant fraction of baryons
While Gonzalez et al [205] measured that the integrated group stellar masses from the BGG, the intragroup light (IGrL), and satellite galaxies could account for the missing gaseous baryon resulting in a groups retaining all baryons inside R500, this was later challenged
Summary
Galaxy groups are versatile laboratories to study a range of astrophysics spanning nongravitational, baryonic processes associated with galaxy formation to large-scale structure statistics constraining cosmology. We define these masses as M∆, the sum of all matter species (i.e., dark matter and baryons) within a spherical aperture r∆ inside which the mean density equals ∆ times the critical density of the universe; we adopt the value ∆ = 500 as commonly used in X-ray studies of the IGrM/ICM and define a group halo as one with M500(c) = 1013–1014 M (r500(c) ≈ 340–600 kpc) 1. This definition places groups between lower-mass galactic halos (M500 1013 M ) and more massive clusters (M500 1014 M ).
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