This paper explores the mapping between the observable properties of a stellar halo in phase- and abundance-space and the parent galaxy's accretion history in terms of the characteristic epoch of accretion and mass and orbits of progenitor objects. The study utilizes a suite of eleven stellar halo models constructed within the context of a standard LCDM cosmology. The results demonstrate that coordinate-space studies are sensitive to the recent (0-8 Gyears ago) merger histories of galaxies (this timescale corresponds to the last few to tens of percent of mass accretion for a Milky-Way-type galaxy). Specifically, the {\it frequency, sky coverage} and {\it fraction of stars} in substructures in the stellar halo as a function of surface brightness are indicators of the importance of recent merging and of the luminosity function of infalling dwarfs. The {\it morphology} of features serves as a guide to the orbital distribution of those dwarfs. Constraints on the earlier merger history (> 8 Gyears ago) can be gleaned from the abundance patterns in halo stars: within our models, dramatic differences in the dominant epoch of accretion or luminosity function of progenitor objects leave clear signatures in the [alpha/Fe] and [Fe/H] distributions of the stellar halo - halos dominated by very early accretion have higher average [alpha/Fe], while those dominated by high luminosity satellites have higher [Fe/H]. This intuition can be applied to reconstruct much about the merger histories of nearby galaxies from current and future data sets.

We use a large suite of carefully controlled full hydrodynamic simulations to study the ram pressure stripping of the hot gaseous haloes of galaxies

We use the galaxy stellar mass and halo merger tree information from the semi-analytic model galaxy catalogue of Font et al. to examine the accretion

In the local Universe, galaxies in groups and clusters contain less gas and are less likely to be forming stars than their field counterparts. This effect is not limited to the central group/cluster regions, but is shown by recent observations to persist out to several virial radii. To gain insight into the extent and cause of this large-scale environmental influence, we use a suite of high-resolution cosmological hydrodynamic simulations to analyse galaxies around simulated groups and clusters of a wide range of mass (log ₁₀M_host/M_⊙ = [13.0, 15.2]). In qualitative agreement with the observations, we find a systematic depletion of both hot and cold gas and a decline in the star-forming fraction of galaxies as far out as ∼5r₂₀₀ from the host centre. A substantial fraction of these galaxies are on highly elliptical orbits and are not infalling for the first time (∼50 per cent at 2r₂₀₀, independent of host mass) or are affected by ‘pre-processing’ (less than 10 per cent of galaxies around groups, increasing to ∼50 per cent near a massive cluster), even a combination of these indirect mechanisms does not fully account for the environmental influence, particularly in the case of the hot gas content. Direct ram pressure interaction with an extended gas ‘halo’ surrounding groups and clusters is shown to be sufficiently strong to strip the hot gas atmospheres of infalling galaxies out to ∼5r₂₀₀. We show that this influence is highly anisotropic, with ram pressure along filaments enhanced by up to a factor of 100 despite significant co-flow of gas and galaxies.

We use the Galaxies-Intergalactic Medium Interaction Calculation (gimic) suite of cosmological hydrodynamical simulations to study the formation of s

Current models of galaxy formation predict satellite galaxies in groups and clusters that are redder than observed. We investigate the effect on the