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Recent observations have shown that the majority of the Andromeda galaxys satellites are aligned in a thin plane. On the theoretical side it has been proposed that galaxies acquire their gas via cold streams. In addition, numerical simulations show that the same streams also deliver gas clumps which could potentially develop into satellite galaxies. Assuming that cold streams are a major source of satellite systems around galaxies we calculate the probabilities in two different models to find a certain fraction of satellites within a thin plane around the central galaxy of the host halo with and without having the same sense of rotation. Using simple geometrical considerations and adopting a random orientation of the streams we demonstrate that the vast thin disk of satellites detected around Andromeda can naturally be explained within this framework. In fact, without any satellite scattering, two streams would lead to too many satellites in the thin plane, compared with the observations. Three streams reproduce the observations very well. Natural implications from our model are that all massive galaxies should have a thin plane of satellites and that the satellites should naturally distribute themselves not only into a single plane but into several inclined ones. We estimate the effect of additional satellites accreted from random directions and find it to be of minor relevance for a mild inflow of satellites from random directions.
{Abridged} We investigate the observability of cold accretion streams at redshift 3 via Lyman-alpha (Lya) emission and the feasibility of cold accretion as the main driver of Lya blobs (LABs). We run cosmological zoom simulations focusing on 3 halos
Within the Cold Dark Matter scenario the hierarchical merging paradigm is the natural result to form massive galactic halos by the minor mergers of sub-halos and, by this, inherently their stellar halo. Although this must be also invoked for the Milk
Disk galaxies at high redshift have been predicted to maintain high gas surface densities due to continuous feeding by intense cold streams leading to violent gravitational instability, transient features and giant clumps. Gravitational torques betwe
We present results from high--resolution cosmological hydrodynamical simulations of a Milky--Way-sized halo, aimed at studying the effect of feedback on the nature of gas accretion. Simulations include a model of inter-stellar medium and star formati
Understanding the evolution of accretion activity is fundamental to our understanding of how galaxies form and evolve over the history of the Universe. We analyse a complete sample of 27 radio galaxies which includes both high-excitation (HEGs) and l