(In)stability of cold streams feeding massive galaxies at high redshift
Massive star-forming galaxies at redshift z~1-4, during the most active phase of galaxy formation, were fed by cold streams of dense gas flowing along the filaments of the cosmic web. These streams penetrate through the hot halo, encompassed by a stable shock at the virial radius, and make their way towards the central galaxy with Mach numbers of 10 or larger. On their way, they are subject to numerous instabilities which can affect their morphology and lead to the emission of observable radiation. I will discuss the evolution of cold supersonic streams in hot halos, using both analytic toy models and idealized simulations. Unlike current cosmological simulations, these simulations resolve the streams with several hundred resolution elements and capture the detailed evolution of the instability. For a large region of the streams’ parameter space, compressible Kelvin-Helmholtz instabilities can lead to disruption in less than a virial crossing time. I will discuss the linear and non-linear phases of the hydro-instability. I will also introduce ongoing work aimed at systematically studying the influence of additional physics on stream evolution.