Early Massive Galaxy Formation by Cold Streams Through Hot Haloes
Aug, 2008Citations per year
Abstract: (arXiv)
The massive galaxies in the young universe, ten billion years ago, formed stars at surprising intensities. While this was commonly attributed to violent mergers, many of these galaxies seem to be extended rotating discs incompatible with mergers (Genzel et al. 2006, 2008). In order to uncover the origin of this phenomenon, we use a state-of-the-art cosmological simulation and clustering theory to explore how these galaxies acquired their gas. We find that these are 'Stream-Fed Galaxies', growing via steady, narrow, cold gas streams, which penetrate effectively through the shock-heated media of dark-matter haloes as massive as the Milky Way's. This confirms an earlier conjecture (Dekel & Birnboim 2006). Half the stream mass is in clumps leading to mergers of mass ratio 1:10 or higher, and half is in smoother flows. Since the merger duty cycle is 0.1, three-quarters of the galaxies forming stars at a given rate are fed by smooth streams. Unlike destructive major mergers, the smoother flows can keep the discs intact, though thick and perturbed. The observed abundance of star-forming galaxies implies that the inflowing gas turns into stars at maximum efficiency. In contrast, the sub-millimeter galaxies that form stars even more intensely are largely compact merger-induced starbursts in haloes twice as massive.References(36)
Figures(28)