Publication: The removal of cusps from galaxy centres by stellar feedback in the early Universe

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Title	The removal of cusps from galaxy centres by stellar feedback in the early Universe
Authors/Editors*	S. Mashchenko, J. Wadsley, H. Couchman
Where published*	Nature
How published*	Journal
Year*	2006
Volume	442
Number
Pages	539-541
Publisher
Keywords
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Abstract	The standard cosmological model, now strongly constrained by direct observations of the Universe at early epochs, is very intermediate scales. Unfortunately, serious contradictions remain on smaller, galactic scales. Among the main small-scale problems is a significant and persistent discrepancy between observations of nearby galaxies, which imply that galactic dark matter haloes have a density profile with a flat core, and the cosmological model, which predicts that the haloes should have divergent density (a cusp) at the centre. Here we report numeri- cal simulations that show that random bulk motions of gas in small primordial galaxies, of the magnitude expected in these on relatively short timescales (~10^8 years). Gas bulk motions in early galaxies are driven by supernova explosions that result from ongoing star formation. Our mechanism is general, and would have operated in all star-forming galaxies at redshifts z>=10. Once removed, the cusp cannot be reintroduced during the subsequent mergers involved in the build-up of larger galaxies. As a consequence, in the present Universe both small and large galaxies would have flat dark matter core density profiles, in agreement with observations.