Mathematics – Logic
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dda....37.0401c&link_type=abstract
American Astronomical Society, DDA meeting #37, #4.01; Bulletin of the American Astronomical Society, Vol. 38, p.668
Mathematics
Logic
Scientific paper
The Lambda cold dark matter cosmology, now strongly constrained by direct observation at early epochs, successfully describes the structure of the evolved universe on large and intermediate scales but suffers serious difficulties on smaller, galactic scales. Among the significant problems is a persistent discrepancy between observations of nearby galaxies, which imply that galactic dark matter haloes have flat cores, and the cosmological model, which predicts that the haloes should have a central density cusp. Using N-body simulations we show that random bulk gas motions in small primordial galaxies, of the magnitude expected in these systems, result in a flattening of the central dark matter cusp on short timescales (of order 100 million years). Gas bulk motions in early galaxies are driven by supernova explosions and stellar winds which result from ongoing star formation. During the subsequent evolution, most of the galactic gas will be consumed by star formation and lost via galactic winds, leaving a gas content in agreement with observations of present-day galaxies. Our mechanism is general and would have operated in all star-forming galaxies at redshifts > 10. Once removed, the cusp cannot be reintroduced during the subsequent merger hierarchy involved in building 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.
Support from NSERC, The Canadian Institute for Advanced Research and SHARCNET is gratefully acknowledged.
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