Giant disk galaxies, dwarfs and Lyman alpha clouds

摘要

If one omits early-type galaxies and high-density regions, disk galaxies form a one-dimensional sequence, characterized by galaxy mass (or rotation velocity). This sequence has a top and a bottom end. Three stages are involved in the formation of a galaxy and the complexities explain why the sequence has these two distinct ends. The numerous, low-column-density Lyman alpha 'forest' absorption lines at low redshift seem to be mainly associated with galaxy groups, rather than with individual galaxies. 'Failed dwarf galaxies' near the bottom end of the mass sequence (where thermal equilibrium matches the Virial temperature) are attractive candidates for providing the absorption. (C) 1999 Elsevier Science B.V. All rights reserved. [References: 44]