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M. Bernardi (Carnegie Mellon University), SDSS Collaboration
Galaxy formation remains one of the unsolved mysteries in cosmology. It is a complex process, involving both gravity and hydrodynamics, and can be complicated by such ingredients as turbulence, magnetic fields, black-hole formation and accretion, nuclear activity, tidal and merger interactions. Although the physics of disk formation has made considerable progress, we do not have an adequate understanding of spheroid formation. The homogeneity of the early-type population suggests that these galaxies may have formed from a single monolithic collapse. This is in contradiction with recently favored models of hierarchical galaxy formation which postulate that early-type galaxies are assembled at late times by stochastic mergers of less-massive galaxies. Environmental effects together with correlations between observables, as for e.g. the color-velocity dispersion relation, can be used to discriminate between models in which galaxies form at high redshift from a single monolithic collapse, or from a sequence of stochastic mergers at lower redshift. Using early-type galaxy observables extracted from the SDSS database I will show that: 1) galaxies in higher density regions tend to be more massive but not older than their counterparts in low density regions, and 2) independently of the environment, the more massive galaxies are also the older ones. These results combined with other findings from the SDSS allow for a sharp test of galaxy formation theory.
The author(s) of this abstract have provided an email address for comments about the abstract: bernardi@cmu.edu
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.