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Dry Mergers and the Formation of Early-Type Galaxies: Constraints from Lensing and Dynamics
Ist Teil von
The Astrophysical journal, 2009-10, Vol.703 (2), p.1531-1544
Ort / Verlag
Bristol: IOP Publishing
Erscheinungsjahr
2009
Link zum Volltext
Quelle
Electronic Journals Library
Beschreibungen/Notizen
Dissipationless (gas-free or 'dry') mergers have been suggested to play a major role in the formation and evolution of early-type galaxies, particularly in growing their mass and size without altering their stellar populations. We perform a new test of the dry-merger hypothesis by comparing N-body simulations of realistic systems to empirical constraints provided by recent studies of lens early-type galaxies. We find that major and minor dry mergers (1) preserve the nearly isothermal structure ( Delta *rtot r -2) of early-type galaxies within the observed scatter, (2) do not change more than the observed scatter the ratio between total mass M and 'virial' mass R e Delta *s2 e2/2G (where R e is the half-light radius and Delta *se2 is the projected velocity dispersion), (3) strongly increase galaxy sizes (R e M 0.85+/-0.17) and weakly increase velocity dispersions ( Delta *se2 M 0.06+/-0.08) with mass, thus moving galaxies away from the local observed M-R e and M- Delta *se2 relations, and (4) introduce substantial scatter in the M-R e and M- Delta *se2 relations. Our findings imply that-unless there is a high degree of fine tuning of the mix of progenitors and types of interactions-present-day massive early-type galaxies could not have assembled more than ~50% of their mass, and increased their size by more than a factor ~1.8, via dry merging.