STRUCTURE OF MERGER REMNANTS .3. PHASE-SPACE CONSTRAINTS

This paper explores the evolution of the coarsely grained phase-space density in mergers and in galaxy formation. In particular, numerical s imulations are used to determine the properties of remnants produced b y ''major'' mergers between equal-mass galaxies. Contrary to some exis ting claims, remnants of mergers between stellar disks are found to la ck sufficient material at high phase-space densities to be identified as elliptica! galaxies. We quantify this effect by computing the cumul ative coarsely grained phase-space distribution, s(f)BAR, for the remn ants and compare it to that derived from simple models of the mass pro files of ellipticals. In so doing, we estimate that the discrepancy is confined to the inner approximately 15% of the stellar mass. In princ iple, this problem can be circumvented by dissipation in gas and star formation, but this process by itself probably requires that the proge nitors comprise a gas fraction approximately 25%-30% of their luminous mass. More directly, as shown by additional simulation, the phase-spa ce discrepancy can be reconciled by including compact bulges in the pr ogenitors having approximately 20%-25% the mass of the disks. We furth er speculate on the relevance of our analyses to more general situatio ns where the progenitor galaxies have very different masses or to remn ants produced from repeated mergers in a dense galactic environment. A number of observational signatures are noted which may help to establ ish the importance of merging to the structure and origin of early-typ e galaxies. In addition, we apply the methods developed here to the sa mple of hot stellar systems cataloged recently by Bender et al. A stro ng correlation is found between the luminosity of these objects and th e ''effective'' coarsely grained phase density (f(eff)BAR is-proportio nal-to 1/sigmar(eff)2). Implications of these findings for the interpr etation of the fundamental plane of elliptical galaxies are discussed.