The Fundamental Scaling Relations of Elliptical Galaxies

Abstract

We examine the fundamental scaling relations of elliptical galaxies formed through mergers. Using hundreds of simulations to judge the impact of progenitor galaxy properties on the properties of merger remnants, we find that gas dissipation provides an important contribution to tilt in the fundamental plane (FP) relation. Dissipationless mergers of disks produce remnants that occupy a plane similar to that delineated by the virial relation. As the gas content of progenitor disk galaxies is increased, the tilt of the resulting FP relation increases and the slope of the Re-M star relation steepens. For gas fractions f(gas) > 30%, the simulated FP scalings (R-e alpha sigma I-1.55(e)-0.82) approach those observed in the K band(R-e alpha sigma:(1.53) I-e(-0.79)). The dissipationless merging of spheroidal galaxies and the remerging of disk galaxy remnants roughly maintain the tilt of the FP occupied by the progenitor ellipticals., Dry merging of spheroidal systems at redshifts z < 1 is then expected to maintain the stellar-mass FP relations imprinted by gas-rich merging during the epoch of rapid spheroid and supermassive black hole growth at redshifts z approximate to 1-3. We estimate that approximate to 40%-100% of the FP tilt induced by structural properties, as opposed to stellar population effects, owes to trends in the central total-to-stellar mass ratio M-total/ M star produced by dissipation. Gas cooling allows for an increase in central stellar phase-space density relative to dissipationless mergers, thereby decreasing the central M-total/M star. Lower mass systems obtain greater phase-space densities than higher mass systems, producing a galaxy mass-dependent central M-total/M star and a corresponding tilt in the FP. We account for these trends in the importance of dissipation with galaxy mass in terms of the inefficient cooling of collisionally heated gas in massive halos and dynamically varying gas consumption timescales in smaller systems.