Should Elliptical Galaxies Be Idealised as Collisionless Equilibria?

A review of the present observational and theoretical status of elliptical galaxies is presented with the aim to clarify whether the monolithic or the hierarchical, is a more viable scenario for the origin of these structures. We describe the dynamical structure of elliptical galaxies using photometric and spectroscopic data, in particular 3D observations from integral field spectrographs, with emphasis on properties such as brightness distribution, velocity profiles, central...

We investigate detailed kinematical properties of simulated collisionless merger remnants of disk galaxies with mass ratios of 1:1 and 3:1. The simulations were performed by direct summation using the new special hardware device GRAPE-5. In agreement with observations, the shape of the line-of-sight velocity distribution (LOSVD) is Gaussian with small deviations. For most cases we find that the retrograde wings of the LOSVD are steeper than the prograde ones. This is in contr...

I will present recent theoretical results on the formation and the high redshift assembly of spheroids. These findings have been obtained by utilising different and complementary techniques: chemodynamical models offer great insight in the radial abundance gradients in the stars; while state semi-analytic codes implementing a detailed treatment of the chemical evolution allow an exploration of the role of the galactic mass in shaping many observed relations. The results will ...

The kinematics of the outer parts of three intermediate-luminosity elliptical galaxies have been studied using the Planetary Nebula Spectrograph. The galaxies' velocity dispersion profiles are found to decline with radius; dynamical modeling of the data indicates the presence of little if any dark matter in these galaxies' halos. This surprising result conflicts with findings in other galaxy types, and poses a challenge to current galaxy formation theories.

We present results of a study on the evolution of the parameters characterizing the structure and dynamics of the relaxed elliptical-like objects (ELOs) identified at z=0, z=1 and z=1.5 in a set of hydrodynamical, self-consistent simulations operating in the context of a concordance cosmological model. The values of the stellar mass, the stellar half-mass radius and the stellar mean-square velocity have been measured in each ELO and found to populate, at any z, a flattened el...

It is shown that the cuspy density distributions observed in the cores of elliptical galaxies can be realized by dissipationless gravitational collapse. The initial models consist of power-law density spheres such as $\rho\propto r^{-1}$ with anisotropic velocity dispersions. Collapse simulations are carried out by integrating the collisionless Boltzmann equation directly, on the assumption of spherical symmetry. From the results obtained, the extent of constant density cores...

Under the merger hypothesis, elliptical galaxies are built through mergers of gas-rich spirals. However, the relative paucity of HI in most normal ellipticals demands significant processing of atomic gas into other forms if this process is to be viable. Here I present a few qualitative remarks on how the properties of merger-spawned ellipticals might depend on the (evolving) gas content of the progenitor disks, then turn to a more quantitative study of the constraints provide...

A fundamental gap in the current understanding of galaxies concerns the thermodynamical evolution of the ordinary, baryonic matter. On one hand, radiative emission drastically decreases the thermal energy content of the interstellar plasma (ISM), inducing a slow cooling flow toward the centre. On the other hand, the active galactic nucleus (AGN) struggles to prevent the runaway cooling catastrophe, injecting huge amount of energy in the ISM. The present study intends to deepl...

Theories of how galaxies, the fundamental constituents of large-scale structure, form and evolve have undergone a dramatic paradigm shift in the last few decades. Earlier views were of rapid, early collapse and formation of basic structures, followed by slow evolution of the stellar populations and steady buildup of the chemical elements. Current theories emphasize hierarchical buildup via recurrent collisions and mergers, separated by long periods of relaxation and secular r...

The discovery of a population of massive, compact and quiescent early-type galaxies has changed the view on plausible formation scenarios for the present day population of elliptical galaxies. Traditionally assumed formation histories dominated by 'single events' like early collapse or major mergers appear to be incomplete and have to be embedded in the context of hierarchical cosmological models with continuous gas accretion and the merging of small stellar systems (minor me...