Involved people at OAB: Ciotti, D'Ercole, Londrillo.
In collaboration with G. Bertin (SNS-Pisa) Ciotti has clarified, using an analytical approach, some properties of the surface brightness profiles commonly used in observational works for the modeling of elliptical galaxies. The obtained simple relations (derived by using asymptotic expansion technique applied to the exact formulae of little use in practical applications) are of great utility both for the interpretation of real data and their modeling.
The Abel inversion has been generalized from spherical to toroidal symmetry. Such a generalization allows one to expand a generic density distribution, axially symmetric in a pseudo-basis of toroidal components. The obvious application of the developed technique is the reconstruction of the density distribution in S0 galaxies or astrophysical disks (planetary, galactic, and so on) from the observed (projected) density distribution.
On the subject of galaxy dynamics, the study of the dynamical constraints on the distribution and amount of dark matter in the central regions of elliptical galaxies and bulges has been extended and generalized. This investigation is carried out by using analytical methods developed by Ciotti in the past years. The results obtained can be used in many applications, e.g., in the assignment of the initial conditions for multi-component N-body simulations or in the construction of realistic (self-consistent) models to be used in the modeling of observations. For example, in collaboration with Londrillo (who for this purpose developed a parallel particle-mesh numerical code) they are investigating the stability of elliptical galaxies in the presence of dark matter halos.
Another collaboration of Ciotti with G. Bertin and Londrillo concerns the construction of a family of phase-space distribution functions, obtained by a tailored flattening of truncated, anisotropic polytropes. The explicit form of these functions is very simple. The associated density profiles (obtained by solving numerically, with a numerical code developed by Londrillo, the associated non-linear Poisson equation) are of considerable interest, reproducing in a physically sound framework the main properties of complex dynamical systems like the so-called ``peanut-shaped'' bulges.
Ciotti, D'Ercole and S. Recchi (University of Trieste), completed a study about the effects of tidal interactions on the hot X-ray ISM of elliptical galaxies. This study has been done adopting a 2D hydro code developed by D'Ercole. In particular, it revealed the formation of cold filaments of a few kpc embedded in the X-ray halo. In some ellipticals such filaments are indeed observed.
In collaboration with J.P. Ostriker (Princeton University) Ciotti has developed an evolutive scenario which links the X-ray evolution of elliptical galaxies with QSO evolution and activity. They propose a solution of a puzzling question: according to them the lack of strong AGN activity in the large majority of elliptical galaxies containing a massive black hole at their center (activity naturally predicted in the standard cooling flow scenario) is due to an accretion mechanism modulated by radiation feedback. The feedback is due to Compton scattering of the radiation emitted by the accreting material on the electrons of the galactic hot gaseous halo. This scenario has been explored in great detail by using a specific numerical hydrocode which takes into account several aspects of radiative transfer.
Other research projects were started by our group in 1999 and should be completed in 2000: a detailed investigation of the physical origin of the fundamental plane of elliptical galaxies, the study of the dynamics of dark matter halos in elliptical galaxies, the numerical simulation of X-ray halos of elliptical galaxies, the study of resonance phenomena between stellar orbits in galaxies and the cluster tidal field, the interaction of the globular cluster system and the density profile of the parent galaxy, the extension of the applicability range of the feedback modulated accretion solutions on black holes.
In 1999 D'Ercole studied the ISM of elliptical galaxies. He also studied the ISM evolution in starburst galaxies. In collaboration with Brighenti (University of Bologna) they performed 2D simulations, taking into account galactic rotation and thermal conduction, in order to describe the circulation of metals ejected by SNsII in such systems. The models show that metals are partially lost by the galactic wind powered by SNsII, while the condition for a second star formation burst are created again after 1 Gyr from the previous burst.
In collaboration with F. Matteucci e S. Recchi (University of Trieste), D'Ercole also made numerical hydrodynamical models which take into account the chemical evolution in starburst galaxies. through the implementation of a code used for one-zone chemical models. In these models the activity of SNsI and SNsII is considered.
In collaboration with S. Pellegrini (University of Bologna) D'Ercole and Ciotti, they are performing a number of numerical 2D simulations to study the effect of the merging with a dwarf galaxy on the X-ray emission of the target elliptical galaxy.