Formation and evolution of early-type galaxies

II. Models with quasi-cosmological initial conditions

Department of Astronomy, University of Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: [merlin;chiosi]@pd.astro.it

Received: 7 November 2005
Accepted: 12 April 2006

Abstract

Aims.In this study, with the aid of N-Body simulations based on quasi-cosmological initial conditions, we have followed the formation and evolution of two early-type galaxies of different total mass, from their separation from global expansion of the Universe to their collapse to virialized structures, the formation of stars and subsequent nearly passive evolution.

Methods.Using the pd-tsph N-Body code, we developed the simulations of two model galaxies in quasi-cosmological context. The cosmological background we have considered is the Standard CDM. The models are made of Dark and Baryonic Matter in standard cosmological proportions (9:1), and have significantly different initial total mass, i.e. (A) and (B). Particular care has been paid to the star formation process, heating and cooling of gas, and chemical enrichment.

Results.Star formation is completed within the first 3 Gyr in model A, whereas it lasts longer up to about 4 Gyr in model B. The models are followed for a long period of time, i.e. 13 Gyr (model A) and 5 Gyr (model B): in any case, well beyond the stages of active star formation. The structural properties of the present-day models are in good agreement with current observations. The chemical properties, mean metallicity and metallicity gradients also agree with available observational data. Finally, conspicuous galactic winds are found to occur.

Conclusions.The models conform to the so-called revised monolithic scheme, because mergers of substructures have occurred very early in the galaxy life. Our results agree with those obtained in other similar recent studies, thus strengthening the idea that the revised monolithic scheme is the right trail to follow in the forest of galaxy formation and evolution.