Bulge Formation: The Role of the Multi-Phase ISM

Summary

Star formation in bulges has likely been a rather efficient process. An efficient formation of stars depends strongly on the presence of metallic atoms and molecules. These species provide the necessary cooling for the ambient medium to sustain star formation. In order to assess the epoch and timescales for bulge-formation, it is therefore important to investigate the structure of the multi-phase ISM as a function of redshift and the formation of stars in such a medium. Calculations are presented which incorporate feedback effects and the thermal and chemical balance of interstellar gas. Predictions are made for the star formation histories of spheroids of various masses, and compared to similar estimates for disks.

Introduction

Star formation (SF) is a local phenomenon which must find its explanation in the stability and fragmentation of dense molecular clouds. Studies in our own Galaxy have focussed on the structure of dense proto-stellar cores and the chemical and thermal balance of star-forming regions. These studies lend indirect support to a Schmidt (1959) law, but emphasize the need to include explicitly the structure of the multi-phase ISM to model accurately the most important heating and cooling processes. A large unknown in these investigations is the role of feedback. Supernova explosions and stellar radiation associated with the process of SF influence the global physical structure of the interstellar gas which supports this process.