Two-Phase Galaxy Formation

Understand

We propose and test a scenario for the assembly and evolution of luminous matter in galaxies which substantially differs from that adopted by other semianalytic models.

• As for the dark matter (DM), we follow the detailed evolution of halos within the canonical LCDM cosmology using standard Montecarlo methods.
• However, when overlaying prescriptions for baryon evolution, we take into account an effect pointed out in the past few years by a number of studies mostly based on intensive N-body simulations, namely that typical halo growth occurs in two phases: an early, fast collapse phase featuring several major merger events, followed by a late, quiescent accretion onto the halo outskirts.
• We propose that the two modes of halo growth drive two distinct modes for the evolution of baryonic matter, favoring the development of the spheroidal and disc components of galaxies, respectively.