EMERGE - An empirical model for the formation of galaxies since
B. Moster, T. Naab, and S. White. (2017)cite arxiv:1705.05373Comment: 31 pages, 19 figures, 10 tables, submitted to MNRAS.
We present EMERGE, an Empirical ModEl for the foRmation of GalaxiEs,
describing the evolution of individual galaxies in large volumes from $z\sim10$
to the present day. We assign a star formation rate to each dark matter halo
based on its growth rate, which specifies how much baryonic material becomes
available, and the instantaneous baryon conversion efficiency, which determines
how efficiently this material is converted to stars, thereby capturing the
baryonic physics. Satellites are quenched following the delayed-then-rapid
model, and they are tidally disrupted once their subhalo has lost a significant
fraction of its mass. The model is constrained with observed data extending out
to high redshift. The empirical relations are very flexible, and the model
complexity is increased only if required by the data, assessed by several model
selection statistics. We find that for the same final halo mass galaxies can
have very different star formation histories. Nevertheless, the average star
formation and accretion rates are in good agreement with models following an
abundance matching strategy. Galaxies that are quenched at $z=0$ typically have
a higher peak star formation rate compared to their star-forming counterparts.
The accretion of stars can dominate the total mass of massive galaxies, but is
insignificant for low-mass systems, independent of star-formation activity.
EMERGE predicts stellar-to-halo mass ratios for individual galaxies and
introduces scatter self-consistently. We find that at fixed halo mass, passive
galaxies have a higher stellar mass on average. The intra-cluster-mass in
massive haloes can be up to 8 times larger than the mass of the central galaxy.
Clustering for star-forming and quenched galaxies is in good agreement with
observational constraints, indicating a realistic assignment of galaxies to