The History of the Baryon Budget: Cosmic Logistics in a Hierarchical Universe

TL;DR

This paper uses high-resolution simulations and an analytical model to study the evolution of baryon distribution in galactic halos, highlighting the role of galactic winds and matching observational constraints.

Contribution

It introduces a simple analytical model for baryon evolution in halos, validated against simulations and observations, emphasizing wind effects and the anti-hierarchical star formation history.

Findings

Analytical model accurately predicts baryon phases in halos.

Galactic winds significantly influence baryon distribution.

Model parameters are tightly constrained by observations.

Abstract

Using a series of high-resolution N-body hydrodynamical numerical simulations, we investigate several scenarios for the evolution of the baryon budget in galactic halos. We derive individual halo star formation history (SFH), as well as the global star formation rate in the universe. We develop a simple analytical model that allows us to compute surprisingly accurate predictions, when compared to our simulations, but also to other simulations presented in Springel & Hernquist (2003). The model depends on two main parameters: the star formation time scale t* and the wind efficiency eta_w. We also compute, for halos of a given mass, the baryon fraction in each of the following phases: cold disc gas, hot halo gas and stars. Here again, our analytical model predictions are in good agreement with simulation results, if one correctly takes into account finite resolution effect. We compare predictions of our analytical model to several observational constraints, and conclude that a very narrow range of the model parameters is allowed. The important role played by galactic winds is outlined, as well as a possible `superwind' scenario in groups and clusters. The `anti-hierarchical' behavior of observed SFH is well reproduced by our best model with t*=3Gyr and eta_w=1.5. We obtain in this case a present-day cosmic baryon budget of Omega*= 0.004, Omega_cold=0.0004, Omega_hot=0.01 and Omega_back=0.02 (diffuse background).