CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations III. The physics behind the emergence of the golden mass scale

TL;DR

This study uses cosmological simulations to explore the origin and evolution of the 'golden mass' scale in galaxies, revealing how feedback processes and cosmology influence star formation efficiency and galaxy quenching over cosmic time.

Contribution

It provides a detailed analysis of how feedback mechanisms and cosmological parameters shape the emergence and evolution of the golden mass scale in galaxy formation.

Findings

The dark-to-stellar mass ratio exhibits a U-shaped relation with stellar mass, with a minimum at the golden mass.

Feedback processes, especially SN and AGN feedback, significantly influence the position and properties of the golden mass.

The timing and characteristics of the golden mass are affected by feedback strength and evolve with redshift.

Abstract

We investigate the origin and evolution of the "golden mass" (halo mass $\sim10^{12} \, \rm M_{\odot}$, stellar mass $\sim5 \times 10^{10} \, \rm M_{\odot}$), linked to peak star formation efficiency, using \textsc{camels} simulations based on IllustrisTNG. Exploring a range of SN/AGN feedback strengths and cosmologies ($\Omega_{\rm m}, \sigma_8$), we find a U-shaped relation between dark-to-stellar mass ratio and stellar mass, with a minimum at the golden mass, in line with observations. Cosmology affects the normalization of this relation, while feedback shapes its form and the emergence of the golden mass. Stronger SN feedback lowers its value; AGN feedback, especially radiative efficiency, alters the high-mass slope and shifts the golden mass. The golden mass appears earlier with stronger feedback, which quenches star formation more rapidly. Passive galaxies retain the U-shape; star-forming ones show decreasing dark matter fraction with stellar mass, with possible reversal at low redshift. Global stellar fractions also exhibit a U-shaped trend: in passive galaxies, the golden mass shifts to lower masses or vanishes; in star-forming ones, it emerges only at low redshift. Feedback governs the golden mass up to $z \sim 1.5-2$, with a secondary role from cold streams and virial shocks. We speculate that at $z \gtrsim 1.5-2$, a single stream-regulated scale governs galaxy growth, which later bifurcates into two: a low-mass scale tied to gas richness and a higher-mass golden mass regulating efficiency and quenching. (abridged)