On bursty star formation during cosmological reionization - how does it influence the baryon mass content of dark matter halos?

TL;DR

This study uses a semi-analytical model to explore how bursty star formation and feedback delays during reionization influence the baryon content of dark matter halos at high redshift, revealing mass-dependent gas retention and star formation efficiency effects.

Contribution

The paper introduces a semi-analytical model incorporating delayed feedback and reionization effects to analyze baryon content and star formation oscillations in early Universe halos.

Findings

Lower mass halos are gas deficient at high redshift.

Delayed feedback reduces star formation efficiency in higher mass halos.

Oscillations in gas mass are driven by feedback timing and star formation efficiency.

Abstract

The baryon mass content of dark matter halos in the early Universe depends on global factors - e.g. ionising ultraviolet (UV) radiation background - and local factors - e.g. star formation efficiency and assembly history. We use a lightweight semi-analytical model to investigate how local and global factors impact halo baryon mass content at redshifts of $z\geq 5$. Our model incorporates a time delay between when stars form and when they produce feedback, which drive bursts of star formation, and a mass and redshift dependent UV background, which captures the influence of cosmological reionization on gas accretion onto halos. We use statistically representative halo assembly histories and assume that the cosmological gas accretion rate is proportional to the halo mass accretion rate. Delayed feedback leads to oscillations in gas mass with cosmic time, behaviour that cannot be captured with instantaneous feedback. Highly efficient star formation drives stronger oscillations, while strong feedback impacts when oscillations occur; in contrast, inefficient star formation and weak feedback produce similar long-term behaviour to that observed in instantaneous feedback models. If the delayed feedback timescale is too long, a halo retains its gas reservoir but the feedback suppresses star formation. Our model predicts that lower mass systems ($\leq 10^7 \text{M}_\odot$) at $z \leq 10$ should be strongly gas deficient, whereas higher mass systems retain their gas reservoirs because they are sufficiently massive to continue accreting gas through cosmological reionization. Interestingly, in higher mass halos, the median $m_\star/(m_\star+m_\text{g}) \simeq 0.01-0.05$, but is a factor of 3-5 smaller when feedback is delayed. Our model does not include seed supermassive black hole feedback, which is necessary to explain massive quenched galaxies in the early Universe.