A Global Semi-Analytic Model of the First Stars and Galaxies Including Dark Matter Halo Merger Histories

TL;DR

This paper introduces a comprehensive semi-analytic model for the formation of the first stars and galaxies at high redshift, incorporating detailed dark matter merger histories and feedback effects, to better understand early cosmic star formation.

Contribution

It presents a new self-consistent semi-analytic model calibrated with recent simulations, including halo merger histories and feedback, improving predictions of early star formation rates.

Findings

PopIII star formation rate density is over an order of magnitude higher at z=35-15 compared to previous models.

Halo-to-halo scatter increases PopIII stellar mass density by about 1.5 times at z>15.

Models assuming smooth halo growth may underestimate PopIII SFRD under strong feedback conditions.

Abstract

We present a new self-consistent semi-analytic model of the first stars and galaxies to explore the high-redshift ($z{>}15$) Population III (PopIII) and metal-enriched star formation histories. Our model includes the detailed merger history of dark matter halos generated with Monte Carlo merger trees. We calibrate the minimum halo mass for PopIII star formation from recent hydrodynamical cosmological simulations that simultaneously include the baryon-dark matter streaming velocity, Lyman-Werner (LW) feedback, and molecular hydrogen self-shielding. We find an overall increase in the resulting star formation rate density (SFRD) compared to calibrations based on previous simulations (e.g., the PopIII SFRD is over an order of magnitude higher at $z=35-15$). We evaluate the effect of the halo-to-halo scatter in this critical mass and find that it increases the PopIII stellar mass density by a factor of ${\sim}1.5$ at $z{>}15$. Additionally, we assess the impact of various semi-analytic/analytic prescriptions for halo assembly and star formation previously adopted in the literature. For example, we find that models assuming smooth halo growth computed via abundance matching predict SFRDs similar to the merger tree model for our fiducial model parameters, but that they may underestimate the PopIII SFRD in cases of strong LW feedback. Finally, we simulate sub-volumes of the Universe with our model both to quantify the reduction in total star formation in numerical simulations due to a lack of density fluctuations on spatial scales larger than the simulation box, and to determine spatial fluctuations in SFRD due to the diversity in halo abundances and merger histories.