Triggered Population III star formation: the effect of H$_2$ self-shielding

TL;DR

This study compares methods for modeling H$_2$ self-shielding in Population III star formation, finding that the density gradient approximation offers a good balance of accuracy and computational efficiency for galaxy simulations.

Contribution

It evaluates and compares local approximations to direct integration for H$_2$ self-shielding, recommending the density gradient method for larger-scale simulations.

Findings

Direct integration and density gradient approaches prevent secondary star formation.

The approximate method is twice as fast as direct integration.

Jeans length overestimates H$_2$ column density by a factor of 10.

Abstract

The multiplicity of metal-free (Population III) stars may influence their feedback efficiency within their host dark matter halos, affecting subsequent metal enrichment and the transition to galaxy formation. Radiative feedback from massive stars can trigger nearby star formation in dense self-shielded clouds. In model radiation self-shielding, the H$_2$ column density must be accurately computed. In this study, we compare two local approximations based on the density gradient and Jeans length with a direct integration of column density along rays. After the primary massive star forms, we find that no secondary stars form for both the direct integration and density gradient approaches. The approximate method reduces the computation time by a factor of 2. The Jeans length approximation overestimates the H$_2$ column density by a factor of 10, leading to five numerically enhanced self-shielded, star-forming clumps. We conclude that the density gradient approximation is sufficiently accurate for larger volume galaxy simulations, although one must still caution that the approximation cannot fully reproduce the result of direct integration.