Smoothed Particle Hydrodynamics simulations of expanding HII regions. I. Numerical methods and tests

TL;DR

This paper introduces a new adaptive algorithm for simulating the effects of ionizing radiation in star formation using SPH, enabling detailed and efficient modeling of HII region expansion and interactions.

Contribution

The paper presents a novel, adaptive HEALPix-based algorithm for including ionizing radiation effects in SPH simulations, improving efficiency and resolution in modeling star formation processes.

Findings

Successfully simulated spherical and off-center HII region expansions

Demonstrated the algorithm's ability to model cloud dispersal and core ablation

Enabled exploration of ionizing radiation's role in star formation regulation

Abstract

We describe a new algorithm for including the dynamical effects of ionizing radiation in SPH simulations, and we present several examples of how the algorithm can be applied to problems in star formation. We use the HEALPix software to tessellate the sky and to solve the equation of ionization equilibrium along a ray towards each of the resulting tesserae. We exploit the hierarchical nature of HEALPix to make the algorithm adaptive, so that fine angular resolution is invoked only where it is needed, and the computational cost is kept low. We present simulations of (i) the spherically symmetric expansion of an HII region inside a uniform-density, non--self-gravitating cloud; (ii) the spherically symmetric expansion of an HII region inside a uniform-density, self-gravitating cloud; (iii) the expansion of an off-centre HII region inside a uniform-density, non--self-gravitating cloud, resulting in rocket acceleration and dispersal of the cloud; and (iv) radiatively driven compression and ablation of a core overrun by an HII region. The new algorithm provides the means to explore and evaluate the role of ionizing radiation in regulating the efficiency and statistics of star formation.