Accurate Photoionization Models of Nebula in Three Dimensions

Abstract

Accurate predictions of the physics of interstellar medium are vital for understanding galaxy formation and evolution. Modeling photoionized regions with complex geometry produces realistic ionization structures within the nebulae, providing the necessary physical predictions to interpret data. 3D photoionization codes built with Monte Carlo techniques provide powerful tools to produce the ionizing radiation field with fractal geometry, which includes the regions ionized by both stellar and diffuse photons.

In the first part of this thesis, we will present the observation of four nearby HII regions in the Large Magellanic Cloud and the Small Magellanic Cloud through the integral field spectrograph. Our observations demonstrate that the current photoionization models cannot reproduce the complex structures of the nebulae. A new self-consistent photoionization model with arbitrary geometry is required.

In the second part of this thesis, we will present a new self-consistent three-dimensional photoionization code -- Messenger Monte-Carlo MAPPINGS V (M3), which is designed for modeling nebulae in arbitrary three-dimensional geometries. The new code passes the Kentucky benchmark test to guarantee its accuracy of producing emission-line fluxes. We also create the diffuse ionized gas by using the new photoionization code.

The third part of this thesis presents one example nebula model with fractal geometries in 3D, created by the new Monte Carlo MAPPINGS code. The fluxes of emission-lines preferentially located at the nebular boundary are larger in the fractal model than the equivalent spherical model. This thesis is the first to demonstrate the dependence of emission-line behaviors on nebular geometry from theoretical photoionization models.

We present the future work in the final part of this thesis. We propose to combine radiation hydrodynamic simulations with the Monte Carlo photoionization code to produce the nebula shaped by stellar feedback. Our research has important implications for studies of the fundamental properties of galaxies using emission lines in the era of large IFU surveys and JWST. Show more