High-Resolution Panchromatic Spectral Models of Galaxies including Photoionisation and Dust

An updated version of the dust radiation transfer code Sunrise, including models for star-forming regions and a self-consistent calculation of the spatially dependent dust and PAH emission, is presented. Given a hydrodynamic simulation of a galaxy, this model can calculate a realistic 2-dimensional ultraviolet–submillimeter spectral energy distribution of the galaxy, including emission lines from HII regions, from any viewpoint. To model the emission from star-forming regions, the MAPPINGSIII photoionization code is used. The high wavelength resolution (~ 1000 wavelengths) is made possible by the polychromatic Monte-Carlo algorithm employed by Sunrise. From the 2-D spectral energy distributions, images in any filter bands or integrated galaxy SEDs can be created. Using a suite of hydrodynamic simulations of disc galaxies, the output broad-band images and spectral energy distributions are compared with observed galaxies from the multiwavelength SINGS and SLUGS galaxy surveys. Overall, the output spectral energy distributions show a good match with observed galaxies in colours ranging from GALEX far-UV to SCUBA submillimeter wavelengths. The only possible exception is the 160 micron/850 micron colour, which the simulations underestimate by a factor “of order 5” compared to the SINGS sample. However, the simulations here agree with the SLUGS galaxies, which consistently have significantly larger amounts of cold dust than the SINGS galaxies. The Sunrise model can be used to generate simulated observations of arbitrary hydrodynamic galaxy simulations. In this way, predictions of galaxy formation theories can be directly tested against observations of galaxies.

💡 Research Summary

This paper presents an upgraded version of the radiative‑transfer code Sunrise that now incorporates self‑consistent treatment of star‑forming regions via the MAPPINGS III photo‑ionisation code and a spatially resolved calculation of dust and PAH emission. Given a hydrodynamic simulation of a galaxy, the combined Sunrise‑MAPPINGS III pipeline can generate a full two‑dimensional spectral energy distribution (SED) from the far‑ultraviolet to the sub‑millimeter with a wavelength resolution of roughly 1000 points, and it does so for any chosen line of sight. The key technical advances are: (1) embedding a physically motivated model of H II regions that supplies nebular emission lines (Balmer series,