Diversity of dwarf galaxy IR-submm emission patterns: CLUES from hydrodynamical simulations

Abstract

The spectral energy distributions (SEDs) of low-mass low-metallicity (dwarf) galaxies are a challenging piece of the puzzle of galaxy formation in the near Universe. These SEDs show some particular features in the submillimeter to far-infrared wavelength range compared to normal, larger, and metal-richer galaxies that cannot be explained by the current models. These can be summarized as: a broadening of the IR peak, which implies a warmer dust component; an excess of emission in the submm ($\sim$500 $\mu$m), that causes a flattening of the submm/FIR slope; and a very low intensity of PAH emission features. With the aim of explaining these emission patterns, the SEDs of a sample of 27 simulated dwarf galaxies were calculated using the GRASIL-3D radiation transfer code. This code has the particularity that it separately treats the radiative transfer through dust grains within molecular clouds and within the cirrus, the dense and diffuse components of the gas phase, respectively. The simulated galaxies have stellar masses ranging from 10$^6$-10$^9$ M$_\odot$, and were obtained from a single simulation run within a Local Group environment with initial conditions from the CLUES project. We report a study of the IRAS, Spitzer and Herschel bands luminosities, and of the SFRs, dust, and gas (HI and H$_2$) mass contents. We find a satisfactory agreement with observational data, with GRASIL-3D naturally reproducing the specific spectral features mentioned above. We conclude that the GRASIL-3D two-component dust model gives a physical interpretation of the emission of dwarf galaxies: molecular clouds and cirrus represent the warm and cold dust components, respectively, needed to reproduce observational data.