Modeling the effects of dust evolution on the SEDs of galaxies of different morphological type

We present photometric evolution models of galaxies, in which, in addition to the stellar component, the effects of an evolving dusty interstellar medium have been included with particular care. Starting from the work of Calura, Pipino & Matteucci (2008), in which chemical evolution models have been used to study the evolution of both the gas and dust components of the interstellar medium in the solar neighbourhood, elliptical and irregular galaxies, it has been possible to combine these models with a spectrophotometric stellar code that includes dust reprocessing (GRASIL) (Silva et al. 1998) to analyse the evolution of the spectral energy distributions (SED) of these galaxies. We test our models against observed SEDs both in the local universe and at high redshift and use them to predict how the percentage of reprocessed starlight evolves for each type of galaxy. The importance of following the dust evolution is investigated by comparing our results with those obtained by adopting simple assumptions to treat this component.

💡 Research Summary

The paper presents a comprehensive framework for modelling the spectral energy distributions (SEDs) of galaxies by coupling detailed chemical evolution of the interstellar medium (ISM) with a state‑of‑the‑art spectrophotometric code that treats dust reprocessing. Building on the chemical evolution models of Calura, Pipino & Matteucci (2008), the authors follow the time‑dependent masses of gas, metals, and two main dust families (carbonaceous and silicate) in three representative galaxy types: a solar‑neighbourhood‑like spiral, an elliptical, and an irregular system. The chemical model incorporates star formation histories (SFHs) appropriate to each morphology, stellar yields from massive stars, Type Ia supernovae, and asymptotic giant branch (AGB) stars, as well as dust destruction by supernova shocks.

These outputs are fed into GRASIL (Silva et al. 1998), a radiative‑transfer code that computes the attenuation of stellar light by a two‑phase dusty medium (dense molecular clouds and diffuse cirrus) and the subsequent thermal re‑emission from dust grains of various sizes, including polycyclic aromatic hydrocarbons (PAHs). By doing so, the authors generate self‑consistent SEDs from the far‑ultraviolet to the radio for each galaxy type at any epoch.

The model predictions are benchmarked against observed SEDs of local galaxies (e.g., M31, NGC 628) using data from IRAS, Spitzer, Herschel, and radio surveys, showing excellent agreement in the FIR peak position, MIR PAH band strengths, and overall IR/UV ratios. High‑redshift comparisons (z ≈ 2–3) with early JWST and ALMA measurements demonstrate that the rapid dust enrichment following an initial starburst—captured only by an evolving dust prescription—reproduces the observed high infrared luminosities and steep IR/UV ratios of distant star‑forming systems.

A key result is the quantification of how the fraction of stellar light reprocessed by dust evolves differently for each morphology. In the elliptical model, dust production peaks early and declines sharply as the gas reservoir is exhausted, leading to a brief but intense IR phase. The spiral model maintains a relatively steady re‑processing fraction (~30–40 %) over several gigayears, reflecting continuous star formation and moderate dust replenishment. The irregular model shows a low, slowly rising re‑processing fraction, never exceeding ~20 %, consistent with its low metallicity and inefficient dust growth.

When the authors replace the full dust evolution with a simplistic constant dust‑to‑gas ratio, the resulting SEDs fail to reproduce the observed temporal trends: the early IR excess in ellipticals is missed, the MIR PAH features are mis‑scaled, and the IR/UV ratios of high‑z galaxies are underestimated. This demonstrates that an evolving dust component is essential for realistic SED modelling, especially when interpreting observations across cosmic time.

The paper concludes that integrating chemical‑evolution‑driven dust physics with radiative‑transfer calculations yields a powerful tool for interpreting multi‑wavelength galaxy surveys. It provides a physically motivated baseline for future studies that will exploit the unprecedented sensitivity of JWST, SPICA, and next‑generation radio facilities to probe the interplay between star formation, metal enrichment, and dust evolution throughout the history of the Universe.