The role of young and evolved stars in the heating of dust in local galaxies

¹ INAF – Istituto di Radioastronomia, Via Gobetti 101, I-40129 Bologna, Italy
² Dipartimento di Fisica e Astronomia, Alma Mater Studiorum Università di Bologna, Via Piero Gobetti 93/2, I-40129 Bologna, Italy
³ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁵ Dept. Física Teórica y del Cosmos, Universidad de Granada, Granada, Spain
⁶ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, 18071 Granada, Spain
⁷ Instituto de Radioastronomía y Astrofísica (IRyA), Universidad Nacional Autónoma de México (UNAM), Antigua Carretera a Pátzcuaro, 8701, Ex-Hda. San José de la Huerta, Morelia, Michoacán 58089, Mexico
⁸ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
⁹ Departamento de Física de la Tierra y Astrofísica, Fac. de C.C. Físicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain
¹⁰ Instituto de Física de Partículas y del Cosmos, IPARCOS, Fac. C.C. Físicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain

^⋆ Corresponding author: vidhiritesh.tailor@unibo.it

Received: 9 April 2025
Accepted: 14 July 2025

Abstract

Context. Dust is a fundamental component of the interstellar medium (ISM) and plays a critical role in shaping galaxy evolution. Dust grains influence the ISM by cooling the gas, altering its chemistry, absorbing stellar radiation, and re-emitting it at longer wavelengths in the FIR and submillimetre (sub-mm) regimes. The cold dust component, which constitutes the majority of the dust mass, is primarily heated by stellar radiation, with contributions from both young, massive stars and the diffuse emission from older stellar populations. It is essential to discern how dust is heated to better understand the relationship between stellar populations and their surrounding environments.

Aims. This study aims to identify the dominant heating mechanisms responsible for the cold dust component in typical nearby spiral galaxies and to explore the contributions of both young and evolved stellar populations to dust heating.

Methods. Using a sample of 18 large, face-on spiral galaxies from the DustPedia project, we employed two complementary approaches. In the first method, we studied the correlations between the dust temperature (T_dust), star-formation rate (SFR) surface density (Σ_SFR), and stellar mass surface density (Σ_M*). In the second method, we explored the relationship between T_dust and the dust mass surface density (Σ_dust).

Results. By analyzing the median temperature radial profile, we find that T_dust peaks at ∼24 K at the galaxy centre, decreasing to ∼15 K toward the galaxy outskirts. Our analysis shows similar T_dust in galaxies with and without a central active galactic nucleus (AGN), suggesting that AGN activity does not significantly influence T_dust values and distribution on the spatial scales covered by our data, which range from 0.3 to 3 kpc. For ∼72% of the galaxies in our sample, the methods consistently identify the primary dust heating source. However, when considering the entire galaxy sample, our analysis suggests that there is no single dominant heating mechanism. We find that both young and evolved stars contribute to dust heating, with their relative contributions varying across galaxies.