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

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. 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. 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_ ̊m dust )), star-formation rate (SFR) surface density ((Σ_ ̊m SFR )), and stellar mass surface density ((Σ_ M_* )). In the second method, we explored the relationship between (T_ ̊m dust ) and the dust mass surface density ((Σ_ ̊m dust ̊m dust ) peaks at ∼24 K at the galaxy centre, decreasing to ∼15 K toward the galaxy outskirts. Our analysis shows similar (T_ ̊m dust ) in galaxies with and without a central active galactic nucleus (AGN), suggesting that AGN activity does not significantly influence (T_ ̊m 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.