Cosmic dust! Seemingly insignificant in the grand scheme of things, yet so pivotal for the evolution of galaxies. Although it is only but a small fraction of the interstellar medium, dust is ubiquitous, and is responsible for absorbing approximately one third of the energy emitted by stars in late-type galaxies in the local Universe.
Dust heating is mainly attributable to the absorption of ultraviolet and optical photons emitted by the youngest (~100 million years) stars. Dust reprocesses the absorbed energy and releases it as mid- and far-infrared radiation. This thermal re-emission by dust is often linked to the star-formation activity of a galaxy. However, several studies argue that the contribution to dust heating by much older stellar populations might be more significant. Advances in radiation transfer simulations finally allow us to actually quantify the heating mechanisms of diffuse dust by the stellar radiation field.
In this study, we constructed detailed 3D stellar and dust radiative transfer models in order to analyze the contribution of the different stellar populations to the dust heating in four nearby face-on barred galaxies: NGC1365, M83, M95, and M100. In this way, we were able to quantify the fraction directly related to young stellar populations, both globally and on local scales.
Left: Face-on view of the heating fraction of dust by the young stellar population in M83, as obtained from the 3D radiative transfer modelling. The bulge region is indicated with a red circle and the bar region with a blue ellipse.
Right: Distribution of the dust cell heating fractions, weighted by dust mass. The black line is the median value.
We show that the young stellar populations are the main contributors to the dust heating, donating, on average ~59% of their luminosity to this purpose throughout the galaxy. This dust-heating fraction drops to ~53% in the bar region and ~38% in the bulge region where the old stars are the dominant contributors to the dust heating.
If you are interested in this work and want to learn more, then please follow this link by clicking here.
---------------------------------------------------------------------------------------------------------------------------
Here, I present the radiative transfer model of NGC1365 at three different viewing angles. Each frame represents a different wavelength, ranging from the UV to the submm regime (in total 250 wavelengths).
Earth-view
Face-on view
Edge-on view