The bolometric and UV attenuation in normal spiral galaxies of the Herschel Reference Survey

TL;DR

This study models the UV-to-submillimetre spectral energy distributions of nearby spiral galaxies to quantify dust absorption and re-emission, revealing correlations with galaxy type and star formation activity.

Contribution

It introduces a self-consistent framework to estimate dust attenuation and UV heating fractions in spiral galaxies, improving understanding of dust effects on galaxy spectra.

Findings

Average 32% of starlight absorbed by dust

56% of dust luminosity from UV photons

Higher UV heating fractions in later-type spirals

Abstract

The dust in nearby galaxies absorbs a fraction of the UV-optical-near-infrared radiation produced by stars. This energy is consequently re-emitted in the infrared. We investigate the portion of the stellar radiation absorbed by spiral galaxies from the HRS by modelling their UV-to-submillimetre spectral energy distributions. Our models provide an attenuated and intrinsic SED from which we find that on average 32 % of all starlight is absorbed by dust. We define the UV heating fraction as the percentage of dust luminosity that comes from absorbed UV photons and find that this is 56 %, on average. This percentage varies with morphological type, with later types having significantly higher UV heating fractions. We find a strong correlation between the UV heating fraction and specific star formation rate and provide a power-law fit. Our models allow us to revisit the IRX-AFUV relations, and derive these quantities directly within a self-consistent framework. We calibrate this relation for different bins of NUV-r colour and provide simple relations to relate these parameters. We investigated the robustness of our method and we conclude that the derived parameters are reliable within the uncertainties which are inherent to the adopted SED model. This calls for a deeper investigation on how well extinction and attenuation can be determined through panchromatic SED modelling.