The identification of dust heating mechanisms in nearby galaxies using Herschel 160/250 and 250/350 micron surface brightness ratios

TL;DR

This study investigates the dust heating mechanisms in nearby galaxies by analyzing Herschel infrared surface brightness ratios and their relation to star-forming regions and older stars, revealing diverse heating sources.

Contribution

It provides the first detailed comparison of dust heating sources across multiple galaxies using Herschel data, highlighting the variability in dust heating mechanisms.

Findings

Dust heated by star-forming regions dominates at <=160 microns in some galaxies.

Older stellar populations primarily heat dust at >=250 microns in others.

In some cases, both stellar populations contribute equally to dust heating.

Abstract

We examined variations in the 160/250 and 250/350 micron surface brightness ratios within 24 nearby (<30 Mpc) face-on spiral galaxies observed with the Herschel Space Observatory to identify the heating mechanisms for dust emitting at these wavelengths. The analysis consisted of both qualitative and quantitative comparisons of the 160/250 and 250/350 micron ratios to H alpha and 24 micron surface brightnesses, which trace the light from star forming regions, and 3.6 micron emission, which traces the light from the older stellar populations of the galaxies. We find broad variations in the heating mechanisms for the dust. In one subset of galaxies, we found evidence that emission at <=160 microns (and in rare cases potentially at <=350 microns) originates from dust heated by star forming regions. In another subset, we found that the emission at >=250 microns (and sometimes at >=160 microns) originates from dust heated by the older stellar population. In the rest of the sample, either the results are indeterminate or both of these stellar populations may contribute equally to the global dust heating. The observed variations in dust heating mechanisms does not necessarily match what has been predicted by dust emission and radiative transfer models, which could lead to overestimated dust temperatures, underestimated dust masses, false detections of variability in dust emissivity, and inaccurate star formation rate measurements.