Herschel photometric observations of the nearby low metallicity irregular galaxy NGC 6822

TL;DR

This study uses Herschel observations to analyze dust heating and properties in the low-metallicity galaxy NGC 6822, revealing variations in dust temperature and mass depending on dust composition models.

Contribution

First Herschel images of NGC 6822 are used to study dust heating and properties, highlighting the impact of dust composition on mass estimates.

Findings

The 250/500 micron ratio correlates with 24 micron surface brightness.

HII regions exhibit warmer dust temperatures than less active regions.

Dust mass estimates vary significantly with dust composition assumptions.

Abstract

We present the first Herschel PACS and SPIRE images of the low-metallicity galaxy NGC6822 observed from 70 to 500 mu and clearly resolve the HII regions with PACS and SPIRE. We find that the ratio 250/500 is dependent on the 24 mu surface brightness in NGC6822, which would locally link the heating processes of the coldest phases of dust in the ISM to the star formation activity. We model the SEDs of some regions HII regions and less active regions across the galaxy and find that the SEDs of HII regions show warmer ranges of dust temperatures. We derive very high dust masses when graphite is used in our model to describe carbon dust. Using amorphous carbon, instead, requires less dust mass to account for submm emission due to its lower emissivity properties. This indicates that SED models including Herschel constraints may require different dust properties than commonly used.