Spatially resolved dust emission of extremely metal poor galaxies

TL;DR

This study investigates the infrared spectral energy distributions of star-forming regions in extremely metal poor galaxies, revealing distinct dust properties and heating mechanisms compared to higher metallicity galaxies.

Contribution

It provides the first spatially resolved IR SED analysis of EMP galaxies, showing their unique dust temperatures, emissivity, and the link between dust heating and young star surface densities.

Findings

EMP regions have higher f70um/f160um ratios than higher metallicity galaxies.

Dust temperatures in EMP regions are higher, with a significant warm dust component.

Far-IR colors correlate with young star surface densities, not stellar mass.

Abstract

We present infrared (IR) spectral energy distributions (SEDs) of individual star-forming regions in four extremely metal poor (EMP) galaxies with metallicity Z around Zsun/10 as observed by the Herschel Space Observatory. With the good wavelength coverage of the SED, it is found that these EMP star-forming regions show distinct SED shapes as compared to those of grand design Spirals and higher metallicity dwarfs: they have on average much higher f70um/f160um ratios at a given f160um/f250um ratio; single modified black-body (MBB) fittings to the SED at \lambda >= 100 um still reveal higher dust temperatures and lower emissivity indices compared to that of Spirals, while two MBB fittings to the full SED with a fixed emissivity index (beta = 2) show that even at 100 um about half of the emission comes from warm (50 K) dust, in contrast to the cold (~20 K) dust component. Our spatially resolved images further reveal that the far-IR colors including f70um/f160um, f160um/f250um and f250um/f350um are all related to the surface densities of young stars as traced by far-UV, 24 um and SFRs, but not to the stellar mass surface densities. This suggests that the dust emitting at wavelengths from 70 um to 350 um is primarily heated by radiation from young stars.