Dust-to-Gas Ratio in the Extremely Metal Poor Galaxy I ZW 18

TL;DR

This study provides new, more stringent upper limits on the dust mass and dust-to-gas ratio in the extremely metal-poor galaxy I Zw 18, using sensitive infrared and radio observations, challenging previous estimates.

Contribution

It offers the first sensitive measurements of dust content in I Zw 18, establishing lower upper limits and examining the dust-to-gas ratio's relation to metallicity in such a metal-poor galaxy.

Findings

Dust mass upper limit of ≤1.1×10^4 M⊙

Dust-to-gas ratio ≤5.0×10^−5

Infrared SED similar to starburst systems

Abstract

The blue compact dwarf galaxy I Zw 18 is one of the most metal poor systems known in the local Universe (12 + log(O/H) $=$ 7.17). In this work we study I Zw 18 using data from {\it Spitzer}, {\it Herschel Space Telescope} and IRAM Plateau de Bure Interferometer. Our data set includes the most sensitive maps of I Zw 18, to date, in both, the far infrared and the CO $J=1\rightarrow0$ transition. We use dust emission models to derive a dust mass upper limit of only M$_{dust}\leq1.1\times10^4$ M$_{\odot}$ ($3\sigma$ limit). This upper limit is driven by the non-detection at 160 $\mu$m, and it is a factor of 4-10 times smaller than previous estimates (depending upon the model used). We also estimate an upper limit to the total dust-to-gas mass ratio of M$_{Dust}$/M$_{gas}\leq5.0\times10^{-5}$. If a linear correlation between the dust-to-gas mass ratio and metallicity (measure as O/H) were to hold, we would expect a ratio of 3.9$\times10^{-4}$. We also show that the infrared SED is similar to that of starbursting systems.