Dust-to-gas Ratio in the Extremely Metal-poor Galaxy I Zw 18

Herrera-Camus, Rodrigo, Fisher, David B., Bolatto, Alberto D., Leroy, Adam K., Walter, Fabian, Gordon, Karl. D., Roman-Duval, Julia, Donaldson, Jessica, Meléndez, Marcio, & Cannon, John M.
2012, The Astrophysical Journal, 752, 112


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 Spitzer, 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 → 0 transition. We use dust emission models to derive a dust mass upper limit of only M dust <= 1.1 × 104 M ⊙ (3σ limit). This upper limit is driven by the non-detection at 160 μm, and it is a factor of 4-10 times smaller than previous estimates (depending on the model used). We also estimate an upper limit to the total dust-to-gas mass ratio of M Dust/M gas <= 5.0 × 10-5. If a linear correlation between the dust-to-gas mass ratio and metallicity (measured as O/H) were to hold, we would expect a ratio of 3.9 × 10-4. We also show that the infrared spectral energy distribution is similar to that of starbursting systems.

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Copyright © 2012 Karl D. Gordon All Rights Reserved