The small grain sizes produced by Type II supernova ( SN II ) models in young , metal-poor galaxies make the appearance of their infrared ( IR ) spectral energy distribution ( SED ) quite different from that of nearby , older galaxies .
To study this effect , we have developed a model for the evolution of dust content and the IR SED of low-metallicity , extremely young galaxies based on ( ) .
We find that , even in the intense ultraviolet ( UV ) radiation field of very young galaxies , small silicate grains are subject to stochastic heating resulting in a broad temperature distribution and substantial MIR continuum emission .
Larger carbonaceous grains are in thermal equilibrium at T \simeq 50 \mbox { - - } 100 K , and they also contribute to the MIR .
We present the evolution of SEDs and IR extinction of very young , low-metallicity galaxies .
The IR extinction curve is also shown .
In the first few Myrs , the emission peaks at \lambda \sim 30 \mbox { - - } 50 \mu m ; at later times dust self-absorption decreases the apparent grain temperatures , shifting the bulk of the emission into the submillimetre band .
We successfully apply the model to the IR SED of SBS 0335 - 052 , a low metallicity ( 1/41 Z _ { \odot } ) dwarf galaxy with an unusually strong MIR flux .
We find the SED , optical properties and extinction of the star forming region to be consistent with a very young ( \mbox { age } \simeq 6.5 \times 10 ^ { 6 } \mbox { yr } ) and compact ( \mbox { radius } \simeq 20 \mbox { pc } ) starburst .
We also predict the SED of another extremely low-metallicity galaxy , I Zw 18 , for future observational tests .
We estimate the FIR luminosity of I Zw 18 to be low as L _ { FIR } \sim 10 ^ { 7 \mbox { - - } 7.5 } L _ { \odot } , depending on the uncertainty of dust mass .
Some prospects for future observations are discussed .