We investigate the extinction curves of young galaxies in which dust is supplied from Type II supernovae ( SNe II ) and/or pair instability supernovae ( PISNe ) .
Since at high redshift ( z > 5 ) , low-mass stars can not be dominant sources for dust grains , SNe II and PISNe , whose progenitors are massive stars with short lifetimes , should govern the dust production .
Here , we theoretically investigate the extinction curves of dust produced by SNe II and PISNe , taking into account reverse shock destruction induced by collision with ambient interstellar medium .
We find that the extinction curve is sensitive to the ambient gas density around a SN , since the efficiency of reverse shock destruction strongly depends on it .
The destruction is particularly efficient for small-sized grains , leading to a flat extinction curve in the optical and ultraviolet wavelengths .
Such a large ambient density as n _ { H } \ga 1 cm ^ { -3 } produces too flat an extinction curve to be consistent with the observed extinction curve for SDSS J1048+4637 at z = 6.2 .
Although the extinction curve is highly sensitive to the ambient density , the hypothesis that the dust is predominantly formed by SNe at z \sim 6 is still allowed by the current observational constraints .
For further quantification , the ambient density should be obtained by some other methods .
Finally we also discuss the importance of our results for observations of high- z galaxies , stressing a possibility of flat extinction curves .