Effects of grain shattering by turbulence on extinction curves in
  starburst galaxies
  Dust grains can be efficiently accelerated and shattered in warm ionized
medium (WIM) because of the turbulent motion. This effect is enhanced in
starburst galaxies, where gas is ionized and turbulence is sustained by massive
stars. Moreover, dust production by Type II supernovae (SNe II) can be
efficient in starburst galaxies. In this paper, we examine the effect of
shattering in WIM on the dust grains produced by SNe II. We find that although
the grains ejected from SNe II are expected to be biased to large sizes ($a\ga
0.1 \micron$, where $a$ is the grain radius) because of the shock destruction
in supernova remnants, the shattering in WIM is efficient enough in $\sim 5$
Myr to produce small grains if the metallicity is nearly solar or more. The
production of small grains by shattering steepens the extinction curve. Thus,
steepening of extinction curves by shattering should always be taken into
account for the system where the metallicity is solar and the starburst age is
typically larger than 5 Myr. These conditions may be satisfied not only in
nearby starbursts but also in high redshift ($z>5$) quasars.
