Evolution of dust extinction curves in galaxy simulation
  To understand the evolution of extinction curve, we calculate the dust
evolution in a galaxy using smoothed particle hydrodynamics simulations
incorporating stellar dust production, dust destruction in supernova shocks,
grain growth by accretion and coagulation, and grain disruption by shattering.
The dust species are separated into carbonaceous dust and silicate. The
evolution of grain size distribution is considered by dividing grain population
into large and small gains, which allows us to estimate extinction curves. We
examine the dependence of extinction curves on the position, gas density, and
metallicity in the galaxy, and find that extinction curves are flat at $t
\lesssim 0.3$ Gyr because stellar dust production dominates the total dust
abundance. The 2175 \AA\ bump and far-ultraviolet (FUV) rise become prominent
after dust growth by accretion. At $t \gtrsim 3$ Gyr, shattering works
efficiently in the outer disc and low density regions, so extinction curves
show a very strong 2175 \AA\ bump and steep FUV rise. The extinction curves at
$t\gtrsim 3$ Gyr are consistent with the Milky Way extinction curve, which
implies that we successfully included the necessary dust processes in the
model. The outer disc component caused by stellar feedback has an extinction
curves with a weaker 2175 \AA\ bump and flatter FUV slope. The strong
contribution of carbonaceous dust tends to underproduce the FUV rise in the
Small Magellanic Cloud extinction curve, which supports selective loss of small
carbonaceous dust in the galaxy. The snapshot at young ages also explain the
extinction curves in high-redshift quasars.
