We analyze the star formation history ( SFH ) of the Galactic disk by using an infall model .
Based on the observed SFH of the Galactic disk , we first determine the timescales of the gas infall into the Galactic disk ( t _ { in } ) and that of the gas consumption to form stars ( t _ { sf } ) .
Since each of the two timescales does not prove to be determined independently from the SFH , we first fix t _ { sf } .
Then , t _ { in } is determined so that we minimize \chi ^ { 2 } .
Consequently , we choose three parameter sets : ( t _ { sf } { [ Gyr ] } , t _ { in } { [ Gyr ] } ) = ( 6.0 , 23 ) , ( 11 , 12 ) , and ( 15 , 9.0 ) , where we set the Galactic age as 15 Gyr .
All of the three cases predict almost identical star formation history .
Next , we test the intermittency ( or variability ) of the star formation rate ( SFR ) along with the smooth SFH suggested from the infall model .
The large value of the \chi ^ { 2 } statistic supports the violent time-variation of the SFH .
If we interpret the observed SFH with smooth and variable components , the amplitude of the variable component is comparable to the smooth component .
Thus , intermittent SFH of the Galactic disk is strongly suggested .
We also examined the metallicity distribution of G-dwarfs .
We found that the true parameter set lies between ( t _ { sf } { [ Gyr ] } , t _ { in } { [ Gyr ] } ) = ( 6 , 23 ) \mbox { and } ( 11 , 12 ) , though we should need a more sophisticated model including the process of metal enrichment within the Galactic halo .