This is the fourth paper in a series studying star formation rates , stellar components , metallicities , and star formation histories of a blue compact galaxy ( BCG ) sample .
Using H \alpha , [ O ii ] \lambda 3727 , infrared ( IR ) , radio ( 1.4 GHz ) luminosities and neutral hydrogen ( H i ) gas masses , we estimated star formation rates and gas depletion timescales of 72 star-forming BCGs .
The star formation rates of the BCGs in our sample span nearly four orders of magnitude , from approximately 10 ^ { -2 } to 10 ^ { 2 } M _ { \odot } yr ^ { -1 } , with a median star formation rate of about 3 M _ { \odot } yr ^ { -1 } .
The typical gas depletion timescale of BCGs is about one billion years .
Star formation could be sustained at the current level only on a timescale significantly lower than the age of the universe before their neutral gas reservoir is completely depleted .

To assess the possible systematic differences among different star formation rate indicators , we compared the star formation rates derived from H \alpha , [ O ii ] \lambda 3727 , IR , and radio luminosities , and investigated the effects from underlying stellar absorption and dust extinction .
We found that subtracting underlying stellar absorption is very important to calculate both dust extinction and star formation rate of galaxies .
Otherwise , the intrinsic extinction will be overestimated , the star formation rates derived from [ O ii ] \lambda 3727 and H \alpha will be underestimated ( if the underlying stellar absorption and the internal extinction were not corrected from the observed luminosity ) or overestimated ( if an overestimated internal extinction were used for extinction correction ) .
After both the underlying stellar absorption and the dust extinction were corrected , a remarkably good correlation emerges among H \alpha , [ O ii ] \lambda 3727 , IR and radio star formation rate indicators .
Finally , we find a good correlation between the measured star formation rate and the absolute blue magnitude , metallicity , interstellar extinction of BCGs .
Our results indicate that faint , low-mass BCGs have lower star formation rates .