We measure the strength , frequency , and timescale of tidally triggered star formation at redshift z = 0.08 - 0.38 in a spectroscopically complete sample of galaxy pairs drawn from the magnitude-limited redshift survey of 9,825 Smithsonian Hectospec Lensing Survey ( SHELS ) galaxies with R < 20.3 .
To examine the evidence for tidal triggering , we identify a volume-limited sample of major ( \left| \Delta M _ { R } \right| < 1.75 , corresponding to mass ratio > 1 / 5 ) pair galaxies with M _ { R } < -20.8 in the redshift range z = 0.08 - 0.31 .
The size and completeness of the spectroscopic survey allows us to focus on regions of low local density .
The spectrophotometric calibration enables the use of the the 4000Â Ã Â break ( D _ { n } 4000 ) , the H \alpha specific star formation rate ( SSFR _ { H \alpha } ) , and population models to characterize the galaxies .
We show that D _ { n } 4000 is a useful population classification tool ; it closely tracks the identification of emission line galaxies .
The sample of major pair galaxies in regions of low local density with low D _ { n } 4000 demonstrates the expected anti-correlation between pair-wise projected separation and a set of star formation indicators explored in previous studies .
We measure the frequency of triggered star formation by comparing the SSFR _ { H \alpha } in the volume-limited sample in regions of low local density : 32 \pm 7 \% of the major pair galaxies have SSFR _ { H \alpha } at least double the median rate of the unpaired field galaxies .
Comparison of stellar population models for pair and for unpaired field galaxies implies a timescale for triggered star formation of \sim 300 - 400 Â Myr .