We present results from the largest CaII triplet line metallicity study of Small Magellanic Cloud ( SMC ) field red giant stars to date , involving 3037 objects spread across approximately 37.5 deg ^ { 2 } , centred on this galaxy .
We find a median metallicity of [ Fe/H ] =-0.99 \pm 0.01 , with clear evidence for an abundance gradient of -0.075 \pm 0.011 dex deg ^ { -1 } over the inner 5 ^ { \circ } .
We interpret the abundance gradient to be the result of an increasing fraction of young stars with decreasing galactocentric radius , coupled with a uniform global age-metallicity relation .
We also demonstrate that the age-metallicity relation for an intermediate age population located 10kpc in front of the NE of the Cloud is indistinguishable from that of the main body of the galaxy , supporting a prior conjecture that this is a stellar analogue of the Magellanic Bridge .
The metal poor and metal rich quartiles of our RGB star sample ( with complementary optical photometry from the Magellanic Clouds Photometric Survey ) are predominantly older and younger than approximately 6Gyr , respectively .
Consequently , we draw a link between a kinematical signature , tentatively associated by us with a disk-like structure , and the upsurges in stellar genesis imprinted on the star formation history of the central regions of the SMC .
We conclude that the increase in the star formation rate around 5-6Gyr ago was most likely triggered by an interaction between the SMC and LMC .