AGB stars in the Magellanic Clouds - I. The C/M ratio

Regions of different metallicity have been identified in the Magellanic Clouds by using the ratio between Asymptotic Giant Branch stars of spectral type C and M. In the Large Magellanic Cloud the ratio appears to decrease radially while in the Small Magellanic Cloud (SMC) there is no clear trend, reflecting either the large extension of the SMC along the line of sight or a more complex star formation history. The distribution of the C/M ratio is clumpy and corresponds to a spread in [Fe/H] of 0.75 dex in both Clouds. There is an indication of increasing C/M ratio, thus decreasing metallicity, towards the Bridge region connecting the two Clouds.