We present a newly observed relation between galaxy mass and radial metallicity gradients of early-type galaxies .
Our sample of 51 early-type galaxies encompasses a comprehensive mass range from dwarf to brightest cluster galaxies .
The metallicity gradients are measured out to one effective radius by comparing nearly all of the Lick absorption-line indices to recent models of single stellar populations .
The relation shows very different behavior at low and high masses , with a sharp transition being seen at a mass of \sim 3.5 \times 10 ^ { 10 } M _ { \odot } ( velocity dispersion of \sim 140 km s ^ { -1 } , M _ { B } \sim - 19 ) .
Low-mass galaxies form a tight relation with mass , such that metallicity gradients become shallower with decreasing mass and positive at the very low-mass end .
Above the mass transition point several massive galaxies have steeper gradients , but a clear downturn is visible marked by a broad scatter .
The results are interpreted in comparison with competing model predictions .
We find that an early star-forming collapse could have acted as the main mechanism for the formation of low-mass galaxies , with star formation efficiency increasing with galactic mass .
The high-mass downturn could be a consequence of merging and the observed larger scatter a natural result of different merger properties .
These results suggest that galaxies above the mass threshold of \sim 3.5 \times 10 ^ { 10 } M _ { \odot } might have formed initially by mergers of gas-rich disk galaxies and then subsequently evolved via dry merger events .
The varying efficiency of the dissipative merger-induced starburst and feedback processes have shaped the radial metallicity gradients in these high-mass systems .