Metallicity Gradient And The Hybrid Formation Scenario For Early-Type   Galaxies
  We present radial gradients of the Lick index Mg2 for 40 early-type galaxies. In plots of Grad(Mg2) versus mass indicators, such as log(sigma), the lower boundary of the points distribution may be populated by galaxies which predominantly formed by monolithic collapse. Galaxies showing flatter gradients at higher masses could represent objects which suffered important merging episodes. Thus, our results support a hybrid formation scenario. To remove possible age effects, we computed metallicity gradients (Grad[Z/H]) using Mg2 and Hbeta indices for an [alpha/Fe]=0.3 single stellar population model. The conclusions remain the same. 
Ricardo L. C. Ogando (1 and 2), Marcio A. G. Maia (2), Cristina   Chiappini (3), Paulo S. S. Pellegrini (2), Ricardo P. Schi...