METALLICITY GRADIENTS IN EARLY-TYPE GALAXIES

Narrow-band optical and near-IR images are used to study color gradien ts in elliptical and S0 galaxies. Over 90% of the 23 sample galaxies d isplay gradients in the optical of DELTA(v-y)/DELTA log r=-0.15+/-0.08 (which corresponds to DELTA(B-R)/DELTA log r=-0.09, in agreement with previous broadband studies) and in the near-IR of DELTA(V-K)/DELTA lo g r=-0.27+/-0.14 and DELTA(J-K)/DELTA log r=-0.15+/-0.12. Using an emp irical calibration from the optical colors v-y to Mg2 produces a mean Mg gradient for the sample equivalent to DELTAMg2/DELTA log r=-0.036+/ -0.016 or DELTAMg2/DELTAmu(V)=-0.013+/-0.007. Near-IR colors imply DEL TA[Fe/H]/DELTA log r=-0.48 and core [Fe/H] values between -0.5 and +0. 1 versus halo values near -1.3. A discrepancy exists between optical c olors, influenced by light element abundances (particularly CN), and J -K, which is dominated by the true metallicity as reflected in the mea n giant branch temperature, supporting the hypothesis that the [Mg/Fe] ratio in early-type galaxies differs from other galaxies due to an en hanced Type II SN component at the initial phase of star formation [Wo rthey et al., ApJ, 393, 611 (1992) ]. Gradients in our continuum color , b-y, signals a blue horizontal branch population contribution in the integrated light and warns that finer knowledge of the color evolutio nary history of early-type galaxies will require substantial improveme nts in our Spectroenergy distribution models in order to predict behav ior from the far-UV to the near-IR.