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We examine stellar population gradients in ~100 massive early type galaxiesspanning 180 < sigma* < 370 km/s and M_K of -22.5 to -26.5 mag, observed aspart of the MASSIVE survey (Ma et al. 2014). Using integral-field spectroscopyfrom the Mitchell Spectrograph on the 2.7m telescope at McDonald Observatory,we create stacked spectra as a function of radius for galaxies binned by theirstellar velocity dispersion, stellar mass, and group richness. With excellentsampling at the highest stellar mass, we examine radial trends in stellarpopulation properties extending to beyond twice the effective radius (~2.5R_e). Specifically, we examine trends in age, metallicity, and abundance ratiosof Mg, C, N, and Ca, and discuss the implications for star formation historiesand elemental yields. At a fixed physical radius of 3-6 kpc (the likely size ofthe galaxy cores formed at high redshift) stellar age and [alpha/Fe] increasewith increasing sigma* and depend only weakly on stellar mass, as we mightexpect if denser galaxies form their central cores earlier and faster. If weinstead focus on 1-1.5 R_e, the trends in abundance and abundance ratio arewashed out, as might be expected if the stars at large radius were accreted bysmaller galaxies. Finally, we show that when controlling for \sigmastar, thereare only very subtle differences in stellar population properties or gradientsas a function of group richness; even at large radius internal propertiesmatter more than environment in determining star formation history.

The MASSIVE Survey II: Stellar Population Trends Out to Large Radius in Massive Early Type Galaxies