Stellar Population and Elemental Abundance Gradients of Early-type Galaxies

Abstract

The evolution of galaxies is imprinted in their stellar populations. Several stellar population properties in massive early-type galaxies have been shown to correlate with intrinsic galaxy properties like the galaxy's central velocity dispersion, suggesting that stars formed in an initial collapse of gas (z~2). However, stellar populations change as a function of galaxy radius, and it is not clear how local gradients of individual galaxies are influenced by global galaxy properties and galaxy environment. In this paper, we study the stellar populations of eight early-type galaxies as a function of radius. We use optical spectroscopy (~4000-8600 Å) and full-spectral fitting to measure stellar population age, metallicity, IMF slope, and nine elemental abundances (O, Mg, Si, Ca, Ti, C, N, Na, Fe) out to 1 R_e for each galaxy individually. We find a wide range of properties, with ages ranging from 3-13 Gyr. Some galaxies have a radially constant, Salpeter-like IMF, and other galaxies have a super-Salpeter IMF in the center, decreasing to a sub-Salpeter IMF at ~0.5 R_e. We find a global correlation of the central [Z/H] to the central IMF and the radial gradient of the IMF for the eight galaxies, but local correlations of the IMF slope to other stellar population parameters hold only for subsets of the galaxies in our sample. Some elemental abundances also correlate locally with each other within a galaxy, suggesting a common production channel. Those local correlations appear only in subsets of our galaxies indicating variations of the stellar content among different galaxies.

20 pages, 11 figures, 4 tables (37 pages, 17 figures, 6 tables incl. Appendix). Accepted for publication in ApJ

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