%0 Generic %1 mcconnell2015radial %A McConnell, Nicholas J. %A Lu, Jessica R. %A Mann, Andrew W. %D 2015 %K absorption imf radial trends %T Radial Trends in IMF-Sensitive Absorption Features in Two Early-Type Galaxies: Evidence for Abundance-Driven Gradients %U http://arxiv.org/abs/1506.07880 %X We have observed two massive early-type galaxies with Keck/LRIS and measured radial gradients in the strengths of stellar absorption features from 4000-5500 \AA$\,$ and 8000-10,000 \AA. We present spatially resolved measurements of the dwarf-sensitive spectral indices NaI (8190 \AA) and Wing-Ford FeH (9915 \AA), as well as indices for species of H, C$_2$, CN, Mg, Ca, TiO, and Fe. Our measurements show a metallicity gradient in both objects, and Mg/Fe consistent with uniform $\alpha$-enhancement, matching widely observed trends for massive early-type galaxies. The NaI index and the CN$_1$ index at 4160 \AA$\,$ exhibit significantly steeper gradients, with a break at $r 0.1 r_eff$ ($r 300$ pc). Inside this radius NaI and CN$_1$ increase sharply toward the galaxy center, relative to other indices. We interpret this trend as a rapid central rise in Na/Fe and N/Fe. In contrast, the FeH index exhibits a marginal decrease toward the galaxy center, relative to Fe. Our investigation is among the first to track FeH as a function of radius, and to demonstrate discrepant behavior between NaI and FeH. We suggest that a shallow gradient in FeH and steep, broken NaI profile reflect unique abundance patterns rather than a gradient in the stellar initial mass function.

@misc{mcconnell2015radial, abstract = {We have observed two massive early-type galaxies with Keck/LRIS and measured radial gradients in the strengths of stellar absorption features from 4000-5500 \AA$\,$ and 8000-10,000 \AA. We present spatially resolved measurements of the dwarf-sensitive spectral indices NaI (8190 \AA) and Wing-Ford FeH (9915 \AA), as well as indices for species of H, C$_2$, CN, Mg, Ca, TiO, and Fe. Our measurements show a metallicity gradient in both objects, and Mg/Fe consistent with uniform $\alpha$-enhancement, matching widely observed trends for massive early-type galaxies. The NaI index and the CN$_1$ index at 4160 \AA$\,$ exhibit significantly steeper gradients, with a break at $r \sim 0.1 r_{\rm eff}$ ($r \sim 300$ pc). Inside this radius NaI and CN$_1$ increase sharply toward the galaxy center, relative to other indices. We interpret this trend as a rapid central rise in [Na/Fe] and [N/Fe]. In contrast, the FeH index exhibits a marginal decrease toward the galaxy center, relative to Fe. Our investigation is among the first to track FeH as a function of radius, and to demonstrate discrepant behavior between NaI and FeH. We suggest that a shallow gradient in FeH and steep, broken NaI profile reflect unique abundance patterns rather than a gradient in the stellar initial mass function.}, added-at = {2015-06-29T09:47:24.000+0200}, author = {McConnell, Nicholas J. and Lu, Jessica R. and Mann, Andrew W.}, biburl = {https://www.bibsonomy.org/bibtex/28bfacfa32c53c6c2df890eb45f3c3fe4/miki}, description = {[1506.07880] Radial Trends in IMF-Sensitive Absorption Features in Two Early-Type Galaxies: Evidence for Abundance-Driven Gradients}, interhash = {07eebef4caa06b223f33675efa5d8afe}, intrahash = {8bfacfa32c53c6c2df890eb45f3c3fe4}, keywords = {absorption imf radial trends}, note = {cite arxiv:1506.07880Comment: 16 page body + 7 page appendix + references. Includes 18 figures. Submitted to ApJ}, timestamp = {2015-06-29T09:47:24.000+0200}, title = {Radial Trends in IMF-Sensitive Absorption Features in Two Early-Type Galaxies: Evidence for Abundance-Driven Gradients}, url = {http://arxiv.org/abs/1506.07880}, year = 2015 }