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D.R. Silva, H. Kuntschner (European Southern Observatory)
Extensive efforts over the last 15 years to determine mean stellar age and metallicity in nearby ellipticals have been frustrated by the inherent age-metallicity degeneracy in most optical colors and line indices. In principle, near-IR colors and line indices, although harder to determine, are nearly age independent, making them more robust metallicity indicators. To better quantify this assertion, we are measuring JHK color gradients and K-band (Ca I, Na I, and the CO bandhead) spectral index gradients in Fornax ellipticals, using SOFI at the ESO NTT 3.5m and ISAAC at the ESO UT1/Antu 8.2m telescopes, respectively. Here, our first results for NGC 1404 are presented. Our K-band index measurements are compared to the radial optical Mg b index measurements from Kuntschner (2000). Within the inner 10 arcsecs, we find that: (1) all three near-IR indices become weaker with increasing radius; (2) the Ca I (2.207 \mum) and CO (2.296 \mum) to Mg b index ratios are roughly constant with radius; (3) the Na I (2.207 \mum) to Mg b ratio decreases with radius; and (4) J--H and H--K colors are essentially constant with radius. Further analysis will be presented at the meeting. Our next VLT observing run is scheduled for November 2002 - we hope to present results for more ellipticals at the meeting.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.