Measuring K-band Spectral Indices in Fornax Ellipticals: First Results

Details Measuring K-band Spectral Indices in Fornax Ellipticals: First Results Measuring K-band Spectral Indices in Fornax Ellipticals: First Results

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aas...201.1415s&link_type=abstract

American Astronomical Society, 201st AAS Meeting, #14.15; Bulletin of the American Astronomical Society, Vol. 34, p.1120

Astronomy and Astrophysics

Astronomy

Scientific paper

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 μ m) and CO (2.296 μ m) to Mg b index ratios are roughly constant with radius; (3) the Na I (2.207 μ m) 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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