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Astron. Astrophys. 360, 911-934 (2000)

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The evolution of the color gradients of early-type cluster galaxies *

R.P. Saglia 1, C. Maraston 1, L. Greggio 1,2, R. Bender 1 and B. Ziegler 3

1 Universitätssternwarte, Scheinerstrasse 1, 81679 München, Germany
2 Osservatorio Astronomico, Via Ranzani 1, 40127 Bologna, Italy
3 Universitätssternwarte, Geismarlandstrasse 11, 37083 Göttingen

Received 10 December 1999 / Accepted 4 July 2000


We investigate the origin of color gradients in cluster early-type galaxies to probe whether pure age or pure metallicity gradients can explain the observed data in local and distant ([FORMULA]) samples. We measure the surface brightness profiles of the 20 brightest early-type galaxies of CL0949+44 (hereafter CL0949) at redshift z=0.35-0.38 from HST WF2 frames taken in the filters F555W, F675W, F814W. We determine the color profiles [FORMULA], [FORMULA], and [FORMULA] as a function of the radial distance r in arcsec, and fit logarithmic gradients in the range -0.2 to 0.1 mag per decade. These values are similar to what is found locally for the colors [FORMULA], [FORMULA], [FORMULA] which approximately match the [FORMULA], [FORMULA], [FORMULA] at redshift [FORMULA]. We analyse the results with up to date stellar population models. We find that passive evolution of metallicity gradients ([FORMULA] dex per radial decade) provides a consistent explanation of the local and distant galaxies' data. Invoking pure age gradients (with fixed metallicity) to explain local color gradients produces too steep gradients at redshifts [FORMULA]. Pure age gradients are consistent with the data only if large present day ages [FORMULA] Gyr are assumed for the galaxy centers.

Key words: galaxies: elliptical and lenticular, cD – galaxies: kinematics and dynamics – galaxies: abundances – galaxies: formation

* Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

Send offprint requests to: R.P. Saglia (saglia@usm.uni-muenchen.de)

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© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000