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Fig. 10


Star-formation histories of the nucleus, bulge, ring, and disk regions. The black dots correspond to the coloured dots in Fig. 9. The locations of the horizontal blue, green, and red lines indicate the mass fraction of the young ( <1 Gyr), intermediate-old (1–3 Gyr), and old ( >3 Gyr) stellar populations, respectively, calculated by adding the contributions from individual templates (black dots). The horizontal dashed lines indicate the formal errors in the mass fractions, deduce by treating each different azimuthal aperture spectrum as an independent probe of the bulge, ring, and disk regions. For the nucleus, errors should be taken to be similar to those reported for the bulge regions, which are similarly dominated by old stellar populations. We note that the disk measurements are very robust, whereas stochastic effects such as the presence of different numbers of HII regions contribute to the larger errors in the stellar-population analysis for the ring region.

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