Stellarpopulation synthesis

We used the STARLIGHT code (Cid Fernandes et al. 2005) to fit the spectrum of our galaxies and to understand the distribution in ages and metallicities. It also allows us to subtract the underlying spectrum of older stellar populations to better quantify the numbers of O stars and WR stars.

The fitting of the observed spectra of our galaxies is best illustrated by Figure 30.1, where we show the fit and the corresponding age distribution found for galaxy NGC 2798. Similar fits were produced for all galaxies in the sample.

We find that most galaxies are dominated by young stellar populations, indicating recent bursts of star formation. We also find that an underlying older stellar population is present, indicating that past episodes of star formation occurred. We also recover a very good correlation between the infrared luminosity and the average age of burst, i.e. younger systems are also more luminous.

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Figure 30.1. The optical spectrum of NGC 2798. Upper left: the optical spectrum of NGC 2798 and the corresponding fit. Lower left: the residual spectrum. Lower right: star-formation history (mass-fraction). Upper right: star-formation history (light).

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Figure 30.1. The optical spectrum of NGC 2798. Upper left: the optical spectrum of NGC 2798 and the corresponding fit. Lower left: the residual spectrum. Lower right: star-formation history (mass-fraction). Upper right: star-formation history (light).

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