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Fig. 3

image

a) Example of a spectral fit with fado of the star-forming region a in the low-metallicity BCD CGCG 007-025 (cf. e.g., Guseva et al. 2007). The SDSS spectrum of the source, corrected for Galactic extinction (orange curve), reveals intense nebular emission with a Hα equivalent width of ~2000 Å and strong contamination by nebular continuum emission, as apparent from the complete absence of stellar absorption features and the visible Paschen jump at 8207 Å. The best-fitting synthetic SED (open-blue) is composed of stellar and nebular continuum emission (dark gray and red, respectively). b) Residuals between fit and observed spectrum, with the shaded area and the dashed curve delineating, respectively, the ±1σ and ±3σ error spectrum. c) Luminosity fraction at the normalization wavelength (6490 Å) and d) stellar mass fraction of the SSPs composing the best-fitting population vector as a function of their age. The color-coding depicts the metallicity and the vertical bars ±1σ uncertainties. The thin-gray vertical lines connecting both diagrams correspond to the ages of the SSPs in the used library. The light-blue shaded area in both panels shows an Akima-smoothed (Akima 1970) version of the SSP contributions, giving in panel d) a schematic illustration of the star formation history. The electron temperature Te and density ne computed by fado from emission lines label the upper part of panel a), together with the probability π of the spectrum to fall in the locus of SF, composite, LINER and Seyfert galaxies in BPT diagrams. Details on the meaning of the labels beneath the four panels are provided in the text. Panels c) and d) are shown without errors bars for the sake of better visibility.

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