All Figures

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{ms3793.f1}\end{figure}$ Figure 1: Examples of two fits using our code to measure the equivalent widths and fluxes of H $\beta$ ( top panels) and H $\alpha$ ( bottom panels). The left and right figures are for spectra with signal-to-noise ratio in g-band of 5.9 and 12.4, respectively. We also show the equivalent widths (EW) in Å and signal-to-noise ratio ( S/N) of the measured emission lines.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{ms3793.f2}\end{figure}$ Figure 2: Results of the simulations for a spectral dispersion of 1.0 Å and typical noise. The input equivalent widths are based on the results of the spectrophotometric model of Barbaro & Poggianti (1997) for different spectral types: Sa, Sb, Sc, Sd and "Extreme'' case with constantly increasing star formation rates. These equivalent widths are compared with the values recovered by our code. The large squares are the mean values of the output equivalent widths, with the error bars showing their dispersion.
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In the text

$\begin{figure} \par\includegraphics[width=4.9cm,clip]{ms3793.f3}\end{figure}$ Figure 3: Emission line diagnostic diagram to separate normal galaxies from galaxies hosting an AGN. The points represent the 10 822galaxies from the SDSS that have been selected according to the criteria described in Sect. 2.1. Solid line: the curve of Heckman & Kauffmann (2003); all the galaxies below that curve (9840 objects) constitute our sample of normal galaxies. Dot-dashed line: the theoretical curve of Kewley et al. (2001) above which galaxies are dominated by an AGN; dashed line: empirical lower bound of normal galaxies (see Sect. 2.2).
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{ms3793.f4}\end{figure}$ Figure 4: Histograms of general properties of our sample of normal galaxies.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{ms3793.f5}\end{figure}$ Figure 5: Some global properties of the galaxies of our sample as a function of their "spectral type''. The top number on the right is the total number of data points (including a few individual points that may lie outside the panel frame). Below are: the value of Kendall's $\tau _{\rm K}$ , then the associated probability and finally the Spearman rank correlation coefficient $r_{\rm S}$ (see Sect. 2.3).
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In the text

$\begin{figure} \par\includegraphics[width=16.3cm,clip]{ms3793.f6}\end{figure}$ Figure 6: The relation between log (H $\alpha$ /H $\beta$ ) and various properties of the galaxies. The meaning of the numbers in the upper right is the same as in Fig. 5. The thick curve represents the median value of log (H $\alpha$ /H $\beta$ ). The thin curves delimit the zone containing 80% of the data points (see Sect. 3.1).
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In the text

$\begin{figure} \par\includegraphics[width=5cm,clip]{ms3793.f7}\end{figure}$ Figure 7: The relation between the metallicity indicator [N II] $\lambda$ 6584/H $\alpha$ and the absolute magnitude $M_{\rm B}$ in the galaxies of our sample. Same layout as for the panels in Fig. 6.
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In the text

$\begin{figure} \par\includegraphics[width=16.6cm,clip]{ms3793.f8}\end{figure}$ Figure 8: Same diagrams as in Fig. 6 except that the ordinate is $C({\rm H}\beta )$ /([N II] $\lambda$ 6584/H $\alpha$ )^0.9 instead of log (H $\alpha$ /H $\beta$ ) (see Sect. 3.3).
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In the text

$\begin{figure} \par\includegraphics[width=10.4cm,clip]{ms3793.f9}\end{figure}$ Figure 9: $L({\rm H}\beta )_{\rm corr}$ versus M(r) ( left) and D(4000)vesus M(r). Same layout as Fig. 5.
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In the text

$\begin{figure} \par\includegraphics[width=4.8cm,clip]{ms3793.f10}\end{figure}$ Figure 10: Histogram of the values of the Balmer extinction at H $\beta$ , $C(\mbox{H$\beta$ })$ in our sample of galaxies.
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In the text

$\begin{figure} \par\includegraphics[width=4.9cm,clip]{ms3793.f11}\end{figure}$ Figure 11: The relation between EW(H $\beta$ )and EW(H $\alpha$ ) in our sample of galaxies. The layout of the figure is the same as for Fig. 5.
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In the text

$\begin{figure} \par\includegraphics[width=10.4cm,clip]{ms3793.f12}\end{figure}$ Figure 12: Galaxies from our sample detected by IRAS (see Sect. 5). Plots of log (H $\alpha$ /H $\beta$ ) vs. log $L(\rm FIR)$ (panel a)) and log $L(\mbox{H$\beta$ })$ (corrected for Balmer extinction) vs. log $L(\rm FIR)$ (panel b)).
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In the text

$\begin{figure} \par\includegraphics[width=16.6cm,clip]{ms3793.f13}\end{figure}$ Figure 13: Same diagrams as in Fig. 6, with the galaxies detected by IRAS represented with large circles.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{ms3793.f1}\end{figure}$	Figure 1: Examples of two fits using our code to measure the equivalent widths and fluxes of H $\beta$ ( top panels) and H $\alpha$ ( bottom panels). The left and right figures are for spectra with signal-to-noise ratio in g-band of 5.9 and 12.4, respectively. We also show the equivalent widths (EW) in Å and signal-to-noise ratio ( S/N) of the measured emission lines.
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$\begin{figure} \par\includegraphics[width=12cm,clip]{ms3793.f4}\end{figure}$	Figure 4: Histograms of general properties of our sample of normal galaxies.
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$\begin{figure} \par\includegraphics[width=16.3cm,clip]{ms3793.f6}\end{figure}$	Figure 6: The relation between log (H $\alpha$ /H $\beta$ ) and various properties of the galaxies. The meaning of the numbers in the upper right is the same as in Fig. 5. The thick curve represents the median value of log (H $\alpha$ /H $\beta$ ). The thin curves delimit the zone containing 80% of the data points (see Sect. 3.1).
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$\begin{figure} \par\includegraphics[width=5cm,clip]{ms3793.f7}\end{figure}$	Figure 7: The relation between the metallicity indicator [N II] $\lambda$ 6584/H $\alpha$ and the absolute magnitude $M_{\rm B}$ in the galaxies of our sample. Same layout as for the panels in Fig. 6.
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$\begin{figure} \par\includegraphics[width=16.6cm,clip]{ms3793.f8}\end{figure}$	Figure 8: Same diagrams as in Fig. 6 except that the ordinate is $C({\rm H}\beta )$ /([N II] $\lambda$ 6584/H $\alpha$ )^0.9 instead of log (H $\alpha$ /H $\beta$ ) (see Sect. 3.3).
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$\begin{figure} \par\includegraphics[width=10.4cm,clip]{ms3793.f9}\end{figure}$	Figure 9: $L({\rm H}\beta )_{\rm corr}$ versus M(r) ( left) and D(4000)vesus M(r). Same layout as Fig. 5.
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$\begin{figure} \par\includegraphics[width=4.8cm,clip]{ms3793.f10}\end{figure}$	Figure 10: Histogram of the values of the Balmer extinction at H $\beta$ , $C(\mbox{H$\beta$ })$ in our sample of galaxies.
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$\begin{figure} \par\includegraphics[width=4.9cm,clip]{ms3793.f11}\end{figure}$	Figure 11: The relation between EW(H $\beta$ )and EW(H $\alpha$ ) in our sample of galaxies. The layout of the figure is the same as for Fig. 5.
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$\begin{figure} \par\includegraphics[width=10.4cm,clip]{ms3793.f12}\end{figure}$	Figure 12: Galaxies from our sample detected by IRAS (see Sect. 5). Plots of log (H $\alpha$ /H $\beta$ ) vs. log $L(\rm FIR)$ (panel a)) and log $L(\mbox{H$\beta$ })$ (corrected for Balmer extinction) vs. log $L(\rm FIR)$ (panel b)).
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$\begin{figure} \par\includegraphics[width=16.6cm,clip]{ms3793.f13}\end{figure}$	Figure 13: Same diagrams as in Fig. 6, with the galaxies detected by IRAS represented with large circles.
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