\begin{table}%t7
\caption{Representative fits to the envelopes of the log~$L_{\scriptsize\ha} - \log~\rm\sigma_{nt}$~distributions for NGC~1530, NGC~3359 and NGC~6951 and for the distribution defined with all the \hii~regions in the three galaxies. The logarithmic \ha~luminosity corresponds to the value given in the calibration catalogue.}\label{tabenvol}
%\centering
\par
\begin{tabular}{lcc}
\hline
\hline
             & Bin & Envelope fit   \\
\hline
    NGC~1530 & 0.15 & log~$L_{\scriptsize\ha} \sim (37.0 \pm 0.3)+(2.0 \pm 0.2)~\log~\rm\sigma_{nt}$   \\
    NGC~3359 & 0.15 & log~$L_{\scriptsize\ha} \sim (37.5 \pm 0.4)+(1.4 \pm 0.7)~\log~ \rm\sigma_{nt}$   \\
    NGC~6951 & 0.15 & log~$L_{\scriptsize\ha} \sim (37.7 \pm 0.4)+(1.2 \pm 0.4)~\log~ \rm\sigma_{nt}$   \\
All galaxies & 0.15 & log~$L_{\scriptsize\ha} \sim (37.4 \pm 0.2)+(1.78 \pm 0.14)~\log~ \rm\sigma_{nt}$   \\
\hline
\end{tabular}
\end{table}