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8 The H$_\alpha$ catalogue

Table 7 lists the H$_\alpha$ isophotal fluxes and luminosities estimated:
Column 1: Name of the galaxy (Hickson 1982);
Column 2: flux uncorrected for Galactic and Internal Extinction: $f_{\rm iso}$(1) (erg cm-2 s-1);
Column 3: error about $f_{\rm iso}$ (1): $\sigma_{f_{\rm iso}}(1)$(erg cm-2 s-1);
Column 4: luminosity uncorrected for Galactic and Internal Extinction: $L_{\rm
iso}$ (1) (erg s-1);
Column 5: error about $L_{\rm
iso}$ (1): $\sigma_{L_{1}}$ (1) (erg s-1);
Column 6: flux corrected for Galactic Extinction $f_{\rm iso}$ (2) (erg cm-2 s-1);
Column 7: error about $f_{\rm iso}$ (2): $\sigma_{f_{\rm iso}}$ (2) (erg cm-2 s-1);
Column 8: flux corrected for Galactic and Internal Extinction for spiral galaxies: $f_{\rm iso}$ (3) (erg s-1);
Column 9: isophotal area at 1$\sigma$ above the background: $A_{\rm iso}$(arcsec2);
Column 10: S/N ratio computed within the isophotal region defined by the detection threshold.

In Tables 8 and 9 the fluxes are not corrected for Galactic and Internal Extinction. Such corrections can be simply derived from Table 7.

Table 8 lists isophotal corrected and adaptive aperture fluxes:
Column 1: Name of the galaxy (Hickson 1982);
Column 2: isophotal flux $f_{\rm isocor}$ (erg cm-2 s-1);
Column 3: error about $f_{\rm isocor}$: $\sigma_{\rm isocor}$(erg cm-2 s-1);
Column 4: kron flux $f_{\rm Kron}$ (erg cm-2 s-1);
Column 5: error about $f_{\rm Kron}$: $\sigma_{\rm Kron}$(erg cm-2 s-1).

In Table 9 we report the fluxes and luminosities of upper limits:
Column 1: Name of the galaxy (Hickson 1982);
Column 2: flux at 3 $\sigma$ above the background ($f_{3\sigma}$)(erg cm-2 s-1);
Column 3: error about $f_{3\sigma}$: $\sigma$ (erg cm-2 s-1);
Column 4: luminosity at 3 $\sigma$ above the background ($L_{3\sigma}$)(erg s-1);
Column 5: error about $L_{3\sigma}$: $\sigma$ (erg s-1).

We have compared the estimated $f_{\rm iso}$, $f_{\rm isocor}$ and $f_{\rm kron}$ for the detected galaxies by using the Kolmogorov-Smirnov test: we found they are drawn from the same parent population. The distributions of the three different fluxes estimated for the detected galaxies are shown in Fig. 3. In the following we make use of $f_{\rm iso}$ in our considerations unless it is differently specified.

  
\begin{figure}
\includegraphics [width=7.8cm,height=8cm,clip]{flux.ps}\end{figure} Figure 3: Distribution of $f_{\rm iso}$ (solid line), $f_{\rm isocor}$ (dashed line) and $f_{\rm kron}$ (dotted line) (corrected for Galactic Extinction) of the 73 detected galaxies. The width of each bin is 0.5 [10-13 erg cm-2 s-1]

In Fig. 4 the distribution of H$_\alpha$ isophotal luminosity $L_{\rm
iso}$,corrected for Galactic Extinction and uncorrected for Internal Extinction, of the 73 detected galaxies (shaded histogram) is shown. We over-plot also the distribution of H$_\alpha$ upper limits to luminosity for the 22 undetected galaxies (dashed line).

  
\begin{figure}
\includegraphics [width=7.8cm,height=8cm,clip]{luminosita.ps}\end{figure} Figure 4: Distribution of H$_\alpha$ luminosity, corrected for Galactic Extinction, for both the 73 detected galaxies (shaded histogram) and for the 22 upper limits (dashed line). The width of each bin is 0.8 [1040 erg s-1]

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