4 Data reduction

  The spectroscopic data were reduced with the MIDAS package LONG. The spectra were flux calibrated and corrected for foreground reddening using the method described by Contini et al. (1995, hereafter Paper I).

In order to extract individual spectra of all (nuclear and extranuclear) emission-line regions for each galaxy spectrum, we plotted the spatial distribution of the H$\alpha$ emission line along the slit. We then identified distinct regions of emission and measured their dimension and position along the slit by fitting multi-Gaussian profiles to the H$\alpha$ spatial distribution.

We extracted one-dimensional elementary spectra by adding the columns (spatial dimension) corresponding to the dimension of each emission-line region estimated above. One can note at this stage that 42 galaxies do not have any extra-nuclear emission-line region along the slit (i.e. along the bar). The elementary spectra were cleaned of radiation events ("cosmic rays") before further analysis.

For measuring all the line parameters (fluxes, FWHM and equivalent widths), and for determining the internal reddening ($c_{\rm H\beta}$), we again followed the method described in Paper I. For the latter determination, we adopted Case B of Balmer decrement (I(H$\alpha$)/I(H$\beta$) = 2.85) for classical HII regions, and Case A (I(H$\alpha$)/I(H$\beta$) = 3.10) for AGNs.

We also estimated the continuum flux density, $f_{\lambda}$, of the individual regions in three spectral bands labeled B ($\lambda_{\rm c}$ = 4200 Å and $\Delta \lambda$ = 300 Å), V ($\lambda_{\rm c}$ = 5400 Å and $\Delta \lambda$ = 300 Å) and R ($\lambda_{\rm c}$ = 6800 Å and $\Delta \lambda$ = 200 Å) very close to Johnson's photometric system. In order to obtain the continuum values in a consistent and objective manner, we measured the spectra with an automated algorithm. We chose the wavelength range of the spectral bands in such a way as to exclude the regions containing emission lines.

The measured emission lines are given in Table 4. The galaxy Markarian number is given in Col. 1. The label and code for the position of the emission-line regions (1 = nuclear, 0 = extranuclear) are given in Cols. 2 and 3. The distance of the extranuclear regions from the nucleus, and the diameter of all regions, expressed in arcsec, are given in Cols. 4 and 5. The observed fluxes $F(\lambda)$ and equivalent widths of H$\beta$, H$\alpha$ (both corrected for Balmer absorption), [OIII]$\lambda$4959, [OIII]$\lambda$5007, [NII]$\lambda$6548, [NII]$\lambda$6583, [SII]$\lambda$6716 and [SII]$\lambda$6731 are listed in Cols. 6 to 21.

The continuum measurements are listed in Table 5. The galaxy Markarian number is given in Col. 1. The magnitudes integrated along the slit (m_B, m_V and m_R) are given in Cols. 3, 4 and 5, where $m_{\lambda} = -2.5\log(f_{\lambda}) - 5\log(\lambda) - 2.41$, with $f_{\lambda}$ in units of erg s^-1 cm^-2 Å^-1 and $\lambda$ in Å (Mazzarella & Boroson 1993). We further used the continuum magnitudes to define two color indices: B-V = m_B - m_V and V-R = m_V - m_R which are reported in Cols. 6 and 7. Tables 4 and 5 are given in electronic form only.

  

Figure 1: Diagnostic diagrams, adapted from Veilleux & Osterbrock (1987), showing a) log([OIII]$\lambda$5007/H$\beta$) vs. log([NII]$\lambda$6583/H$\alpha$) and b) log([OIII]$\lambda$5007/H$\beta$) vs. log([SII]$\lambda\lambda$6716,6731/H$\alpha$). The symbols are: filled squares = starburst nuclei, open squares = extranuclear HII regions, filled circles = Seyfert 2 nuclei and triangle = objects with an ambiguous classification (HII or LINER, see text). In each diagram two curves (solid lines) separate the emission-line regions in three groups: starburst galaxies or HII regions (lower left), Seyfert 2 galaxies (upper right) and LINERs (lower right). The dashed curve denotes the theoretical models of disk HII regions of McCall et al. (1985). Also shown is the photoionization model of Shields & Kennicutt (1995) (dotted curve)

   Table 4: Measured spectrophotometric data. Observed intensities and equivalent widths of emission lines (available in electronic form only)

   Table 5: Measured spectrophotometric data. Magnitudes and color indices of the spectral continuum (available in electronic form only)