next previous
Up: Spectroscopic observations of southern galaxies


3 Results

The intensities of the emission lines present in the spectra (obtained with 125 Å mm-1 dispersion) of the nuclear region and of a region located at 87$\hbox{$^{\prime\prime}$}$ towards the NE on the major axis, were derived fitting Gaussian curves to their profiles. In the nuclear spectrum the H$\beta$emission line is affected by the underlying H$\beta$ absorption line, so Gaussian curves were interactively fitted to determine the absorption component and to isolate the H$\beta$ emission. This procedure was verified by adding both, emission and absorption components, to reproduce the original profile. The internal reddening correction was carried out using the interstellar extinction curves given by Seaton (1979), assuming that the optical properties of the dust in NGC 2442 are similar to those in the Galaxy. The logarithmic extinction c, at H$\beta$, was obtained using for the intrinsic ratio H$\alpha$/H$\beta$ the values 3.1 and 2.85 for the nucleus and for the region at the NE, respectively (Veilleux & Osterbrock 1987). The measured and corrected line intensities $F\lambda$ and $I\lambda$, relative to H$\beta$ = 1.00, are listed in Table 2 as well as the errors. These errors were estimated from the noise level around each line. The values of c and of the corrected H$\beta$ flux are given at the bottom of the table.


  
Table 2: Line Intensities relative to H$\beta$

\begin{tabular}
{\vert ccccccc\vert}
\noalign{\smallskip}
\hline
\noalign{\small...
 ... $I{\beta} ^c$\space & &$-$13.69& & &$-$13.60& \\ \noalign{}
\hline\end{tabular}
a $\sigma$ is the absolute error of the $F\lambda/F\beta$ ratio,
b c is the logarithmic extinction at H$\beta$,
c $I{\beta}$ is the flux corrected for reddening in erg cm-2 s-1.

The mean radial velocities of all the spectra were derived measuring the centroids of Gaussian profiles centered on the emission lines [O I] $\lambda$6300, [N II] $\lambda\lambda$6548, 6584, H$\alpha$, and [S II] $\lambda\lambda$6717, 6731 in the spectra obtained with a dispersion of 32 Å mm-1. The errors are estimated to be 3 to 26 $\rm \, km\, s^{-1}$, depending on the signal-to-noise ratio. The optical heliocentric radial velocities are shown in Fig. 5 superposed on the CO velocity field as obtained by Bajaja et al. (1995).

  
\begin{figure}
\resizebox {8.8cm}{!}{\includegraphics{eb8111f2.eps}}
\\ end{figure} Figure 2: Nuclear spectrum of NGC 2442. Dispersion 32 Å mm-1

The spectrum at the nuclear region of the galaxy (Fig. 2) shows two velocity components, on each of the prominent lines, with approximately the same intensity and a separation of about 145 $\rm \, km\, s^{-1}$.


next previous
Up: Spectroscopic observations of southern galaxies

Copyright The European Southern Observatory (ESO)