Astronomy & Astrophysics

All Figures

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig1.eps} \end{figure}$ Figure 1: H II region identification for NGC 1232. In this and in the following charts, derived from R-band FORS1 or FORS2 images, the slitlet numbers for the objects marked by squares correspond to those in Tables 3 and 4. The open circles mark additional objects observed spectroscopically, but not included in the analysis of this paper, because of the extreme faintness or the absence of emission lines. Orientation is North to the top and East to the left.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig2.eps}\end{figure}$ Figure 2: H II region identification for NGC 1365. The gap in the FORS2 CCD mosaic runs horizontally.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig3.eps} \end{figure}$ Figure 3: H II region identification for NGC 2903.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig4.eps} \end{figure}$ Figure 4: H II region identification for NGC 2997. The gap in the FORS2 CCD mosaic runs horizontally.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig5.eps} \end{figure}$ Figure 5: H II region identification for NGC 5236.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=17cm,clip]{3369fig6.eps} \end{figure}$ Figure 6: ( Top) The combined spectrum of NGC 1232-07, showing the full extent of the spectral coverage of our observations. Two different vertical scales are used. The insets show zoomed-in portions of the spectrum, where strong stellar features are located: Balmer absorption lines and WR emission lines. ( Bottom) Portion of the spectrum observed in NGC 1365-15, with the auroral lines [N II] $~\lambda$ 5777 and [S III] $~\lambda$ 6312 highlighted.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=16cm,clip]{3369fig7.eps} \end{figure}$ Figure 7: ( Top) The blue portion of the spectrum of NGC 2903-08, a low-excitation H II region, as indicated by the weak [O III] $~\lambda\lambda$ 4959, 5007 emission. Emission features due to WR stars are seen at 4680 Å (WN subtypes), 5696 Å and 5808 Å (WC subtypes). ( Bottom) Portion of the spectrum of NGC 5236-11, a hot-spot H II region located in the nucleus of the galaxy. Several stellar (WR 4680 bump, Balmer absorption lines) and interstellar (Ca II, Na I) features are seen, together with auroral lines ([N II] $~\lambda$ 5755, [S III] $~\lambda$ 6312).
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{3369fig8.eps} \end{figure}$ Figure 8: Comparison of reddening-corrrected line intensities (in units of H $\beta$ = 100) measured in the current work (x-axis) with published values from the literature (y-axis). The four panels refer to the strong lines [O II] $~\lambda$ 3727 ( top left), [O III] $~\lambda$ 5007 ( top right), [N II] $~\lambda$ 6583 ( bottom left) and [S II] $~\lambda\lambda$ 6716,6731 ( bottom right). The five target galaxies shown are: NGC 1232 (open triangles), NGC 1365 (open circles), NGC 2903 (crosses), NGC 2997 (full circles), NGC 5236 (open squares). Different colors are used for different comparison data, which are taken from the studies mentioned in the text.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig9.eps} \end{figure}$ Figure 9: The electron density-sensitive ratio [S II] $~\lambda$ 6716/[S II] $~\lambda$ 6731 plotted against the empirical abundance indicator R₂₃ for our H II region sample. The scale on the right provides an approximate density scale (in cm^-3). The zero-density limit is indicated by the dashed line. Here and in the following diagrams we use the following symbols to differentiate nebulae in the different galaxies: NGC 1232 ( open triangles), NGC 1365 ( open circles), NGC 2903 ( crosses), NGC 2997 ( filled circles) and NGC 5236 ( open squares).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig10.eps} \end{figure}$ Figure 10: The ratio between the measured [O III] $~\lambda$ 5007 and [O III] $~\lambda$ 4959 fluxes ( top) and between the [N II] $~\lambda$ 6583 and [N II] $~\lambda$ 6548 fluxes ( bottom), compared with the theoretical expectation ([O III] $~\lambda$ 5007/[O III] $~\lambda$ 4959 = [N II] $~\lambda$ 6583/[N II] $~\lambda$ 6548 = 3), drawn as a continuous line. The dotted lines show the $\pm$ 10% deviations from the predicted value.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig11.eps} \end{figure}$ Figure 11: Nebular diagnostic diagrams showing the excitation sequence of our sample. As a function of $\log$ ([O III] $~\lambda$ 5007/H $\beta$ ) we plot $\log$ ([N II] $~\lambda$ 6583/H $\alpha$ ) ( left) and $\log$ ([S II] $~\lambda\lambda$ 6716,6731/H $\alpha$ ) ( right). The curves represent the theoretical upper boundaries calculated by Dopita et al. (2000).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig12.eps} \end{figure}$ Figure 12: The radial distribution of the extinction c(H $\beta$ ) within the target galaxies. The deprojected radial distances of the individual H II regions have been normalized to the isophotal radius R₂₅ of the parent galaxy.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig13.eps} \end{figure}$ Figure 13: Comparison of statistical abundance indicators: R₂₃ plotted against O3N2 ( top), N2 ( middle) and log S₂₃ ( bottom). The horizontal dotted lines show the index value corresponding to the solar O/H abundance [12 + log(O/H) $_\odot$ = 8.69, Allende Prieto et al. 2001], according to the calibrations of Pettini & Pagel (2004, )tex2html_wrap_inline2478#, N2# and Díaz & Pérez-Montero (2000, S₂₃). The shaded areas below or above these lines define the regions of over-solar metallicity. The vertical light-grey band represents the solar O/H value derived from the R₂₃ calibration of Pilyugin (2001), for the range of the excitation parameter (P = 0.1-0.3) which comprises the majority of the H II regions in our sample. The arrow shows the direction of increasing oxygen abundance according to the R₂₃ method.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{3369fig14.eps} \end{figure}$ Figure 14: Oxygen abundance from statistical methods: the P-method (Pilyugin 2001) against O3N2 (Pettini & Pagel 2004).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig15.eps} \end{figure}$ Figure 15: The radial oxygen abundance gradients in the 5 galaxies, estimated via the P-method of Pilyugin (2001). The deprojected radial distances of the H II regions are normalized to the isophotal radius of the parent galaxy.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig16.eps} \end{figure}$ Figure 16: The temperature T(5755) determined from the [N II] $~\lambda$ 5755/[N II] $~\lambda\lambda$ 6548,6583 ratio compared with the temperatures measured from the auroral lines [S III] $~\lambda$ 6312 ( top), [O II] $~\lambda$ 7325 ( middle) and [S II] $~\lambda$ 4072 ( bottom). In the top panel the dashed line represents the relationship predicted by the models of Garnett (1992), while in the remaining 2 panels the line shows the location in the diagrams where T(5755) = T(7325) and T(5755) = T(4072), respectively.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig17.eps} \end{figure}$ Figure 17: The S/O ( top) and N/O ( bottom) abundance ratio trends with O/H for all objects in Table 12. A comparison sample, drawn from Garnett et al. (1997, NGC 2403), Kennicutt et al. (2003, M 101) and Bresolin et al. (2004, M 51), is shown by small full square symbols. The solar values, indicated by the $\odot$ symbol, are taken from Lodders (2003).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig18.eps} \end{figure}$ Figure 18: Same as Fig. 17, but including only nebulae from the VLT sample where the electron temperature has been computed from the availability of at least one of the [N II] $~\lambda$ 5755 and [S III] $~\lambda$ 6312 auroral lines (objects marked by asterisks in Table 12). The dashed line represents a simple model, in which a primary nitrogen component is superposed on a secondary component, which is proportional to O/H.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig19.eps} \end{figure}$ Figure 19: The abundance indicator R₂₃ as a function of oxygen abundance, including all H II regions with measured [N II] $~\lambda$ 5755 or [S III] $~\lambda$ 6312 auroral lines. The comparison sample (small squares) is the same as in Fig. 17. The continuous and dotted lines show, respectively, the R₂₃ calibrations by Edmunds & Pagel (1984) (EP84) and Pilyugin (2001) (P01). The latter has been drawn for two different values of the excitation parameter, P=0.1 and P=0.3. This range encompasses the majority of the H II regions in the VLT sample.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig20.eps} \end{figure}$ Figure 20: Comparison between direct ( $T_{\rm e}$ -based) abundances and those estimated via the R₂₃ calibration of Pilyugin (2001). The dotted lines are drawn 0.15 dex below and above the line of equal value.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig21.eps} \end{figure}$ Figure A.1: The spectrum of a QSO from our MOS setup in NGC 1365.

In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig2.eps}\end{figure}$	Figure 2: H II region identification for NGC 1365. The gap in the FORS2 CCD mosaic runs horizontally.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig3.eps} \end{figure}$	Figure 3: H II region identification for NGC 2903.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig4.eps} \end{figure}$	Figure 4: H II region identification for NGC 2997. The gap in the FORS2 CCD mosaic runs horizontally.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig5.eps} \end{figure}$	Figure 5: H II region identification for NGC 5236.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig11.eps} \end{figure}$	Figure 11: Nebular diagnostic diagrams showing the excitation sequence of our sample. As a function of $\log$ ([O III] $~\lambda$ 5007/H $\beta$ ) we plot $\log$ ([N II] $~\lambda$ 6583/H $\alpha$ ) ( left) and $\log$ ([S II] $~\lambda\lambda$ 6716,6731/H $\alpha$ ) ( right). The curves represent the theoretical upper boundaries calculated by Dopita et al. (2000).
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$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig12.eps} \end{figure}$	Figure 12: The radial distribution of the extinction c(H $\beta$ ) within the target galaxies. The deprojected radial distances of the individual H II regions have been normalized to the isophotal radius R₂₅ of the parent galaxy.
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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{3369fig14.eps} \end{figure}$	Figure 14: Oxygen abundance from statistical methods: the P-method (Pilyugin 2001) against O3N2 (Pettini & Pagel 2004).
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$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig15.eps} \end{figure}$	Figure 15: The radial oxygen abundance gradients in the 5 galaxies, estimated via the P-method of Pilyugin (2001). The deprojected radial distances of the H II regions are normalized to the isophotal radius of the parent galaxy.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig17.eps} \end{figure}$	Figure 17: The S/O ( top) and N/O ( bottom) abundance ratio trends with O/H for all objects in Table 12. A comparison sample, drawn from Garnett et al. (1997, NGC 2403), Kennicutt et al. (2003, M 101) and Bresolin et al. (2004, M 51), is shown by small full square symbols. The solar values, indicated by the $\odot$ symbol, are taken from Lodders (2003).
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$\begin{figure} \par\includegraphics[width=8cm,clip]{3369fig20.eps} \end{figure}$	Figure 20: Comparison between direct ( $T_{\rm e}$ -based) abundances and those estimated via the R₂₃ calibration of Pilyugin (2001). The dotted lines are drawn 0.15 dex below and above the line of equal value.
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