Astronomy & Astrophysics

All Figures

$\begin{figure} \par\includegraphics[width=6.3cm,clip]{0529_f1a.eps}\hspace*{4mm} \includegraphics[width=6.3cm,clip]{0529_f1b.eps} \end{figure}$ Figure 1: The 6 long-slits overlaid on an H $\alpha$ image of NGC 2403, taken from the archive of the Canadian French Hawaiian (CFH) Telescope (Drissen et al. 1999). The total exposure times in each position are given in Table 1.
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In the text

$\begin{figure} \par\includegraphics[width=11cm,clip]{0529_f2.eps} \end{figure}$ Figure 2: Optical spectra for NGC 2403 in the spectral range 6555-6600 Å. The upper left panel shows the original spectrum taken along the major axis of NGC 2403 in the N-W approaching side of the galaxy (slit 1 in Fig. 1), the centre of the galaxy is at the bottom. The curvature of the emission lines (H $\alpha$ and [N II]) is caused by the differential rotation. The upper right panel shows a sky exposure in the same spectral range; a spatial median filter was applied to this image. The lower panels show the same spectrum as the upper left panel after the sky subtraction. Bottom left: sky subtraction obtained using the sky exposure. Bottom right: sky subtraction with the Gaussian fit of the sky lines as described in the text. The second method gives a better result. The negative values in the bottom part of the spectra are probably caused both by stellar light absorption within NGC 2403 and uncertainties in the continuum subtraction. The contours of all these spectra are 3, 6, 12 ... in units of rms noise of the original map, 1 $\sigma = 7.96 \times 10^{-19}$ erg s^-1 cm^-2 Å^-1 pixel^-1.
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In the text

$\begin{figure} \par\includegraphics[width=6.2cm,clip]{0529_f3a.eps}\hspace*{2mm} \includegraphics[width=6.2cm,clip]{0529_f3b.eps} \end{figure}$ Figure 3: Optical H $\alpha$ rotation curve for NGC 2403. The left panel shows the rotation velocity for the receding (open squares) and approaching (filled squares) sides of the galaxy. The right panel shows the final rotation curve. In the right plot the error bars are obtained from differences between the approaching and the receding sides and the continuous line shows the H I rotation curve.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{0529_f4.eps} \end{figure}$ Figure 4: Position-velocity diagram along the major axis of NGC 2403 for H $\alpha$ ( left) and H I ( right), both at full spatial and velocity resolution: 1 $'' \times 40$ km s^-1 and 15 $'' \times 10$ km s^-1respectively. The H $\alpha$ data are obtained by combining the observations along the major axis (slit 1, 3, and 5). The H I data are taken from Fraternali et al. (2002a). The white dots show the H I rotation curve. The contour levels, respectively for H $\alpha$ and H I are -30, -9, -3, 3, 9, 30, 75, 225, 450 and -4, -2, 2, 4, 8, 16, 40, 80 in terms of rms noise.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{0529_f5.eps} \end{figure}$ Figure 5: Position-velocity diagrams along the major axis of NGC 2403 for H $\alpha$ ( left panel) and H I ( right panel) at similar spatial and velocity resolutions. The dots show the H I rotation curve. The contour levels, respectively for H $\alpha$ and H I are -12, -6, -3, 3, 6, 12, 30, 66, 120, 300, 600, 1200 and -4, -2, 2, 4, 8, 16, 32, 64 in terms of rms noise of the smoothed data. The negative levels in the central regions of the H $\alpha$ plot are due to continuum subtraction and stellar absorption in NGC 2403.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{0529_f6a.eps}\par\vspace*{2mm} \includegraphics[width=12.5cm,clip]{0529_f6b.eps} \end{figure}$ Figure 6: Composite H $\alpha$ line profiles along the major axis of NGC 2403 for both the approaching ( upper panels) and receding ( lower panels) sides of NGC 2403. The continuous line indicates the Gaussian fit. The tails are visible at low rotation velocities (negative velocities in these plots). Right panels show the residuals.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{0529_f7a.eps}\par\vspace*{2mm} \includegraphics[width=12.5cm,clip]{0529_f7b.eps} \end{figure}$ Figure 7: Composite [N II] line profiles along the major axis of NGC 2403 for both the approaching ( upper panel) and receding ( lower panel) sides of NGC 2403. The continuous line indicates the Gaussian fit. The tails are visible at lower rotation velocities (negative velocities in these plots). Right panels show the residuals.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0529_f8.eps} \end{figure}$ Figure 8: [N II]/H $\alpha$ intensity ratio versus velocity difference from the rotation of the disk. The ratio is normalized at zero velocity. The line ratio shows an increase at decreasing rotation velocities as expected if this gas is located above the plane of the disk.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{0529_f9a.eps}\par\vspace*{2mm} \includegraphics[width=12.5cm,clip]{0529_f9b.eps} \end{figure}$ Figure 9: Composite line profiles for H $\alpha$ along the minor axis of NGC 2403 in the S-W and N-E sides of the galaxy ( left panels). The continuous line indicates the Gaussian fit. The right panels show the residuals. Velocities are with respect to systemic. The tail at high velocity in the S-W (near) side and at low velocity in the N-E (far) side may indicate a large-scale radial inflow.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{0529_f10.eps} \end{figure}$ Figure 10: Left panel: optical spectrum along the major axis of NGC 2403 (slit 5 in Fig. 1) in the spectral range of H $\alpha$ and [N II]. Note the large velocity dispersion of features visible in the receding (S-E) side of the galaxy (bottom of this image). Right panels: H $\alpha$ line profiles through the broad features 1 and 2 observed along the major axis of NGC 2403 and shown in the left panel. The velocities are heliocentric.
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In the text

$\begin{figure} \par\includegraphics[width=6.3cm,clip]{0529_f1a.eps}\hspace*{4mm} \includegraphics[width=6.3cm,clip]{0529_f1b.eps} \end{figure}$	Figure 1: The 6 long-slits overlaid on an H $\alpha$ image of NGC 2403, taken from the archive of the Canadian French Hawaiian (CFH) Telescope (Drissen et al. 1999). The total exposure times in each position are given in Table 1.
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$\begin{figure} \par\includegraphics[width=12.5cm,clip]{0529_f6a.eps}\par\vspace*{2mm} \includegraphics[width=12.5cm,clip]{0529_f6b.eps} \end{figure}$	Figure 6: Composite H $\alpha$ line profiles along the major axis of NGC 2403 for both the approaching ( upper panels) and receding ( lower panels) sides of NGC 2403. The continuous line indicates the Gaussian fit. The tails are visible at low rotation velocities (negative velocities in these plots). Right panels show the residuals.
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$\begin{figure} \par\includegraphics[width=12.5cm,clip]{0529_f7a.eps}\par\vspace*{2mm} \includegraphics[width=12.5cm,clip]{0529_f7b.eps} \end{figure}$	Figure 7: Composite [N II] line profiles along the major axis of NGC 2403 for both the approaching ( upper panel) and receding ( lower panel) sides of NGC 2403. The continuous line indicates the Gaussian fit. The tails are visible at lower rotation velocities (negative velocities in these plots). Right panels show the residuals.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0529_f8.eps} \end{figure}$	Figure 8: [N II]/H $\alpha$ intensity ratio versus velocity difference from the rotation of the disk. The ratio is normalized at zero velocity. The line ratio shows an increase at decreasing rotation velocities as expected if this gas is located above the plane of the disk.
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