All Figures

$\begin{figure} \par\includegraphics[width=8cm]{0394fig1.eps}\end{figure}$ Figure 1: Large-scale kinematics of the eastern tidal tail of IC 1182. Top: optical R-band map (Iglesias-Páramo et al. 2003) and HI contours (Dickey 1997). The TDG candidate ce-61 is identified. The dashed lines delineate the band along which the PV diagram has been derived; north is to the top. Bottom: PV diagram of the tidal tail ( $20~{\rm kpc}= 28''$ ). The dashed line is an eye fit of the H $\alpha$ emission distribution along the tail. In addition to this large-scale kinematical signature, each HII region may present an inner velocity gradient.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig2.eps}\end{figure}$ Figure 2: Small-scale kinematics of a TDG candidate in the northern part of NGC 5291. Top: optical V-band map (Duc & Mirabel 1998) and HI contours (Malphrus et al. 1997); north is to the left. The dashed line indicates the slit used for the PV diagram. Bottom: PV diagram of the TDG candidate (3 kpc = 10''), showing an inner velocity gradient as large as 100 km s^-1 over 2.4 kpc.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig3.eps}\end{figure}$ Figure 3: Example of a restricted three-body simulation of two interacting galaxies, with a mass ratio of 1:1 (impact parameter 100 kpc, relative velocity 150 km s^-1, inclination 30 degrees). In the plot of the projected mass distribution ( bottom), the tidal tail is seen rather close to edge-on (inlination of 65 degrees) whereas the simulated PV diagram ( top) corresponds to the tail which would be observed exactly edge-on. A projection effect exists when part of the tail is aligned with the line-of-sight (encircled region). The velocity gradient is first positive from the parent galaxy to the outer parts, and then becomes negative before the region affected by the projection problem. This early change in the sign of the velocity gradient is the clear signature of a projection effect at the apparent tip of the tail. Further away, the observed (projected) velocity keeps on decreasing, drawing a loop in the PV diagram.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig4.eps}\end{figure}$ Figure 4: Example of a full N-body simulation of two interacting galaxies, with a mass ratio of 1:1 (impact parameter 100 kpc, relative velocity 200 km s^-1, inclination 0 degrees). In the plot of the mass distribution ( bottom), the tidal tail is seen face-on whereas the simulated PV diagram ( top) corresponds to the tail which would be observed exactly edge-on. A part of the tail is aligned with the line-of-sight (indicated with the arrow), so that a projection effect exists. In the configuration of this run, the velocity gradient is first positive and then becomes negative before the extremity of the tail.
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In the text

$\begin{figure} \par\includegraphics[width=8.7cm]{0394fig5.eps}\end{figure}$ Figure 5: PV diagrams expected for tidal tails that are seen edge-on, according to the results of our numerical simulations. Case a): no part of the tail is aligned with the line-of-sight and an observed mass concentration cannot result from a projection effect. The sign of the projected velocity gradient does not change. Case b): a projection effect exists and could be responsible for the observation of a mass concentration. The sign of the velocity gradient changes before the apparent extremity of the tail. A loop-shaped diagram is obtained when the tidal tails extends much further than the projection effect (dashed lines). The whole loop may however be difficult to detect since the most external parts of tidal tails are likely to be faint.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig6.eps}\end{figure}$ Figure 6: PV diagram of the northern tidal tail of Arp 105, from HI data of Duc et al. (1997) (20 kpc = 33''). We find here the kinematical signature expected for a tidal tail with a projection effect (case b) in Fig. 5). The band along which the PV diagram has been integrated is shown in the optical map. The crosses on the diagram and the optical map identify the position of the center of the parent spiral galaxy.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig7.eps}\end{figure}$ Figure 7: Kinematics of the southern tail of Arp 105 (NGC 3561, The Guitar). Center: optical V-band map (Duc & Mirabel 1994) and HI contours (Duc et al. 1997). North is to the right. The TDG candidate is the most luminous feature on the left of the elliptical galaxy. Top: H $\alpha$ PV diagram, and identification of a HII region hidden by the elliptical but kinematically decoupled from it (circled region); the velocity of this region coincides with the kinematics of the tidal tail issued from the spiral, so that this region is likely to belong to the tail passing in front of the elliptical. Bottom: large-scale H $\alpha$ PV diagram of thetidal tail (10 kpc = 16''). The circle indicates the mass center of the HII region identified in front of the elliptical galaxy (top image).The grey contours corresponds to the kinematics of the HI component, according to the B-array VLA observations of Brinks et al. (2004). The large-scale kinematics of this tail indicates that the TDG candidate does not result of a projection effect, but is a genuine accumulation of matter.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig8.eps}\end{figure}$ Figure 8: Kinematics of the northern tail of Arp 242. Top: DSS blue image and HI contours (Hibbard & van Gorkom 1996). North is to the left; the arrow identifies the TDG candidate. Bottom: H $\alpha$ PV diagram of the northern tail (5 kpc = 11''). The arrow indicates the H $\alpha$ peak of the TDG candidate. One could attempt to interpret the kinematics of the tail with a change in the sign of the velocity gradient and a projection effect associated with the TDG candidate (long-dashed line), but the last 5 kpc of the tail are not fitted, which rules out this interpretation. On the contrary, a more robust interpretation of the kinematics is obtained without any change in the sign of the velocity gradient, and only one HII region that is not perfectly fitted (short-dashed line), suggesting that the mass concentration in this tail is not the result of a projection effect.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig9.eps}\end{figure}$ Figure 9: Isovelocities diagram of NGC 5291 northern TDG (1 kpc = 3''). The classical spider shape, corresponding to the rotation of the system, can be identified, but is largely disturbed which probes that supplementary motions or distortions play a role.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig10.eps}\end{figure}$ Figure 10: Projected velocity of the northern TDG of NGC 5291, as a function of the position along the axis shown in Fig. 9 (1 kpc = 3''). The center of rotation is here defined as the mass center of the H $\alpha$ emission, which is very close to the H $\alpha$ emission peak. The right part of this curve, corresponding to the southern part of the TDG, is similar to the classical rotation curves of disk galaxies while the left (northern) part seems very disturbed.
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In the text

$\begin{figure} \par\includegraphics[width=7.3cm]{0394fig11a.eps}\par\includegraphics[width=4cm]{0394fig11b.eps}\end{figure}$ Figure A.1: Top: H $\alpha$ emission map of IC 1182. A DSS blue image of the same field is shown in the corner. HI contours (Dickey 1997) are superimposed in green. Bottom: PV diagram along the slit shown in the map (5 kpc = 7''). North-East is to the left of the position axis. The asymmetric aspect of this diagram suggests the presence of an internal velocity gradient that is not fully resolved, its amplitude but could be as large as 70 km s^-1. The orientation of the slit corresponds to the largest velocity gradient.

In the text

$\begin{figure} \par\includegraphics[width=6cm]{0394fig12a.eps}\par\includegraphics[width=3cm]{0394fig12b.eps}\par\end{figure}$ Figure A.2: Top: H $\alpha$ emission map of Arp 105. A DSS blue image of the same field is shown in the corner, and HI contours are superimposed (Duc & Mirabel 1998). Three main objects can be identified, from north to south: the spiral galaxy, the elliptical one, and the TDG candidate. Bottom: PV diagram of the southern TDG along the slit shown in the map (5 kpc = 8''). South-East is to the left of the position axis. The asymmetric aspect of this diagram suggests the presence of an inner velocity gradient, that is not resolved but may reach 100 km s^-1 over 2 to 3 kpc. The orientation of the slit corresponds to the largest velocity gradient.

In the text

$\begin{figure} \par\includegraphics[width=6cm]{0394fig13.eps}\end{figure}$ Figure A.3: H $\alpha$ emission map of Arp 242 with HI contours superimposed in green (Hibbard & van Gorkom 1996). A DSS blue image of the whole system is shown in the corner. The two straight lines indicate the band along which the PV diagram of the northern tail shown in Fig. 8 has been established.

In the text

$\begin{figure} \par\includegraphics[width=12cm]{0394fig14.eps}\end{figure}$ Figure A.4: Left: H $\alpha$ emission map of the northern region of NGC 5291 with HI contours superimposed in green (Malphrus et al. 1997). A DSS blue image of the system is shown in the corner. The "seashell'' galaxy is seen at its bottom. The line indicates the slit along which the velocity curve of the TDG candidate (Fig. 2) has been derived. Right: H $\alpha$ velocity field associated with the same region. Velocities indicated in the colorbar are in km s^-1.

In the text

$\begin{figure} \par\includegraphics[width=6cm]{0394fig15a.eps}\par\includegraphi... ...=6cm]{0394fig15b.eps}\par\includegraphics[width=6cm]{0394fig15c.eps}\end{figure}$ Figure A.5: Top: H $\alpha$ emission map of the central region of NGC 5291 with HI contours superimposed in green (Malphrus et al. 1997). A DSS blue image of the system is shown in the corner. Center: PV diagram corresponding to the band a) on the map above (2 kpc = 6.5''). North is to the left of the position axis. Note a dedoubling of the kinematical features around the brightest HII region, in the central regions of the parent galaxy. Duc & Mirabel (1998) had found evidences of counter-rotation is this region. Bottom: PV diagram corresponding to band b). East is to the left of the position axis; the dashed line indicates the mean velocity of most HII regions. However, the brightest HII region is largely decoupled from this mean trend.

In the text

$\begin{figure} \par\includegraphics[width=12cm]{0394fig16.eps}\end{figure}$ Figure A.6: Top: H $\alpha$ emission map of the southern region of NGC 5291 with HI contours superimposed in green (Malphrus et al. 1997). A DSS blue image of the system is shown in the corner. Bottom: PV diagram of one of the TDG candidates along the slit shown in the map (East is to the left; 2 kpc = 6.5''). Right: H $\alpha$ velocity field associated with the same region. Velocities indicated in the colorbar are in km s^-1.

In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig17.eps}\end{figure}$ Figure A.7: H $\alpha$ emission map of a northern region of Arp 243 with HI contours superimposed in green (Hibbard & Yun 1996). A DSS blue image of the same field is shown in the corner. The giant HII region associated with the western tail has been circled. The H $\alpha$ velocity field of the northern tail is shown below.

In the text

$\begin{figure} \includegraphics[width=8cm]{0394fig18.eps}\end{figure}$ Figure A.8: H $\alpha$ emission map of a northern region of Arp 244 with HI contours superimposed in green (Hibbard et al. 2001). A DSS red image of the system is shown in the corner, and the field of the H $\alpha$ map delimited by the red rectangle. We have circled HII regions associated with an H $\alpha$ line visible in the data cube, to distinguish these regions from noise (not associated with a typical emission line) and artefacts due to stars in the Fabry-Pérot interferometer.

In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig19.eps}\end{figure}$ Figure A.9: H $\alpha$ emission map of a northern region of Arp 215 with HI contours superimposed in green (Smith 1994). A DSS blue image of this object is shown in the corner. The HII region associated with the HI plume is circled.

In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig20.eps}\end{figure}$ Figure A.10: H $\alpha$ emission map of a northern region of Arp 245 with HI contours superimposed in green (Duc et al. 2000). A DSS blue image of this object is shown in the inset, and the field of the H $\alpha$ map is delimited by the red rectangle.

In the text

$\begin{figure} \par\includegraphics[width=8cm]{0394fig2.eps}\end{figure}$	Figure 2: Small-scale kinematics of a TDG candidate in the northern part of NGC 5291. Top: optical V-band map (Duc & Mirabel 1998) and HI contours (Malphrus et al. 1997); north is to the left. The dashed line indicates the slit used for the PV diagram. Bottom: PV diagram of the TDG candidate (3 kpc = 10''), showing an inner velocity gradient as large as 100 km s^-1 over 2.4 kpc.
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$\begin{figure} \par\includegraphics[width=8cm]{0394fig9.eps}\end{figure}$	Figure 9: Isovelocities diagram of NGC 5291 northern TDG (1 kpc = 3''). The classical spider shape, corresponding to the rotation of the system, can be identified, but is largely disturbed which probes that supplementary motions or distortions play a role.
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