3 Comparisons and individual results

The reliability of our reduction procedure was examined comparing our measurements with those derived by other authors. Comparisons with the literature are quite difficult both for the systemic velocity and for the central velocity dispersion. In particular, an accurate comparison with the central velocity dispersions from the literature is hard to achieve, given the wide range in effective spatial resolution, the overall quality of the data, the diverse techniques and instrumentations used in different studies.

The check of the systemic velocity determination is done mainly using the heliocentric optical, $V_{\rm opt}$, velocity value listed in RC3 (de Vaucouleurs et al. 1991) and that listed in Reduzzi & Rampazzo (1995: hereafter RR95), since these sources offer the largest intersection and homogeneity with our sample. RR95 atlas reports systemic velocities derived from ESO-LV (Lauberts & Valentijn 1989) up to dated with measures obtained from recent surveys (Fairall & Jones 1991; da Costa, private communication). A compilation of velocity dispersion measurements has been recently published by Prugniel & Simien (1996: PS96 hereafter). PS96 is then our source for the comparison between our measurements of the central velocity dispersions an those available in the literature.

  

Figure 1: (bottom panel) Comparison between our heliocentric systemic velocities and $V_{\rm opt}$ reported in RC3 for 26 common galaxies. (medium panel) The systemic velocity of pair members has been compared with literature data reported in RR95 catalogue. In both panels are plotted the average residual and the relative $1 \sigma$uncertainty. (upper panel) Systemic velocity distribution of pair members and shell galaxies

Figure 1 shows the difference between our heliocentric systemic velocities and the corresponding values reported in RC3. Among 26 of the 29 galaxies in common, the mean difference (our - RC3) is $-1\pm 32$km s^-1. In three cases there is a quite large difference between our measurements and $V_{\rm opt}$ from RC3, namely for NGC 7135, NGC 7284 and IC 5250. The heliocentric systemic velocity quoted in RC3 for NGC 7135 is 2050$\pm$35 km s^-1. Our value (Table 2) substantially agrees with 2718$\pm$30 km s^-1 given in Tully (1988). NGC 7284 according to RC3 has a systemic velocity of $4544\pm 65$ km s^-1. Our value is in good agreement with the value 4706 km s^-1 reported in ESO-LV. Analogously, RC3 reports for IC 5250 a systemic velocity of $3509\pm 37$ km s^-1 while ESO-LV and and Fairall & Jones (1991) report respectively 2947 and 3123 km s^-1, in agreement with our determination. A mean difference of $8\pm$ 38 km s^-1 is found comparing our systemic velocities for 21 pair members and data from RR95. The scatter with data from RC3 and from RR95 are probably due to the fact that part of the systemic velocity measurements comes from surveys which offer a lower precision than that obtained in detailed kinematic investigations. If we compare our systemic velocities to those obtained by Carter et al. (1988), a study dedicated to shell galaxies, we obtain a mean difference of $-18\pm 15$km s^-1 over 10 out of 11 common galaxies; only one object, namely E5390100, has a difference of 107 km s^-1 with our estimate.

  

Figure 2: Comparison between our values of nuclear velocity dispersion $\sigma_{5\hbox{$^{\prime\prime}$}}$ and those obtained by Gonzalez (1993: bottom panel), Carter et al. (1988: medium panel) and 7Sam (upper panel). In this latter panel our nuclear velocity dispersion for NGC 7785 and NGC 7619, the two upper points, disagree with the correspondent values adopted by 7Sam. These galaxies belong also to the set of G93 with which the agreement is quite good

In Fig. 2, values of $\sigma_{\rm 5''}$ are compared with the two sets of data coming from G93 and Davies et al. (1987: 7Sam). Gonzalez's nuclear ($\sigma_{5''}$) velocity dispersions of the five galaxies in Table 1 compare within $9\pm 9$ km s^-1 with our measurements. G93 states that his nuclear velocity dispersions show a small positive offset when compared with 7Sam and Whitmore et al. (1985) data. At the same time, the average (our - 7Sam) difference of nuclear velocity dispersion is $10\pm 27$km s^-1 among 12 common objects. Values of the central velocity dispersions, $\sigma_0$, are compared in the same figure with those obtained by Carter et al. (1988). The average difference (our - Carter et al.) is $2\pm 33$ km s^-1. With respect to these authors, our kinematic zero point is then systematically positive by a very small factor, which anyway cannot affect the quality of the velocity dispersion correction applied to spectro-photometric data.

Velocity, $V_{\rm hel}$, and velocity dispersion, $\sigma$, curves as function of the distance from the centre are displayed in Figs. 3, and 4. In particular, Fig. 3 displays the comparisons with other authors for the 5 galaxies from the Gonzalez's (1993) set considered in Paper I as spectro-photometric templates. Detailed comparisons are discussed in the next subsections.

  

Figure 3: Rotation (left panel) and velocity dispersion curves (right panel) as a function of the distance from the centre for the set of galaxies used as spectro-photometric templates. Comparisons between our measurements (full dots) and the data available in the literature are also shown. NGC 584: Davies & Illingworth (1983: open squares); NGC 7562, NGC 7619: Whitmore et al. (1987: asterisks), Jedrzejewski & Schechter (1989: open squares), Franx et al. (1989: open pentagons); NGC 7626: Jedrzejewski & Schechter (1989: open squares), Davies & Birkinshaw (1988: asterisks); NGC 7785: Bender et al. (1994: open squares)

 

Table 1: Main kinematic data

 

Table 1: continued

3.1 Individual notes and comparison with the literature for the galaxies in the G93 sample

NGC 584: Figure 3 shows the good agreement between our rotation and velocity dispersion profiles and those obtained by Davies & Illingworth (1983) along PA 63$^{\circ}$. 7Sam adopted a central velocity dispersion of 217 km s^-1 (raw data range between 215 and 245 km s^-1) in good agreement with our data reported in Table 1.

NGC 7562: Although in agreement within the errors, our value of the central velocity dispersion is $\approx$20 km s^-1 higher than those obtained from Gonzalez (1993: 244 km s^-1) and 7 Sam (243 km s^-1).

NGC 7619: Figure 3 shows the comparison with Whitmore et al. (1987), Jedrzejewski & Schechter (1987) (PA = 34$^{\circ}$) and Franx et al. (1989). Our data agree, within the errors, with both Jedrzejewski & Schechter (1989) and Franx et al. (1989). A zero point difference is evident, both in systemic velocity and velocity dispersion, with Whitmore et al. (1987) data. On the other side, the shape of their velocity profile is more similar to our one than that of Jedrzejewski & Schechter (1987) and Franx et al. (1989). Our central velocity dispersion is in agreement with that derived by 7Sam since their adopted value is 337 km s^-1 (raw values range from 325 to 381 km s^-1).

NGC 7626: While our velocity curve is in agreement with that from both Jedrzejewski & Schechter (1989) (PA = 7) and Davies & Birkinshaw (1988) ($\rm PA = 4^\circ$), our velocity dispersion profile presents a small positive zero point shift with respect to that obtained by the latter authors. The central velocity dispersion adopted by 7Sam is 234 km s^-1 (raw data range from 208 to 275 km s^-1). The average value in the literature (PS96) is $\sigma_0$=268 km s^-1, well in agreement with our estimate.

NGC 7785: Bender et al. (1994) have obtained for this galaxy rotation and velocity dispersion profiles along a $\rm PA= 138^\circ$.Figure 3, in which the comparison with our measurements is shown, indicates a good agreement between the two sets of data. 7Sam adopted value of the central velocity dispersion, 291 km s^-1 (raw value 299 km s^-1), is the highest in the literature.

  Table 2: Futher information on pairs

3.2 Individual notes and comparison with the literature for shells galaxies

In the Figs. 4.1-4, the velocity and velocity dispersion curves of the shell galaxies are presented. Note that the shell galaxy IC 1609 is not part of the spectrophotometric sample analyzed in Paper I.

NGC 1316: Schweizer (1981) studied the optical properties of the NGC 1316 core obtaining an estimate of the central velocity dispersion of 248$\pm$6 km s^-1. Both this value and the average one in the literature (250 km s^-1, PS96) are in agreement with our measure.

NGC 1549: This galaxy is interacting with NGC 1553 (Malin & Carter 1983). The galaxy geometry is characterized by a strong twisting (Rampazzo 1987) and shows significant rotation along different axes (Rampazzo 1988; Franx et al. 1989). PS96 report 213 km s^-1 as the average value in the literature for central velocity dispersion, in good agreement with our nuclear value.

NGC 1553: Differently from the companion NGC 1549, the geometry of NGC 1553 is characterized by a nearly constant position angle. The extended velocity curves studied by Kormendy (1984) and Rampazzo (1988), along $\rm PA = 149\hbox{$.\!\!^\circ$}5$ and $\rm PA = 140^\circ$ respectively, show a secondary maximum ($\approx$ at 10$^{\prime\prime}$), visible also in our velocity curve. No rotation is measured by the previous authors along the minor axis ($\rm PA = 59\hbox{$.\!\!^\circ$}5$; $\rm PA = 50^\circ$ axes respectively) confirming that NGC 1553 is a lenticular galaxy. PS96 report 185 km s^-1 as the average value in the literature for the central velocity dispersion, in good agreement with our nuclear value.

NGC 2865: Bettoni (1992) has obtained the velocity curve (PA = 150) and the central velocity dispersion for this galaxy. The velocity profile obtained by the previous author is in good agreement with our measurement. This galaxy shows a large external complex of HI (Schiminovich et al. 1995) with a systemic velocity of 2640$\pm$15 km s^-1 well in agreement with our determination for the stellar component. Stars and gas seem then to be associated and co-rotating, as outlined by the previous authors. Our value of the central velocity dispersion is in agreement with the Carter et al. (1988) value of 208$\pm$46 km s^-1. Lower values, although in agreement within the errors, are given by Bettoni (1992) 180$\pm$24 and 7Sam whose adopted value is 168 km s^-1 (raw data range from 161 to 199 km s^-1).

NGC 5018: The galaxy has been recently observed by Carollo & Danziger (1993) along both the major (PA $99^\circ$)and minor (PA $9^\circ$) axis. Our rotation and velocity dispersion curves agree with their ones. In particular the velocity dispersion curve shows a deep of $\approx$ 50 km s^-1 slightly displaced (1$.\!\!^{\prime\prime}$8) from the centre. Carollo & Danziger (1993) model the dynamics of NGC 5018 suggesting that velocity and velocity dispersion curves are well fitted by an oblate rotator, with a flat diffuse dark halo 3 times as large as the luminous component.

NGC 6849: The galaxy shows a regular rotation ($\approx$75 km s^-1) along the major axis. The velocity dispersion curve is flat. The $\sigma$ average value in the literature (PS96) is 211 km s^-1 in agreement with our measures.

E 2890150: Stellar and gaseous components (the latter studied through the H$\beta$ emission) co-rotate, and their systemic velocities are in agreement within the errors, which for the stellar component are quite large. The average gas velocity dispersion is 82$\pm$59 km s^-1.

E 2400100: Our spectra (three independent observations) show two distinct components whose centres are indicated in Fig. 4.4 as a and b. The two components are separated by $\approx$ 5$^{\prime\prime}$ and 200 km s^-1 in the redshift space. In the previous papers (Malin & Carter 1983; Carter et al. 1988) dealing with this object, this characteristic has not been noticed. While it is not surprising in the case of the Malin & Carter catalog, since it is obtained from very deep Schmidt plates, the fact that Carter et al. (1988) did not notice a double nucleus could be explained by a different slit PA In fact, our measure of the nuclear systemic velocity and of the velocity dispersion on the main body of the galaxy are in good agreement with those derived by Carter et al. (1988).

3.3 Individual notes and comparison with the literature for pairs members

Reduzzi & Rampazzo (1996: R&R96 hereafter) have obtained the B, V, R surface photometry of most of the present sample pairs. In R&R96 Table 4, informations about the galaxies inner fine structure and possible morphological misclassification on the basis of luminosity, geometric and color profiles are also given. The Figs. 4.5-4.10 report the velocity and velocity dispersion curves for this part of the sample. Note that ESO 4860290 (RR 105a) data are not riported in Fig. 4 because we obtained only the central kinematic for this object whose observations are characterized by a low S/N ratio. For completeness we have included ESO 5330320 (RR 381b), although it is not part of the spectrophotometric sample analyzed in Paper I.

ESO 2440120/121 (RR 24): Both the galaxies have a very distorted morphology (R&R96), showing long, asymmetric tails/arms. ESO 2440120/2440121 are classified as a spiral and a late S0. The (B-V) color map is consistent with the late-type classification. In the present sample they represent the objects with the latest morphological type and nuclear indices refer to their bulges. The gas velocity curve of ESO 2440120 (RR 24a) is consistent with that of the stars, while in ESO 2440121 (RR 24b), although having the same slope, the two components differ in the systemic velocity. Velocity dispersion is very small at the limit of our resolution.

ESO 5450400 (RR 62a): ESO-LV classification of this galaxy reports it as an S0 object, but the luminosity profile is well fitted by a r^1/4 law (R&R96). (B-V) color profile is consistent with an early-type galaxy.

NGC 4105/4106 (RR 210): Pair members are strongly interacting. This is visible both in the velocity and in the velocity dispersion curve of NGC 4105 (RR 210a) obtained at PA 118, i.e. along the line connecting the two nuclei. The velocity curve of RR 210a could be interpreted in the framework of U-shape profiles. The axis along which NGC 4106 (RR 210b) has been observed is less contaminated by the interaction and shows a nearly normal rotation and velocity dispersion profile. NGC 4106 is a fast rotator: the peak velocity up to the last observed point is 116 km s^-1.

ESO 3860040 (RR 278a): This galaxy is a lenticular. R&R96 found shells and dust in this galaxy. Measurements, done on independent parts of the spectrum, suggests that gas has a steeper rotation curve than stars, although in the same sense. This could be interpreted within the framework in which the stellar and gaseous components lie in different planes as already reported in other remarkable cases (Galletta 1996; Plana & Boulesteix 1996). In the central 2$.\!\!^{\prime\prime}$4 the velocity dispersion of the gas is 171 km s^-1 similar to the stellar one. It is quite difficult, without further studies, to understand the origin of the gas, which could e.g. has been accreted from the spiral companion or, having lost angular momentum during the interaction, to be conveyed from the galaxy outskirts to the centre.

 

Table 3: Definitions of the emission lines bandpasses

 

Table 4: Emission lines EW

  

Figure 4: 1. Rotation (left panel) and velocity dispersion curves (right panel) as a function of the distance from the galaxies centre for the shell objects sample. Full circles mark the stellar component. Open symbols indicate the gaseous component as determined by H$\beta$ 4861 Å line (squares), [O III] 4959 Å line (triangles) and [O III] 5007  Å line (pentagons)

 

Figure 4: 2. See Fig. 4.1

 

Figure 4: 3. See Fig. 4.1

 

Figure 4: 4. See Fig. 4.1

 

Figure 4: 5. Rotation (left panel) and velocity dispersion curves (right panel) as a function of the distance from the galaxies centre for the pair sample. Symbols are the same as in Fig. 4.1

 

Figure 4: 6. See Fig. 4.5

 

Figure 4: 7. See Fig. 4.5

 

Figure 4: 8. See Fig. 4.5

 

Figure 4: 9. See Fig. 4.5

 

Figure 4: 10. See Fig. 4.5