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2. The sample galaxies


2.1. Observations and data reduction

The observations were obtained, as part of a long term program, during four different observing runs from 1986 to 1989 with the ESO/MPI 2.2-m telescope at La Silla, using the Cassegrain Boller & Chivens spectrograph. In May 1986 and May 1987 we used a 320 tex2html_wrap_inline1624 512 pixel RCA CCD and a dispersion of 1.77Å pixeltex2html_wrap_inline1626; the scale perpendicular to the dispersion was 1.81 arcsec tex2html_wrap_inline1628. In March 1988 and April 1989 a 640 tex2html_wrap_inline1630 1024 pixel RCA CCD was available, giving a better dispersion (0.885 Å pixeltex2html_wrap_inline1632) and an higher scale perpendicular to the dispersion (0.885 arcsec pixeltex2html_wrap_inline1634). In all the cases the interval studied was tex2html_wrap_inline1636 4900- 5700 Å\ and the slit width was set to 1.5 arcsec on the sky. The first set of data allows a velocity dispersion resolution tex2html_wrap_inline1640 km stex2html_wrap_inline1642\ while the second one has tex2html_wrap_inline1644 km stex2html_wrap_inline1646. In addition to the galaxy spectra, every observing night the spectrum of at least one giant K star of low rotational velocity, v sin i<17 km stex2html_wrap_inline1652, was recorded for use as a template of zero velocity dispersion.

Details of the selected position angles and exposure times are given in Table 1 (click here). In Cols. 1, 2 and 3 we give the observing date, the position angle and the exposure time of each spectrum. In Col. 4 we report the seeing present during each exposure. In Cols. 5 and 6 we give the systemic velocity corrected to the sun and the central velocity dispersion (averaged over the central 3 arcsec).

All the spectra obtained have been reduced by means of the ESO-IHAP procedures and then analyzed using the FQ method (Bertola et al. 1984) generating the stellar rotation and velocity dispersion curves reproduced in Figs. 1-5.

2.2. Description of the galaxies

In the following, the principal characteristics of the galaxies are summarized. The values reported for the velocity dispersion and for the systemic velocity are computed from the mean of the different spectra. Our systemic velocities are generally in agreement with the values reported by RC3. The greatest difference we found is tex2html_wrap_inline1654100 km stex2html_wrap_inline1656  for NGC 4754.

Their observed properties are listed in Table 2 (click here), for the discussion in Sect. 3 (click here).

Figure 2: Velocity dispersion (tex2html_wrap_inline1658) and Radial Velocity (V) curves for the six galaxies for which new data are presented. All the velocities are heliocentric. The continuum line is the model velocity, as explained in the text

Figure 3: As in the previous figure

Figure 4: As in the previous figure

Figure 5: Rotation curves of galaxies included in the samples, fitted with a model of circular rotation on the galaxy plane. See the text for more details

Figure 6: As in the previous figure

Figure 7: As in the previous figure

Table 2: Observed properties of sample galaxies. The systemic velocity cz and the central velocity dispersion are extracted by the detailed studies on the single galaxies cited in the text. Galaxy inclinations i are deduced assuming an intrinsic axial ratio 0.25

NGC 3271

This galaxy is classified SB0(r) in RC3 (de Vaucouleurs et al. 1991) and Sa by Sandage & Bedke (1995) (RSA). The optical image show a quite thick bar, extending tex2html_wrap_inline1698, a quite high percentage of the disk. At the ends of the bar, two dust lanes mark two incipient spiral arms (Fig. 1).

In the literature, no kinematical data are available. The bar is along tex2html_wrap_inline1700, tex2html_wrap_inline1702 from the apparent major axis of the galaxy. From our data we derive a maximum rotational velocity of tex2html_wrap_inline1704150 km stex2html_wrap_inline1706 along the major axis. The velocity dispersion has a very pronounced maximum of tex2html_wrap_inline1708250 km stex2html_wrap_inline1710 in the nucleus. This peaked trend appears in all the four position angles studied. The velocity dispersion decrease to tex2html_wrap_inline1712100 km stex2html_wrap_inline1714 in the outer regions (tex2html_wrap_inline1716) on both sides of the galaxy, where the disk dominates.

NGC 4371

This galaxy has been classified SB0(r)+ by RC3 and SB0tex2html_wrap_inline1718(r)3 by RSA. The bar is clearly visible along the apparent minor axis of the disk. It has been studied also by Kormendy (1982a) by means of a spectrum at tex2html_wrap_inline1720 (tex2html_wrap_inline1722 from major axis). He found a central velocity dispersion tex2html_wrap_inline1724 km stex2html_wrap_inline1726 and a maximum of rotation of 125 km stex2html_wrap_inline1728. From our data, taken at tex2html_wrap_inline1730, we measure a higher rotational velocity tex2html_wrap_inline1732190 km stex2html_wrap_inline1734 and also a slightly higher velocity dispersion tex2html_wrap_inline1736 km stex2html_wrap_inline1738.

NGC 4596

This is a well known example of SB0 galaxy; SB0(r)+ in RC3. It has been yet classified as SBa(very early) in RSA. Photometry and kinematics of the bar have been studied by Kent (1990), who found that the bar in this galaxy is roughly rectangular, and that the kinematics of the bar do not differ from the mean rotation of the disk of the galaxy. The rotation curve along the bar shows a peak of velocity near the center, followed by a decrease and by a new rise outward. This shape is confirmed by our measurements and it appears to be another case of the waving rotation curve phenomenon observed in the bars of many SB0s (Bettoni 1989). The velocity dispersion is almost constant along all the observed PAs and our value (Table 2 (click here)) is in very good agreement with previous published data (Mcelroy 1995).

NGC 4754

This barred S0 is classified SB0(r)- in RC3 and tex2html_wrap_inline1740(s) in RSA. The bar is not very strong and is confined in the inner regions of the bulge of the galaxy. The kinematics along the major and minor axes of the bar in this galaxy has been studied by Jarvis et al. (1988). They found a velocity gradient of 100 km stex2html_wrap_inline1742 along both axes. Our data along tex2html_wrap_inline1744 (bar major axis) are in good agreement.

NGC 6744

This extended barred spiral galaxy is classified SAB(r)bc in RC3 and Sbc(r)II/SBbc(r)II in RSA. This spiral galaxy has been included in our sample of SB0 because the region dominated by the bar is very extended and quite clean from gas. The results can be then easily compared with the more classical SB0 galaxies. The only kinematical data available for this galaxy are from HI observations (Whiteoak & Gardner 1977). The HI offsets pointing along the major axis shows the two-horned profile typical of spiral galaxies, a maximum of tex2html_wrap_inline1746 km stex2html_wrap_inline1748 is reached at 18 arcmin. Our measured stellar rotation curve, in the central 3 arcmin, is in agreement with the HI data and reaches a maximum of rotation of tex2html_wrap_inline1750 km stex2html_wrap_inline1752. No emission lines are visible in our green spectra, but Veron-Cetty & Veron (1986) report the presence of [NII] and Htex2html_wrap_inline1754.

NGC 7079

This galaxy is a member of a group (Garcia 1993) and is a member of a physical pair (# 351, Reduzzi & Rampazzo 1995), it has been classified as SB0(s)0 by RC3 and SBa by RSA. The bar in this galaxy is not very strong.

For this galaxy Bettoni & Buson (1987) indicate the presence of faint emission lines; in our spectra it has been possible to measure only the O[III] tex2html_wrap_inline1756 Å line, in the nuclear region within 15 arcsec. From our measurements we found that the gas is in counter-rotation with respect to the stars along all the four observed position angles. Probably we are observing a very small disk of gas, whose maximum extension is tex2html_wrap_inline1758 (along the apparent major axis).

2.3. Expanding the database

Together with the new data discussed in the previous paragraph, we have included in this paper the velocity curves of 8 more galaxies, observed at La Silla with the same spectrograph, within the same long term project. They are: NGC 2217 (Bettoni et al. 1990), NGC 2983 (Bettoni et al. 1988), NGC 6684 (Bettoni & Galletta 1988), NGC 4546 (Galletta 1987; Bettoni et al. 1991), NGC 4267, NGC 4643 (Magrelli et al. 1992), NGC 4684 (Bettoni et al. 1993) and NGC 4442 (Bettoni & Galletta 1994). The above galaxies have been observed with the same telescope and spectrograph (2.2 m ESO- MPI + B&C) and have the same quality of the previous data. The only exception are NGC 2983 and NGC 6684 that have been observed with the B&C spectrograph mounted at the Cassegrain focus of the 3.6 m ESO telescope. For these latter the velocity resolutions (37 km stex2html_wrap_inline1794) and the scale (1.93 arcsec/pixel) are similar. Due to particular features present in these galaxies (counter-rotation, filaments, bar asymmetries), part of their kinematical data have been already published. A description of the main photometric and kinematical properties of these galaxies has been reported in the corresponding papers. In Table 5 are reported the kinematical data for the sample galaxies. Radii are in arcsec; V and tex2html_wrap_inline1798 are in km/s. These data are plotted in Figs. 2-7.

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