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 320 512 pixel
RCA CCD and a dispersion of 1.77Å pixel
; the scale
perpendicular to the dispersion was 1.81 arcsec
. In March
1988 and April 1989 a 640
1024 pixel RCA CCD was available,
giving a better dispersion (0.885 Å pixel
) and an higher
scale perpendicular to the dispersion (0.885 arcsec pixel
). In
all the cases the interval studied was
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
km s
\
while the second one has
km s
. 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 s
, 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.
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 100 km s
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 () 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 , 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 ,
from the apparent major axis of the
galaxy. From our data we derive a maximum rotational velocity of
150 km s
along the major axis. The velocity dispersion has a
very pronounced maximum of
250 km s
in the nucleus. This peaked
trend appears in all the four position angles studied. The velocity
dispersion decrease to
100 km s
in the outer regions
(
) on both sides of the galaxy, where the disk dominates.
NGC 4371
This galaxy has been classified SB0(r)+ by RC3 and SB0(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
(
from major axis). He found a
central velocity dispersion
km s
and a maximum of rotation
of 125 km s
. From our data, taken at
, we measure a higher
rotational velocity
190 km s
and also a slightly higher
velocity dispersion
km s
.
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 (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 s
along both
axes. Our data along
(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
km s
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
km s
. No emission lines are visible in our green spectra, but
Veron-Cetty
& Veron (1986) report the presence of [NII] and H
.
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] 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
(along the apparent major axis).
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 s) 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
are in
km/s. These data are plotted in Figs. 2-7.