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Astron. Astrophys. 364, 479--490 (2000) ASTRONOMY
AND
ASTROPHYSICS
Decoupled nuclei and nuclear polar rings in regular spiral galaxies
NGC 7217 #
O.K. Sil'chenko 1,##,### and V.L. Afanasiev 2,+
1 Sternberg Astronomical Institute, University av. 13, Moscow 119899, Russia
2 Special Astrophysical Observatory, Nizhnij Arkhyz, 357147 Russia
Received 21 July 2000 / Accepted 26 September 2000
Abstract. The regular isolated Sab galaxy NGC 7217 has been
studied with the Multi­Pupil Fiber Spectrograph of the 6m tele­
scope of the Special Astrophysical Observatory RAS (Nizhnij
Arkhyz, Russia) in two spectral ranges, the blue one including
the strong absorption lines Mg I and Fe I and the red one in­
cluding the emission lines H# and [N II]#6583. We confirm
the existence of a circumnuclear gaseous polar disk with a ra­
dius of 3 ## which we reported earlier. The same area, with a
radius of 3 ## --4 ## , elongated orthogonally to the line of nodes, is
distinguished by high values of the Lick index #Fe# and shows a
Mg/Fe ratio lower than solar. This implies that there were at least
two discrete star formation bursts in the circumnuclear region
with a temporal separation of a few Gyrs. We relate this pair of
bursts to the complex structure of the global brightness profile
of the galaxy, which may be decomposed into three exponential
segments with different scalelengths.
Key words: galaxies: kinematics and dynamics -- galaxies:
structure -- galaxies: spiral -- galaxies: evolution -- galaxies: nu­
clei -- galaxies: photometry -- galaxies: individual: NGC 7217
1. Introduction
A careful investigation of the inner parts in normal spiral galax­
ies with modern techniques reveals almost always a compli­
cated structure which cannot be described by a classical two­
component model consisting of a centrally concentrated, old,
red, smooth de Vaucouleurs' bulge and a more extended, young,
blue exponential disk with spiral arms. Among recent find­
ings which may have serious implications for a global evolu­
tionary picture we can mention papers on exponential bulges
Send offprint requests to: O.K. Sil'chenko (olga@sai.msu.su)
# Partly based on observations collected with the 6m telescope of the
Special Astrophysical Observatory (SAO) of the Russian Academy
of Sciences (RAS) which is operated under the financial support of
Science Department of Russia (registration number 01­43) and on data
from the ING Archive and the HST Archive.
## Isaac Newton Institute of Chile, Moscow Branch
### UK Astronomy Data Centre, Guest Investigator
+ Isaac Newton Institute of Chile, SAO Branch
Table 1. Global parameters of NGC 7217
Hubble type (R)SA(r)ab
R25 9.3 kpc
B 0
T 10.53
MB --20.5
(B - V ) 0
T 0.77
(U -B) 0
T 0.25
Vr 952 km · s -1
Distance 16.4 Mpc (H0=75 km · s -1 · Mpc -1 )
i(phot) 35 o
PA(phot) 95 o
(Andredakis et al. 1995, Courteau et al. 1996), multi­tier disks
-- e.g. in NGC 5533 (Sil'chenko et al. 1997a) or in NGC 157
(Ryder et al. 1998), decoupled circumnuclear stellar disks (e.g.
in NGC 4594, Emsellem et al. 1996), inner polar gaseous disks
(e.g. in NGC 2841, Sil'chenko et al. 1997b), circumnuclear spi­
ral arms (e.g. in NGC 5248, Laine et al. 1999, or in NGC 488,
Sil'chenko 1999), etc. In some early­type spiral galaxies, e.g.
in NGC 4138 (Jore et al. 1996) and in NGC 7217 (Merrifield
& Kuijken 1994), the existence of counterrotating stars in their
global disks was claimed. This may mean that discrete catas­
trophic events, such as minor mergers or gas accretion from a
satellite, govern the evolution of even quite regular galaxies.
But there may also exist some intrinsic evolutionary processes,
such as bar formation and dissolution due to disk instabilities or
mass concentration in the center, that can provide the same set
of properties without any external action. We cannot yet prove
either of these hypotheses because of the lack of detailed inves­
tigations of even nearby galaxies. So any new, careful analysis
of the dynamics, structure, and stellar populations in normal
spiral galaxies gives an additional chance to understand their
evolution.
Here, we present a detailed study of the regular isolated
Sab galaxy NGC 7217, the global parameters of which are
given in Table 1. The galaxy has a prominent bulge and a
truly flocculent spiral structure: unlike some other flocculent
galaxies, e.g. NGC 2841 (Block et al. 1996) or NGC 5055
(Thornley & Mundy 1997) which unveil grand design in the
NIR K­band, NGC 7217 preserves its non­wave appearance

480 O.K. Sil'chenko & V.L. Afanasiev: Decoupled nuclei and nuclear polar rings in regular spiral galaxies
Table 2. Spectral observations of NGC 7217
Date Telescope Configuration Exposure Scale Spectral range Dispersion PA(top)
19.08.98 6m BTA MPFS+CCD 1024 â 1024 60 min 1. ## 0 per lens 4250--5600 š
A 1.3 š
A /px 215 #
19.08.98 6m BTA MPFS+CCD 1024 â 1024 60 min 1. ## 0 per lens 5650--7000 š
A 1.3 š
A /px 215 #
06.01.91 4.2m WHT ISIS+CCD 800 â 1180 25 min 0. ## 335 per px 8000--8840 š
A 0.74 š
A /px 240 #
07.01.91 4.2m WHT ISIS+CCD 800 â 1180 20 min 0. ## 335 per px 5830--6680 š
A 0.74 š
A /px 150 #
07.01.91 4.2m WHT ISIS+CCD 800 â 1180 20 min 0. ## 335 per px 5830--6680 š
A 0.74 š
A /px 240 #
06.11.97 4.2m WHT ISIS+CCD 1024 â 1024 33 min 0. ## 335 per px 6150--7000 š
A 0.8 š
A /px 68 #
even at 2 µm (Elmegreen et al. 1999). But it has another puz­
zling morphological feature, namely, three stellar rings at radii
of 12 ## , 32 ## , and 77 ## , the innermost of which is accompanied by
H# emission enhancement and the outermost also by HI con­
centration, so both are sites of intense star formation (Buta et
al. 1995). Such star forming rings are usually treated as reso­
nance loci of a bar. But morphologically NGC 7217 is a purely
unbarred galaxy; besides, a bar should produce a wave spiral pat­
tern which is not observed in this galaxy. Buta et al. (1995) tried
to solve this problem, through a Fourier analysis of the I­band
image of NGC 7217, and found a modem=2; the conclusion was
that the galaxy has a low­contrast bar aligned along PA # 60 # .
Perhaps, this bar is observed in the late stage of dissolution:
as Athanassoula (1996) has discussed, the rings are more long­
lived than the bars, which may be destroyed by a central mass
concentration. But the most striking peculiarity has been found
by Merrifield &Kuijken (1994): they have claimed the existence
of a counterrotating stellar disk. More exactly, from the anal­
ysis of stellar line­of­sight velocity distribution (LOSVD) data
they noted a counterrotating ``wing'' over the full radius range,
which they have studied, namely from R = 10 ## to R = 60 ## .
This ``wing'' contains 30% of all stars and does not become
weaker with radius; so they conclude that it is not a bulge, but
a counterrotating fraction of the global disk. Immediately, the
question has been raised about secondary gas infall or a minor
merger, though the galaxy looks quite isolated.
We have already studied this interesting galaxy (Zasov &
Sil'chenko 1997): from the ionized gas kinematics in the cir­
cumnuclear region and from an analysis of the central isophotes
we have detected an inclined gaseous disk in the very center of
NGC 7217 and reported a mass concentration of 6 · 10 7 M
# in
its nucleus. During the last years our understanding was grow­
ing on how the phenomena of chemically distinct galactic cores
(Sil'chenko et al. 1992) and kinematically decoupled gaseous
or stellar subsystems in disk galaxies may be related, both be­
ing produced by a secondary gas accretion or minor merger
event. For example, in NGC 2841 we have found a chemi­
cally distinct nucleus, a circumnuclear polar disk of ionized gas
with a radius of 200 pc, and counterrotating stars in the bulge
(Sil'chenko et al. 1997b, Afanasiev & Sil'chenko 1999). The
similarity between the gas and stellar kinematics in NGC 2841
and NGC 7217 has stimulated us to search for a chemically
distinct nucleus in the latter galaxy. The results of this search,
together with additional kinematical and photometric analyses,
are presented in this paper.
2. Observations and data reduction
In 1998 we have undertaken two­dimensional spectroscopy of
NGC 7217 with the Multi­Pupil Fiber Spectrograph (MPFS)
of the 6m telescope of the Special Astrophysical Observatory
(Nizhnij Arkhyz, Russia). Two spectral ranges were exposed:
a blue­green one, 4250--5600 š
A, and a red one, 5650--7000 š
A.
The detailed parameters of the spectral observations are given
in Table 2. A grating of 1200 grooves per mm was used which
provided a reciprocal dispersion of 1.3 š
A per pixel and a spectral
resolution of 3 š
A. The seeing of FWHM=1. ## 6 was estimated
from a stellar exposure.
These spectral observations have been made with the new
variant of the panoramic spectrophotometer which became
operational at the prime focus of the 6m telescope in the
end of 1997. With respect to the previous variants of MPFS
(Afanasiev et al. 1990, Afanasiev et al. 1996), the field of view
is now increased and the common spectral range is larger due
to the use of fibers: they transmit light from 16 â 16 square
elements of the galaxy image to the slit of the spectrograph
(256 fibers) together with the sky background taken 4. # 5 away
from the galaxy itself (6 fibers). The size of one spatial ele­
ment is 1 ## â 1 ## . At the exit of the spectrograph a 1024 â 1024
CCD registers all 262 spectra simultaneously. The primary re­
duction of the data is made within IDL. After bias subtracting,
flatfielding, and one­dimensional spectra extraction from the
CCD frame, we linearize and analyse each spectrum individ­
ually. The one­element spectral characteristics, such as fluxes
in continuum or in emission lines, redshift, and absorption­line
indices are then combined into two­dimensional arrays corre­
sponding to the galactic region under consideration with the
help of software developed earlier in the Special Astrophysi­
cal Observatory (Vlasyuk 1993) and with our own programs.
To calculate absorption­line indices and their errors we have
used also the program of Dr. Vazdekis. As a result, we ob­
tain two­dimensional surface brightness distributions, veloc­
ity fields, and maps of stellar population characteristics. In the
blue­green spectral range, we measure the absorption­line in­
dices H#, Mgb, Mg 2 , Fe5270, and Fe5335 in the popular Lick
system (Worthey et al. 1994); to check the consistency of our
measurements with the model indices calculated in this sys­
tem (Worthey 1994), we also observed stars from their list
(Worthey et al. 1994). Besides that, we use our blue­green spec­
tra to derive a stellar velocity field in the center of NGC 7217
by cross­correlating elementary galactic spectra with the spec­
trum of a K­giant star -- the brighter component of the visual

O.K. Sil'chenko & V.L. Afanasiev: Decoupled nuclei and nuclear polar rings in regular spiral galaxies 481
binary STF 2788. In the red spectral range we have measured
baricentric positions of the emission line [N II]#6583, which is
the strongest in the center of NGC 7217, to derive a velocity
field of the ionized gas. We have estimated the best accuracy of
our velocity measurements as 10 km s -1 from the night­sky line
[OI]#6300 analysis. For the absorption­line index accuracy, we
have made estimates using the method of Cardiel et al. (1998):
the typical error of the indices varies for the EW­like indices
from 0.15 š
A in the nucleus to 0.5 š
A in the individual elements
at the edges of the area investigated, and from 0.004 to 0.01 for
Mg 2 . To keep a constant level of accuracy along the radius, we
summed the spectra in concentric rings centered on the nucleus
and studied the radial dependencies of the absorption­line in­
dices by comparing them to the synthetic models of old stellar
populations of Worthey (1994) and Tantalo et al. (1998). We es­
timate the mean accuracy of our azimuthally­averaged indices
as 0.1 š
A.
Also, we have taken several long­slit spectra of NGC 7217,
which have been obtained at the William Herschel Telescope on
LaPalma with the ISIS, from the ING Archive. The details of ex­
posures are also given in Table 2. These CCD frames have been
reduced with the software of Dr. Valeri Vlasyuk (Vlasyuk 1993).
The photometric data involved in our analysis are taken
from the ING and HST Archives. The broad­band I image of
NGC 7217 has been obtained on June 1st, 1998, at the 1m Ja­
cobus Kapteyn Telescope onLaPalma.The exposure times were
10 min, 10 min, and 5 min, but only the first of the exposures
was well guided; only this is analysed in this work. The seeing
quality is estimated from neighbouring star measurements as
FWHM # = 1. ## 5. The central part of the galaxy has been also
observed by the Hubble Space Telescope. The earlier observa­
tions with WFPC2 were made on June 10, 1994, through the
filter F547M, with an exposure time of 5 min (Principal Inves­
tigator: W. Sargent, Program ID: 5419). Later, it was observed
with the NICMOS2 through the filters F110W and F160W dur­
ing 128 sec each on August 17, 1997 (Principal Investigator: M.
Stiavelli, Program ID: 7331). The spatial resolution was 0. ## 1 for
WFPC2 observations and 0. ## 2 for the NICMOS observations.
We have derived morphological characteristics of the surface
brightness distribution in NGC 7217 by analysing these images.
The program FITELL of Dr. Vlasyuk has been used for tracing
the isophote major axis position angle and ellipticity along the
radius, and 2D image decomposition was performed with the
software FVIZ and IMAR (Vlasyuk 1993) as well as with our
own programs.
3. A magnesium distinct nucleus
and a Fe­rich circumnuclear disk
To study properties of the stellar populations in the central re­
gions of galaxies, we use metal­ and hydrogen­line indices con­
fined to a rather narrow green spectral range, namely, H#, Mgb,
Fe5270, and Fe5335. In the case of NGC 7217 there are some
problems with these indices, however. First of all, rather intense
H# emission is observed in the center of the galaxy, except in
the narrow radial range of R = 4 ## - 6 ## . Therefore one can ex­
pect that the absorption­line index H#, which is a good indicator
of stellar population age, will be strongly contaminated by the
emission almost everywhere and therefore cannot be used. Sec­
ondly, in the nucleus itself a noticeable emission line [N I]#5200
is seen, and as Goudfrooij & Emsellem (1996) noted, this emis­
sion causes an overestimation of the absorption­line index Mgb
because it falls into the continuum band of this index. There­
fore we are forced to use an index Mg 2 which has a broader
continuum base than Mgb, but is more dependent on the correct
calibration of the global spectrum shape. To calculate Mg 2 , we
use galactic spectra calibrated into absolute fluxes.
Fig. 1 shows the isocontours of two­dimensional distribu­
tions of the Lick absorption­line indices, Mg 2 (left) and #Fe# #
(Fe5270+Fe5335)/2 (right) in the central 16 ## of NGC 7217.
The magnesium index is strongly peaked near the nucleus; it de­
creases rather symmetrically with radius, and the shape of outer
Mg 2 contours is not too different from the shape of continuum
isophotes. However, in the very center an elongated structure
seems to appear at the limit of the spatial resolution; it is a bit
shifted to the east from the center of the brightness distribution.
The distribution of the iron index is much more complicated. In
the patchy pattern, one can distinguish an elongated structure of
enhanced #Fe# # (Fe5270+Fe5335)/2, also shifted to the east
from the nucleus and much more extended than the analogous
structure in the Mg 2 map: it can be traced up to R # 5 ## . We
shall refer to it as the `Fe­rich disk'; in the next sections we will
argue that it can be indeed related to the circumnuclear stellar
disk. However, let us note here that the structure with the en­
hanced metal absorption lines is elongated in the south­north
direction whereas the global line of nodes is oriented approxi­
mately east­west (see Table 1).
Lick absorption­line indices have been well calibrated with
respect to the integrated (luminosity­averaged) properties of
stellar populations in numerous works using evolutionary syn­
thesis techniques. Our conclusions derived below are based on
the models of Worthey (1994) and Tantalo et al. (1998) for
single­age single­metallicity stellar populations. Diagnostic di­
agrams of index vs. index are presented in Fig. 2. The diagram
#Fe# vs. Mg 2 (left) is being considered by many specialists in
chemical evolution as a tool to limit the duration of the main star
formation episode (see, e.g., Matteucci 1994). WhenWorthey et
al. (1992) noted for the first time a magnesium overabundance
in most bright elliptical galaxies, this phenomenon was soon
treated as a natural consequence of the short duration of their
star forming epoch, less than 1 Gyr. The nature of this effect is
deduced from the theoretical prediction that magnesium has to
be produced mainly by SNeII, which explode earlier than the
bulk of the iron­producing SNeIa from the same stellar gen­
eration; if the star formation process stops between these two
moments, the stars would have a higher magnesium­to­iron ra­
tio than the solar, which corresponds to continuous star forma­
tion. The star formation histories in the centers of early­type
disk galaxies are less clear than those in ellipticals, and ob­
servational results on their Mg/Fe ratios are also contradictory.
Our statistics (Sil'chenko 1993) showed evidence for a solar
Mg/Fe ratio in the centers of almost all disk galaxies, from Sc

482 O.K. Sil'chenko & V.L. Afanasiev: Decoupled nuclei and nuclear polar rings in regular spiral galaxies
Fig. 1. Two­dimensional maps of the Lick absorption­line indices (isocontours) in the central region of NGC 7217: Mg 2 (left, the outermost
isocontour corresponds to 0.180, the step between isocontours is 0.005) and #Fe# (right, the outermost isocontour corresponds to 2.50 š
A, the
step between isocontours is 0.1 š
A). The gray­scaled background is the distribution of the green continuum.
Fig. 2. Comparison of our observational data for NGC 7217 with the models of Worthey (1994) and Tantalo et al. (1998) for [Mg/Fe]=0. The
ages of the models in the legend are given in billion years. The observational points connected by a dashed line -- bells in the diagram #Fe#
vs Mg 2 (left panel) and circles in the diagram H# vs #Fe# (right panel) -- are azimuthally averages and taken along the radius with a step of
1. ## 0, the bulge points starting from R = 6 ## ; the points for the Fe­rich disk in the left panel are connected from its northern end to the southern
one; unconnected observational points are for individual elements. The metallicities for Worthey's models are +0.50, +0.25, 0.00, --0.22, --0.50,
--1.00, if one takes the signs along the sequences from the right to the left, and for the models of Tantalo et al. they are +0.4, 0.0, and ­0.7. The
mean data for ellipticals of intermediate luminosity on the left panel are taken from Trager et al. (1998).
to S0, in both bulge­ and disk­dominated objects. Jablonka et
al. (1996) reported a strong magnesium overabundance, up to
[Mg/Fe]# +0.5, in bulges brighter than M r # -19.5, includ­
ing our target galaxy NGC 7217. Our data in Fig. 2 (left) differs
from those of Jablonka et al.: here, the nucleus of NGC 7217 lies
near the model sequences of Worthey (1994) implying a solar
Mg/Fe ratio or even a slight iron overabundance. This result is
due to a smaller Mg 2 estimate, 0.25 instead of 0.28 in Jablonka
et al. (1996), but mainly to a higher Fe5335 value, 3.0 š
A instead
of 2.4 š
A. Curiously, the estimate of Fe5270 made by Jablonka
et al. (1996) is quite consistent with ours. We cannot explain
the cause of the agreement in Fe5270 and the disagreement in
Fe5335 but wewould like to note that in model calculations (e.g.
see Worthey 1994) the values of Fe5270 and Fe5335 obtained
are almost equal to each other, as is the case in our data.

O.K. Sil'chenko & V.L. Afanasiev: Decoupled nuclei and nuclear polar rings in regular spiral galaxies 483
The points related to the bulge of NGC 7217 are dispersed
around the model sequences with a solar magnesium--to--iron
ratio, and none of them fall into the area occupied by el­
lipticals of similar luminosity (MB = -19 Â -20), whose
mean locus is plotted using the data from Trager et al. (1998)
(a shaded horizontal band in Fig. 2, left). The azimuthally­
averaged measurements for the bulge also lie along the se­
quences for [Mg/Fe]=0. But the most interesting behaviour is
demonstrated by the points taken within the Fe­rich circum­
nuclear disk. In this rather bright, central part of the galaxy,
the accuracy of the arcsecond element indices, of, say, #Fe#, is
better than 0.3 š
A. The deviations of the extreme points of the
Fe­rich disk at R # 5 ## from the model sequence [Mg/Fe]=0
are at the 3# level, and certainly due to iron overabundance.
This is a rather puzzling observational phenomenon common
for some types of irregular galaxies (e.g. the LMC), and it is
usually treated as evidence for a bursty character of the star
formation (Gilmore & Wyse 1991, Marconi et al. 1994). When
approaching the center of the disk, the Mg/Fe ratio rises and
near the nucleus it becomes close to solar. The total metallicity
of the circumnuclear disk is higher than that of the bulge. Ob­
viously, the Fe­rich disk is a secondary formation product. The
star formation within it had to be strongly inhomogeneous, with
an exotic mechanism to result in iron overabundance at its outer
edge: a kind of transient star forming circumnuclear ring.
As we mentioned earlier, the age diagnostics in the center
of NGC 7217 is complicated by the noticeable Balmer emis­
sion contaminating the Lick index H#. So in the diagram H#
vs. #Fe# (Fig. 2, right) the majority of the observational points
trace only upper limits for the age of the stellar population.
But in the narrow gap between the LINER nucleus and the star
forming ring (see Sect. 5), at R = 4 ## - 6 ## the H# emission is
absent and we can use the H# absorption­line index to estimate
a luminosity­weighted age of the bulge stellar population. From
Fig. 2 (right) one can see that the bulge of NGC 7217 is rather
old, at least 10 Gyr. The ages of the nucleus and of the Fe­rich
circumnuclear stellar disk cannot be determined exactly.
4. Kinematics of stars and gas in NGC 7217
4.1. Circumnuclear region
In the previous paper (Zasov & Sil'chenko 1997) we noted
clear signatures of the dynamical distinctness of the nucleus in
NGC 7217: the rotation axis of the ionized gas inside R # 5 ##
turns by almost 90 # . Now we present further proofs of the ex­
istence of a circumnuclear `polar' gaseous ring (disk?) in this
galaxy.
We now proceed to determine the parameters of the stellar
and gaseous rotation around the nucleus of NGC 7217. Under
the assumption of planar axisymmetric rotation, the azimuthal
dependence of central line­of­sight velocity gradients is:
dv r /dr = # sin i cos(PA - PA 0 ),
where # is the deprojected central angular rotation velocity, i is
the inclination of the rotation plane and PA 0 is the orientation
of the line of nodes, coinciding in the case of an axisymmetric
ellipsoid (or a thin disk) with the photometric major axis. So by
fitting azimuthal variations of the central line­of­sight velocity
gradients with a cosine curve, we can determine the orientation
of the dynamical major axis by its phase and the central angular
rotation velocity by its amplitude. To apply this procedure, we
need two­dimensional velocity fields.
The new MPFS observations allow us to construct two­
dimensional velocity maps for the central 16 ## â 16 ## region
of NGC 7217. Fig. 3 shows such maps for the stars (left) and for
the ionized gas as traced by the [N II]#6583 emission (middle),
as well as the stellar velocity dispersion map (right). One can
see that two velocity maps look different. At first glance, the dy­
namical major axis of the stellar component seems to be close to
the global line of nodes, west­east. However it is strange that the
brightness center coincides with a flat area in the velocity map.
If the dynamical center coincides with the brightness center,
we would obtain a central projected angular rotation velocity
of only (8 ± 2) km/s/arcsec. If we shift the dynamical center 3 ##
to the east, to the point of maximum isovelocity crowding, we
can increase # proj # # sin(i) to (22 ± 5) km/s/arcsec. Fortu­
nately, the direction of the maximum line­of­sight velocity gra­
dient, or the dynamical major axis, remains the same for both
dynamical center locations: it is PA dyn = 241 # ± 2 # within
R = 3 ## , some 30 # different from the line­of­nodes direction,
but coinciding with the PA of the low­contrast bar reported by
Buta et al. (1995). Outside R # 3 ## the dynamical major axis
turns to PA dyn = 276 # , implying an axisymmetric stellar rota­
tion parallel to the symmetry plane of the galaxy. The velocity
map for the ionized gas obtained by measuring the baricenters
of the [N II] emission line (H# is less relevant because of the
underlying absorption line) looks even more striking than that
for the stars. The isovelocities in the very center demonstrate
a strong so­called ``S­shape'' distortion, whose dynamical ma­
jor axis direction changes by 90 # in the radius range of 3 ## --7 ## .
By fitting a cosine curve to the line­of­sight velocity gradients
within 3 ## from the center, we obtain a projected angular rota­
tion velocity of (17±7) km/s/arcsec and a dynamical major axis
PA dyn = -31 # ± 4 # , orthogonal to the dynamical major axis
of the stars in this radius range. Again, we find the signature of
a circumnuclear polar gaseous disk.
The two­dimensional map of the stellar velocity dispersion
in the central 16 ## region (Fig. 3, right) looks somewhat peculiar:
though rather smooth, it demonstrates an elongated `saddle' of
relatively low # # , at about # # # 130 km s -1 , in PA # 60 # and
a slight increase of # # along the kinematic minor axis on both
sides of the nucleus. We have never seen anything like this and
cannot give an interpretation of this map. The dynamical center
which we define here as a center of symmetry of the stellar
velocity dispersion map again seems to be shifted to the east of
the brightness center.
We can check our result on the decoupled rotation of the
circumnuclear ionized gas with the long­slit spectral data from
the ING Archive. Fig. 4 shows line­of­sight velocities measured
from [N II]#6583 and H# emission lines in PA = 68 # and
PA = 150 # . In PA = 68 # , not too far from the line of nodes,

484 O.K. Sil'chenko & V.L. Afanasiev: Decoupled nuclei and nuclear polar rings in regular spiral galaxies
Fig. 3. Two­dimensional line­of­sight velocity fields for the stars (left) and for the ionized gas (middle), and the map of the stellar velocity
dispersion (right) in the central 16 ## â 16 ## of NGC 7217. The gray­scaled background represents the continuum distribution in the green for
the stars and in the red for the gas.
Fig. 4. Long­slit position­velocity cross­sections in PA = 68 # , not too far from the line of nodes, (left) and PA = 150 # (right) for the center
of NGC 7217; [N II] and H# emission line measurements are plotted.
one can see a flat velocity profile segment in the very center,
till ±3 ## from the nucleus, implying that the dynamical major
axis of the circumnuclear ionized gas is aligned orthogonally, in
PA # 158 # (or --22 # ). Outside this central region the gas shows
much larger projected velocities with respect to the nucleus. In
PA = 150 # , consistent with the previous cross­section, the
central part of the velocity profile shows fast decoupled rotation
within ±4 ## from the nucleus with a slope of 24 km/s/arcsec --
evidently, this direction is close to the dynamical major axis of
the circumnuclear gas; outside the radius of 4 ## the projected
rotation velocity falls to a half of the maximum value reached at
the 4 ## radius. Therefore, the long­slit cross­sections confirm the
dynamical distinctness of the central region of NGC 7217 within
a radius of 3 ## --4 ## and the existence of a `polar' circumnuclear
gaseous disk rotating in a plane orthogonal to the global plane
of the galaxy.
4.2. The whole galaxy
Kinematics of the ionized gas in NGC 7217 has been studied
more than once. Long­slit cross­sections along the major axis
were obtained by Peterson et al. (1978), Rubin et al. (1985),
and Buta et al. (1995), and our team also observed NGC 7217
with a long­slit spectrograph and a scanning Fabry­Perot inter­
ferometer at the 6m telescope (Zasov & Sil'chenko 1997). We
have now analyzed the H# and [N II]#6583 emission lines in
the three additional long­slit cross­sections taken from the ING
Archive. The results obtained over the full radius range are quite

O.K. Sil'chenko & V.L. Afanasiev: Decoupled nuclei and nuclear polar rings in regular spiral galaxies 485
Fig. 5. Long­slit cross­sections in PA = 240 # (left) and PA = 150 # (right) of NGC 7217; stellar absorption line measurements obtained by
cross­correlation with the template star spectrum are plotted.
Fig. 6. Long­slit cross­sections in PA = 240 # (left) and PA = 150 # (right) of NGC 7217; stellar velocity dispersions obtained by cross­
correlation with the template star spectrum are plotted. Also the cuts simulated with the MPFS data in the corresponing position angles are
given.
consistent with the velocity curves published previously, and we
do not present the raw velocity data here.
The stellar kinematics in NGC 7217 have received much
less attention than the gas kinematics. Merrifield & Kuijken
(1994) cross­correlated absorption spectra taken along the ma­
jor and minor axes in the spectral range near Mgb#5175 with
those of template s