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INNER POLAR RINGS REGULAR LENTICULAR GALAXIES
1
K. Sil'chenko
2
Sternberg Astronomical Institute, 119992 Moscow, Russia; Isaac Newton Institute Chile, Moscow Branch; olga@sai.msu.su
Afanasiev
Special Astrophysical Observatory, 369167 Nizhnij Arkhyz, Russia; vafan@sao.ru
Received 2003 December accepted February
4
ABSTRACT
have investigated
a sample
of galaxies, mostly with circumnuclear dust lanes orthogonal their major
axes, chosen from Hubble Space Telescope Wide Field Planetary Camera
2 images. Two­dimensional spec­
troscopy undertaken with Multipupil Fiber Spectrograph telescope Special Astrophysical
Observatory Russian Academy Sciences revealed that indeed ionized centers these
eight lenticular galaxies rotate
in planes nearly orthogonal rotation symmetry) planes
of
central stellar components. Although almost galaxies located dense environments, external origin
rotation plane obvious because galaxies one known have extended
H
i disks,
in cases where angular resolution
H
i observations allows, orthogonality external
i
inner ionized disks. discuss
a possible relation inner gas polar rings
a triaxiality
of galactic
potential. stellar populations
in nuclei
of two galaxies are which excludes recent
formation bursts proves polar orbits circumnuclear rather stable. nuclei
of
NGC 2655 and NGC 4111, found signatures formation bursts some 1.5--2 Gyr ago. This finding
be related very central NGC 2655, which coplanar
to circumnuclear stellar radial
inflow NGC 4111; these reservoirs polar rings may responsible fueling nuclear
formation. words: galaxies: evolution galaxies: nuclei galaxies: structure
INTRODUCTION
Lenticular galaxies apparently similar
to elliptical gal­
axies concerning global properties their stellar pop­
ulations: they homogeneously red noticeable
present formation. However, unlike elliptical galaxies,
often possess
a modest amount
of ionized near their
centers; origin quite intriguing problem.
Large efforts solve problem have been applied
F. Bertola with collaborators. They come complex
conclusions. one hand, circumnuclear ionized gas
galaxies
is kinematically decoupled from stellar com­
ponent
in
at 40% cases, which implies
its external
origin (Bertola, Buson,
& Zeilinger 1992). other hand,
velocity dispersion circumnuclear ionized gas
matches well stellar velocity dispersion, sometimes over
extended areas, this evidence internal
origin, say, mass loss from bulge giant (Bertola
et 1995). Here, Bertola
et
al. (1995) make
a note: the latter
mechanism gas supply take place only when stars
ionized gas have coincident rotation
corotating.
is this condition
in necessary? There exist
some paths intrinsic secular dynamical evolution that may
orbit orientations course inflow toward
galactic center,
if belongs initially global
a galaxy rotates global symmetry plane
outer
of example, Friedli Benz (1993)
have calculated
a model self­consistent dynamical evolu­
a three­dimensional stellar­gaseous disk have
found that counterrotating belonging global disk
having antiparallel that the stars, finally
occupies stable orbits strongly inclined
to plane after
approaching center under driving force. resource
counterrotating may intrinsic: counterrotating stars
always present inside
a triaxial potential, they lost
would
be counterrotating. Nevertheless, nothing prohib­
external acquisition counterrotating
though must remember original spin orientation may
quite dissimilar present orientation
center galaxy. mention another possibility
considered detail Van Albada, Kotanyi, Schwarzschild
(1982).
If inner polar exists already within tum­
bling triaxial (stellar?) potential rotation
potential figure the orthogonal, outer parts
gaseous would become warped
by
#
the outermost would counterrotate stellar body.
even
if detect simultaneously inner polar and
counterrotating outer large­scale galactic disk,
would unable choose between them which primary,
the other.
In work, study sample lenticular galaxies with
inner polar rings. Traditionally, rings early­type
galaxies were treated result external accretion---
Kim (1989) about NGC 2768 NGC 4589. We
into doubt such interpretation inner
polar rings some galaxies large amount outer gas
1 Partly based observations collected with telescope
at
Special Astrophysical Observatory Russian Academy
of Sciences.
2 Guest investigator, Astronomy Centre.
2641
Astronomical Journal, 127:2641--2658, 2004
# American Astronomical Society. reserved. Printed U.S.A.

well settled main symmetry planes
of galaxies.
A
phenomenon inner polar rings spiral galaxies
firstly discovered
in nearby galaxy NGC 2841
(Sil'chenko, Vlasyuk,
& Burenkov 1997). Now we know
ready seven early­type spiral galaxies regular global
morphology inner polar rings---five found
and two more Corsini, Pizzella,
& Bertola (2002)
Corsini (2003). Concerning galaxies studied
noted inner gas polar rings spiral galaxies
often accompanied
a presence
of chemically distinct
(magnesium­enriched) nuclei that may treated remnants
secondary nuclear formation bursts, that they
always embedded into triaxial potential being
a global
NGC 4548 (Sil'chenko 2002a),
a mildly triaxial bulge,
NGC 2841 (Afanasiev Sil'chenko 1999),
a lenslike
inner stellar disk---perhaps remnant past
dissolved,
in NGC 7217 (Sil'chenko
& Afanasiev 2000).
However, according Corsini (2003), there galaxies
with inner polar where evidence triaxiality
compelling. How can orthogonal systems coexist? Does
it seem
more probable some intrinsic mechanisms, perhaps,
that described Friedli Benz (1993), could transfer
own galactic disk
a circumnuclear polar orbit?
what about inner polar rings S0's? have found
NGC (Afanasiev Sil'chenko 2000); appears
also inside
a kiloparsec­scale perhaps some
tion extremely young age nuclear stellar popu­
lation,
in bona red quiescent
lenticular galaxy. spectacular feature NGC 7280
predetermined discovery
of inner
in
galaxy: Hubble Space Telescope (HST
) Field Planetary
Camera (WFPC2) image center NGC 7280 revealed
that crossed stellar body very close
nucleus perpendicular major axis. examined
HST/WFPC2 images nearby lenticular galaxies
have found objects prominent circumnuclear
dust rings roughly orthogonal
to major axes inner
continuum isophotes. Among those, galaxies kine­
matical signatures inner gas polar rotation have been
claimed earlier from long­slit observations---in NGC 2768
Fried Illingworth (1994) and NGC 4111 Fisher (1997).
The seventh galaxy sample, NGC 3414,
ular central isophotes according WFPC2 (Rest
2001),
et
al. (2001) nevertheless found
a
lane center
by thorough analysis color distribution,
and orientation
of dust lane
is reported them
again orthogonal galactic major inner
polar eighth galaxy sample, NGC 2732,
is
prominent among others and have been detected
us rather occasionally. All eight galaxies
of sample,
with their global properties taken known extraga­
lactic databases, listed Table
have undertaken two­dimensional spectroscopy
samplegalaxieswith theMultipupilFiberSpectrograph (MPFS),
installed
at prime focus
6 telescope, inspect
things: stars ionized
in circumnuclear regions
these galaxies rotate indeed
in orthogonal planes, and
properties
of stellar populations, mean stellar
first affected some way presence unusual
subsystems
in centers. layout paper follows.
describe observations, data reduction, addi­
tional information which use analysis.
present results: descriptions individual galaxies, general
comparative kinematical analysis
of and ionized
centers sample galaxies, mean characteristics
nuclear stellar populations deduced comparing the measured
(and mapped) indices with evolutionary synthesis models.
Section contains some discussion results concerning
inner polar ring origin, possible role
of establishing
gas orbit orientation, also problem nuclear activity
fueling gas settled
in polar configurations.
a term
``nuclear activity'' includes
as nuclear star formation bursts,
well nonthermal compact nuclear sources.
2. OBSERVATIONS AND DATA REDUCTION
The spectral data analyze work obtained
mostly means two­dimensional spectroscopy. Integral
field spectroscopy
is
a rather new approach
proposed Professor Courtes some ago---for
a
TABLE
Global Parameters Galaxies
Parameter NGC 2732 2768 NGC 2911 NGC NGC 4111
(
a ................................... SAB(s)0/a
S0 S01/2 SB(r)0+ SA(s)0:
S0 SA(r)0+
R
25 (LEDA)
b (kpc) ...........................
B
0
T ....................................... 10.82 12.85 11.61 11.86 11.60
M
B (LEDA) ..................................... #20.96 #19.78 #21.11 #19.39 #20.79 #19.91 #19.34 #19.91
) (RC3) ................................ 0.83 0.94 0.96
(U #B)
0
T (RC3) ................................ 0.42 0.53 0.56
V
r
s
) ......................... 1404 1960 1414 2371
Distance
d .............................. 15.0
Inclination (LEDA) (deg) ...............
90
56
(LEDA) (deg).....................
95 174
v
rot (LEDA, from
H
i)
s
)
.
.
#
* (LEDA)
#1 )....................... 209
H i?..................................................
+
+
+
.
.
Nuclear source? .....................
.
. X­ray X­ray Radio Radio Radio
Environments .................................. Group Group Isolated Group Group Cluster Cluster
NASA /IPAC Extragalactic Database.
Lyon­Meudon Extragalactic Database.
Third Reference Catalogue Bright Galaxies.
distances NGC 2655, 2732,
are LEDA, distances
for 2768, 2787, 3414, 4111
et 2001.
SIL'CHENKO AFANASIEV
2642detailed description instrumental e.g., Bacon
et (1995).
It allows obtain simultaneously spectra
a wide spectral range point
of
an extended area
sky, example, from
a central
of
a galaxy. two­
dimensional array microlenses provides
a micro­
pupils, which onto entry spectrograph, and
having reduced full spectra corresponding
individual spatial elements, obtain
a fluxes
continuum emission line­of­sight velocities,
both stars and ionized absorption­line equiv­
alent widths, which usually expressed indices
well­formulated Lick system (Worthey
et 1994).
transformed into two­dimensional maps above
mentioned characteristics the central galaxy
studied. Besides panoramic view benefits,
approach gives
an unique opportunity overlay various two­
dimensional distributions other without diffi­
culties with positioning.
full spectral exposures obtained
sample galaxies given Table
2. Three different spectro­
graphs used.
two­dimensional spectroscopic observations
of 1998
January were made with variant MPFS
6
m telescope (Afanasiev
et 1990). panoramic view
provided
a microlenses array, and spec­
trum registered with CCD detector
of 580.
spatial scale was microlens. reciprocal
dispersion pixel with spectral resolution
8 slightly varying over the frame. variant
observations, also exposed separately
a blank
arcminutes from galaxy, because needed
subtraction
to calculate properly equivalent widths
absorption lines. The system Lick indices checked
observing standard stars from Worthey
et
(1994); found that index system coincided Lick
within
a mean deviation
Later 1998, new variant MPFS became opera­
tional prime focus telescope.
3 With respect
previous variant, MPFS
of view
increased and common spectral range larger due
to using
fibers: they transmit light from
; square elements
of
galaxy image
of spectrograph together with
additional fibers transmit sky background light
taken apart from galaxy, separate sky exposing
is not
necessary now.
of spatial element
is approxi­
mately
1
00
;
00
a 1024 1024 detector used. The
reciprocal dispersion 1.35 pixel
, with rather stable
spectral resolution
5 invert spectra
wavelength scale, expose separately
a spectrum
hollow cathod filled with helium, neon, and argon;
internal accuracy linearization was typically
8
green and
8
in red, additionally check
accuracy absence systematic velocity
measuring strong emission lines
i] k5577
[O
i] k6300. obtain MPFS data spectral
ranges: green one, covering 4700--5600 wavelength
interval, one, covering 6200--7000 interval. The
green spectra used calculate Lick indices Mg
Fe5270, and Fe5335, which suitable determine
metallicity, age, and ratio stellar populations
(Worthey 1994). They used cross­correlation with
a spectrum
a template usually
of III--K3 spectral
type, obtain line­of­sight velocity stellar com­
ponent map stellar velocity dispersion; typical
accuracy elementary stellar velocity determination km
s
. calibrate MPFS index system onto the stan­
Lick have observed
Worthey
al. (1994) during observational runs and
calculated linear regression formulae transform our
TABLE
2
Spectroscopy Galaxies Studied
Galaxy Exposure (minutes) Configuration (arcsec) (top) Spectral Range Seeing
(arcsec)
Oct NGC
60 BTA/MPFS+CCD
; 1024
;
15 4200--5600
Oct NGC
60 BTA/MPFS+CCD
; 1024
;
15 4200--5600
NGC
30 BTA/MPFS+CCD
; 1024
;
15 5800--7200
Oct NGC
60 BTA/MPFS+CCD
; 1024
;
15 4200--5600
Sep NGC
80 BTA/MPFS+CCD
; 1024
;
15 5800--7200
Oct NGC
15 BTA/MPFS+CCD
; 1024
;
15 4200--5600
Oct NGC
45 BTA/MPFS+CCD
; 1024
;
15 5800--7200
28.......... NGC
60 BTA/MPFS+CCD
; 1024
;
15 4200--5600
19.......... NGC
60 BTA/MPFS+CCD
; 4700--5450
19.......... NGC
60 BTA/MPFS+CCD
; 6200--6900
Oct NGC
30 BTA/MPFS+CCD
; 1024
;
15 5800--7200
Oct NGC
60 BTA/MPFS+CCD
; 1024
;
15 4200--5600
21.......... NGC
60 BTA/MPFS+CCD
; 6200--6900
22.......... NGC
45 BTA/SpN+CCD 1024
;
2
;
34 4500--5800
Dec NGC
75 BTA/MPFS+CCD
; 1024
;
15 4200--5600
22.......... NGC
30 BTA/SpN+CCD 1024
;
2
;
34 4500--5800
31.......... NGC
60 BTA/MPFS+CCD
; 1024
;
15 4200--5600
31.......... NGC
20 BTA/MPFS+CCD
; 1024
;
15 5800--7200
Mar
9 .......... NGC
90 BTA/MPFS+CCD
; 1024
;
15 5800--7200
29.......... NGC
45 BTA/MPFS+CCD
; 1024
;
15 4200--5600
Mar
9 .......... NGC
45 BTA/MPFS+CCD
; 1024
;
15 5800--7200
Mar NGC
60 BTA/MPFS+CCD
; 1024
;
15 4200--5600
Mar NGC
45 BTA/MPFS+CCD
; 1024
;
15 5800--7200
3 http://www.sao.ru/hq/lsfvo/devices/mpfs.
INNER POLAR RINGS 2643
5, 2004

instrumental index measurements into system;
rms scatters points linear dependencies about
0.2 indices under consideration within obser­
vational errors Worthey
et (1994). correct index
measurements stellar velocity dispersion, which
is
usually substantially nonzero the centers early­type
galaxies, have carried smoothing spectrum
standard 97907
a Gaussians various
widths; the derived dependencies index corrections
#
were approximated
by polynomials fourth order applied
measured index values before their calibrations into
Lick system. spectral range that contains strong
emission lines
[
N k6583 used derive line­of­
sight velocity fields ionized
To obtain gas veloc­
ities from the MPFS spectra, calculate wavelength bari­
centers emission lines, mostly
of
[ k6583, which
gives velocity accuracies 10--15
s
1998 January, observed two galaxies, NGC 2911
and NGC 3414, green spectral range with long­slit
spectrograph: called spectrophotometric complex
Nasmith­1 focus
of
m telescope (SpN) supplied with
Photometrics 1024
; used. Although
ciprocal dispersion these spectral observations was
same two­dimensional spectroscopy, pixel
,
narrower instrumental profile allowed
to analyze mul­
ticomponent velocity structure stellar and gaseous
circumnuclear components these galaxies applying
Gauss analysis
to emission­line and correlation­peak
profiles. structure
of central regions galaxies
under consideration compare some characteristic
entations with kinematical data, involve photometric
observational into analysis. give impression
global structures galaxies under consideration,
mostly Digitized Survey images, but Palma
Jacobus Kapteyn Telescope images retrieved Isaac
Newton Group (ING) Archive. reveal
a presence inner
dust/gas polar structures, HST/WFPC2 images:
available HST Archive galaxies
sample except NGC 2732. For NGC 2732, there public
photometric data sufficient quality,
so have undertaken
our observations focal reducer
6
m
scope Spectral Camera with Optical Reducer Photo­
metrical Interferometrical Observations (SCORPIO)
4
under rather good seeing conditions through broadband
VR­ and intermediate­band SED 755 filters; details
observations given Table
3.
In addition, sometimes
lucky retrieve HST/WFPC2 images both through
broadband narrowband filters---it case NGC
2768, NGC 2911, NGC 4111. these galaxies,
obtain maps pure gaseous emission H#+[N
subtracting broadband images properly normalized from
narrowband (F658N) images. Finally, obtain position
angles ellipticity
of innermost isophotes, applied
isophotal analysis reddest HST/WFPC2 images
galaxies (unfortunately, NGC 4111 HST/
NICMOS data), check additionally orientations
outer nodes, analyzed also R­images NGC
2768 from Digital Atlas
et (1996) NGC
3414 ING Archive---the latter minute expo­
sure image, strongly saturated center, which
obtained 1992 May the
1
m Jacobus Kapteyn Tele­
scope (JKT). data, both spectral photometric, except
obtained with MPFS, have reduced with
software produced Vlasyuk Special Astro­
physical Observatory (Vlasyuk 1993). Primary reduction
obtained with new MPFS was done IDL with
a
software created one indices
were calculated with FORTRAN program,
as
using FORTRAN program Vazdekis, which
provides index calculation.
RESULTS OBSERVATIONS
Since integral­field spectroscopy provides
dimensional line­of­sight velocity fields,
probe circularity rotation central structure
galaxies. have axisymmetric mass distribution
rotation
on circular orbits, direction
of maximum central
line­of­sight velocity gradient
it ``kinematical
major axis'') should coincide with nodes
as
photometric major does, whereas
a
of triaxial
potential isovelocities align with principal
of
lipsoid, and generally kinematical photometric major
axes diverge showing turns opposite sense respect
line nodes (Monnet, Bacon,
& Emsellem 1992;
Moiseev Mustsevoy 2000). simple cylindric
(disklike) rotation,
a convenient analytical expression
azimuthal dependence
of central line­of­sight velocity
gradients within area solid­body rotation:
r =dr
!
i cos (P:A:
);
where
!
is deprojected central angular rotation velocity,
i
inclination rotation plane, and P.A.
0 the
entation
of line nodes, coinciding case
axisymmetric ellipsoid
a thin disk) with photometric
major axis. fitting azimuthal variations central
line­of­sight velocity gradients with cosine curve, we
determine orientation kinematical major axis
phase the central angular rotation velocity
its ampli­
tude. This our main kinematical analysis.
The quantitative results this analysis applied
eight lenticular galaxies under consideration presented
Table
4 where we compare position angles
of outer
TABLE
Photometric Observations NGC 2732
Telescope Exposure Seeing (arcsec) (arcsec)
SCORPIO/BTA
1.8
SCORPIO/BTA
1.6
SCORPIO/BTA
1.7
http://www.sao.ru/ hq/moisav/scorpio/scorpio.html.
SIL'CHENKO AFANASIEV
2644isophotes
is, global disks' lines nodes), inner
isophote major axes,
of circumnuclear dust lane ori­
entations, emission­line intensity isophotes, with
kinematical major axes.
give some comments about how orientations
Table have been obtained. orientations lines
nodes some galaxies Table differ from P.A.
0 (phot)
Table this because updated Lyon­Meudon
Extragalactic Database's (LEDA) data: NGC 2655,
have taken NIR P.A.
0 from Mo˜ llenhoff Heidt (2001), and
NGC 2787, quite fresh estimate P.A.
0 from Erwin
Sparke (2003). orientations inner continuum iso­
photes
(it
is
a characteristics stellar component dis­
tributions) have been obtained
by averaging, over radius
range
00
, results isophote ellipse fitting
reddest avoid dust effect) and highest resolution images
among viewed
by orientations kinematical
major axes, both stars for gas, obtained
cosine fitting applied
to azimuthal variations
of line­of­
sight velocity gradients, described above. orientations
nuclear dust lanes taken mostly literature,
references given
in Table orientations
nitrogen emission­line intensity distributions estimated
rough visual inspection nitrogen emission maps, be­
cause small view
of MPFS and irregularities
emission­line isophotes prevent standard ellipse ap­
plication. P.A. estimates least precise
Table with
a typical
of
[
N
]
#
would describe the individual galaxies, and
summarize general impressions.
3.1. NGC 2655
Figure presents
a collection maps giant S0/a
galaxy. outer structure galaxy
is mysterious;
is included into the Atlas (1966). Obviously,
bulge­dominated: Baggett, Baggett,
& Anderson (1998) ap­
proximate full­range brightness profile single
Vaucouleurs' bulge and disk With
creasing photometry accuracy, outer been found,
parameters remain controversial: Mo˜llenhoff
& Heidt
(2001)
¼
76 0:4 from NIR
(JHK
) images, Erwin
& Sparke (2003), R­band
analysis, suggest almost face­on orientation (b=a 0:10,
i
), while measurements are quite uncertain.
00
00 isophote ellipticity profile almost
about 0:7, with P:A:
b
#
#
; however, what
meaning must attach the index ``b''? Erwin Sparke
(2003) doubt
it
is
a ``bar,'' agree: radius range
mentioned above well inside the bulge­dominated region.
Erwin Sparke (2003) right the galaxy
is seen almost
face­on, ellipticity within
00 may signify only
a triaxial bulge.
subtle inner structure, within
R
00
, deduced
solely from HST/F547M data. addition, one see
a noticeable polar (Fig. middle top). may
affect isophote parameter determination; case,
if
inner stellar disk well close face­on orientation
outer disk,
is hope catch photometric sig­
natures against luminous bulge background.
ionized kinematics, previously, from long­slit
observations, guessed that central region
of NGC 2655
something special (Sil'chenko
& Burenkov 1990),
velocity fields
in Figure (right column) revealed even
more complex picture than could suggest. Circumnuclear
rotate rigidly, with P:A:
# taking
count galaxy line­of­nodes orientation and approxi­
mate inner isophote P.A., conclude see axisymmetric
disklike (cylindric) stellar rotation. meantime, gas
kinematical major turns from
2
R
¼
4
00
6
00
; we suggest central ionized gas
rotates together with stars regular circumnuclear
disk?), only the ionized
at
R
00
6 related
polar ring and rotating plane strongly
clined the main symmetry plane galaxy. outer
border
of inner polar ring here marked quite
conventionally because, fact,
it
is beyond MPFS' field
view: our previous long­slit observations (Sil'chenko
Burenkov 1990) evidence polar rotation keeps
00 isophote the nitrogen emission
brightness corresponding
to polar location also
elongated north­south direction, orthogonally
continuum isophote elongation, agreement hy­
pothesis polar ring. Interestingly, extended
large­scale
i distribution shown NGC 2655 Erwin
Sparke (2003)
is elongated 110
#
# strictly
orthogonal rotation plane
00
6
. Does this
contradict their probable common formation external
accretion? index maps central part NGC 2655 rather
featureless. Earlier (Sil'chenko, Afanasiev, Vlasyuk
1992) reported absence chemically distinct nucleus
galaxy, and maps
of Figure
1 (bottom) seem con­
conclusion. Perhaps, unresolved mini­
mum
b center; real, signify either
TABLE
4
Orientation Parameters Galaxies
Parameters NGC 2732 NGC 2768 NGC NGC NGC NGC
P.A.
0 (deg)............
95
P.A.
*
,
2
#
2
#
2
3
#
P.A.
*
,
# 88.5
# (137)
#
2 324
#
#
3
3
P.A.
dust ........
a
.
. #175
b
d
e
e
P.A.
gas, (deg) 45!20(R
4
) #13
#
72
63
#
68
#
7
P.A.
[
N (deg) Round #80 Round Round
& Sparke
Bertola
et
al.
et 2003.
work. 2001.
f 1998.
INNER POLAR RINGS 2645
5, 2004

metal­deficient compact nucleus accreted globular
cluster?), which suppose
to quite improbable,
extreme youth the nuclear stellar population. Below
show latter
is
2732
This lenticular galaxy
is seen edge­on. Although bright
and nearby, has attracted attention other
members our sample;
in particular,
it lacks HST data.
However, ground­based investigations photometric
structure stellar kinematics undertaken. Both
Seifert Scorza (1996) and Baggett (1998), formers
basing two­dimensional photometric analysis
ters basing major­axis V­brightness profile decomposition,
have found global stellar the galaxy has
a
center, within
R
#
00
; such disk profiles often
met barred galaxies, although NGC 2732
is not classified
barred. Hence not expect find
a circumnuclear stellar
disk this galaxy. nuclear emission lines weak
confined
to central galaxy,
so
as know
gaseous kinematics 2732 were investigated
before work.
Our photometric obtained with reducer
6
telescope SCORPIO have revealed
a presence large
spots near minor
of edge­on galaxy (Fig.
middle); taking into account lack significant amount
gas galaxy (Haynes
et 1990), these off­plane
relatively recent formation quite strange. Two­
dimensional velocity fields stellar ionized
components (Fig. right column) solve puzzle partially.
The galaxy demonstrates orthogonal rotations stars
and
N
ii] emission isophotes elongated accordance
kinematical major axis, deal with inner
polar stars rotate quite axisymmetrically: although
isophote major bulge deviates from
nodes some
#
# ---it firm photometric conclusion,
full agreement with photometry Seifert
& Scorza
(1996)---the stellar kinematical major axis turns together
The stellar velocity dispersion demonstrates peak
center agrees with the absence circumnuclear stellar
disk. Obviously, stellar component which axisymmetric
rotation we observe bulge
of NGC 2732.
addition, absence circumnuclear stellar
NGC 2732 disfavors
a presence chemically distinct
cleus. Indeed, metal­line index distributions bottom)
rather flat, rather low levels galaxy's stellar
locity dispersion total luminosity.
2768
another galaxy
in sample, besides NGC 2655,
lacks perhaps
a global disk:
in some catalogs (e.g., RC3),
it
classified Kent (1985) fitted brightness profile
a
single Vaucouleurs' law, Peletier (1990) found
practically constant orientation
of isophote major
about
#
#
. However, have undertaken
our own isophote analysis images
1.---Maps
for 2655. row: Large­scale photographic view small­scale HST image, where selects
an observed
in
with MPFS. Bottom row
( from
to right):
of Lick indices hFei [#(Fe5270 Fe5335)/2]
of velocity dispersion; isophotes
show green continuum distribution. Right column
( bottom): Nitrogen­emission isophotes overlaid
red continuum gray­scaled velocity
fields ionized and
of
the component given isovelocities overlaid
the gray­scaled continuum distributions. orientation maps
is
same, northeast directions shown corner large­scale image.
SIL'CHENKO AFANASIEV
2646NGC 2768 retrieved from Digital Nearby Gal­
axies Frei
et (1996), have obtained persistent trend
isophote major axis P.A.
to optical border
galaxy, from
#
at
R
¼
00 P:A:
0
#
R
¼
00 variations isophote ellipticity not
quite smooth, having
a ``knee''
at maximum
R
¼
00 with
a subsequent even NGC 2768
spheroid, probably
a triaxial one.
In center NGC 2768, Fried
& Illingworth (1994)
reported polar rotation ionized
00
confronting their major­axis minor­axis long­slit spectra.
Moreover, even before the epoch, some investigators no­
ticed
a minor­axis lane near nucleus (Kim 1989). With
HST data, indeed, have clearly seen
a system wrap­
dusty rings orthogonal the continuum isophote major
3, middle) and subtracting normalized red
continuum image from the narrowband one (WFPC2/F658N),
have even obtained picture
a spiral the circum­
nuclear polar (top right insertion). Two­dimensional
central velocity fields reveal regular rotations---a polar one
ionized
a slow one confined
to symmetry
plane galaxy central stellar component. stellar
velocity dispersion map demonstrates prominent minimum
center, which also
in long­slit data Simien
Prugniel (1997) Neistein
et (1999) which may
explained
a presence
a compact circumnuclear stellar
disk. slow visible rotation central stellar component
a lack photometric signatures the embedded disk
presence HST data may attributed nearly face­
orientation
of disk---it also consistent with
roundish shape
of the stellar velocity dispersion minimum area
(compare, view edge­on circumnuclear
in 4111,
metal­index maps center
of NGC 2768 show
prominent magnesium
in nucleus quite flat
distribution index.
It
is typical chemically distinct
nucleus related perhaps
to the circumnuclear stellar Since
confronting hFei
[
# (Fe5270
+ Fe5335)/2]
maps reveal increased magnesium­to­iron ratio
nucleus, secondary formation burst having produced
circumnuclear stellar disk was probably short, longer
a few hundreds megayears.
3.4. NGC 2787
It
is smallest least luminous galaxy our
sample: optical radius only
3 and
is quite
a safe
estimate because the distance NGC 2787 known from
direct measurements surface brightness fluctuations
Tonry (2001). galaxy
is unique
in many senses
among objects our sample: only NGC
is quite
isolated others groups clusters), NGC 2787
is previously classified
a bona barred galaxy (SB0).
Erwin
al. (2003) recently analyzed photometric
structure and have found two exponential disks different
2.---Maps NGC 2732. Large­scale CCD through intermediate­band obtained SCORPIO/BTA (V#R)
obtained same photometer (the zero
is arbitrary, right), where inner square selects observed green MPFS.
Bottom
to right): Lick indices hFei [(Fe5270
+ Fe5335)/2] stellar velocity dispersion; isophotes show green
continuum distribution. column
( from bottom): Nitrogen­emission isophotes overlaid continuum gray­scaled, velocity
of ionized
stellar component isovelocities overlaid gray­scaled continuum distributions. The orientation maps
is and
northeast directions shown corner large­scale image.
INNER POLAR RINGS 2647
5, 2004

scale lengths, inner which truncated
at
R
#
20
00
,
and which harbors
a ending
at
R
#
30
00
.
Such decomposition leaves little room for
a bulge, which
seen only
R
#
00 above bulge profile
is fitted
a Sersic with which quite atypical early­
type disk galaxies having usually Vaucouleurs' bulges.
outermost part galaxy looks also strange:
it reveals
large neutral­hydrogen beyond the optical bound­
aries galaxy. This ring mapped Shostak
(1987): although shape was found roundish,
it rotated
spectacularly, the kinematical major rotation,
P:A:
5
, suspiciously reminiscent bar
entation,
¼
# (Athanassoula 1990).
one check really bar?
Figure presenting our data collection NGC 2787
demonstrates, among other maps, spectacular dust rings
center NGC 2787, which become
of most
famous public pictures HST/WFPC2. Erwin
& Sparke
(2003) have found orientation P:A:
#
#
rings; however, MPFS nitrogen emission isophotes
elongated P:A:
½
#
#
#
, kinematical major
axis, P:A:
g
#
#
, consistent rather
to latter orienta­
tion circumnuclear gaseous disk. any case, inner
ionized gas disk polar with respect orientation
(and with respect outer
i ring), respect
stellar rotation proceeds strictly axisymmetrically,
main plane stellar disks 2787. The stellar
velocity dispersion
of NGC 2787 looks rather
of extended maximum elongated bar direction
that predicted models barred galaxies---see,
Vauterin Dejonghe (1997).
The metal­line index maps again demonstrate
a magnesium­
enhanced, chemically distinct nucleus,
as NGC 2768;
index distribution looks more homogeneous than
the magnesium index. However, NGC 2787
b
peak slightly shifted respect brightness peak,
whole magnesium­enhanced structure elongated
north­south direction, P:A:
# 160
#
, again suspiciously
close
to orientation.
2911
Unlike previous object
, which smallest galaxy
sample, NGC 2911
is largest galaxy
of sample;
and NGC 2787
is
a bona barred galaxy, NGC 2911
the only galaxy sample where signs
were noted. Moreover, Jungwiert, Combes, Axon (1997)
have deprojected image and have concluded
NGC
is certainly unbarred. The global morphology
galaxy (Fig. would called quite regular
unless
a noticeable amount dust were projected onto
southwestern Perhaps, dusty medium forms
a
polar the center the galaxy: HST/WFPC2
broadband image reveals
a lane orthogonal
to
isophote major HST/WFPC2 narrowband,
3.---Maps
for 2768. row: Large­scale photographic small­scale HST image, where square selects area observed
in
green MPFS. latter, insertion presents
a ``pure­emission'' Bottom
( from right):
of indices
b hFei [(Fe5270
+ Fe5335)/2] stellar velocity dispersion; isophotes continuum distribution. column
( from bottom):
Nitrogen­emission isophotes overlaid continuum gray­scaled, velocity fields ionized stellar component
by isovelocities
overlaid gray­scaled continuum distributions. The orientation
is same,
the northeast directions
are shown
at
of
scale image.
SIL'CHENKO AFANASIEV
2648continuum­subtracted image reveals ionized emission
reminding
a edge­on disk (Fig. top middle).
ionized­gas velocity fields shown Figure
(right column) demonstrate expected orthogonal rotations:
rotate axisymmetrically, with their kinematical
major axis strictly aligned with photometric major
with line nodes
of outer disk, whereas
kinematical major axis
is consistent orientation
N
ii] emission isophotes. However, there slight dis­
crepancy
in self­consistent picture: the visible angular
rotation speed stars,
# sin
i
#
#
8
s arcsec
#1
much slower than
of
!
i
arcsec
, although their velocity dispersions equal. Since
galaxy modestly inclined,
# (LEDA), incli­
nation factor,
#
, cannot explain discrepancy. can
suggest another explanation inspecting Figure
6 where
compare long­slit velocity profiles NGC 2911
obtained with SpN/BTA simulated sections
derived from two­dimensional MPFS velocity fields.
average, they agree; however, higher spectral resolution
SpN allows separate stellar velocity components
of which quite consistent with the velocity mea­
surements demonstrates much faster rotation than
it
is implied spectrally unresolved MPFS Since
these stellar components counterrotate apparently
cross section position angle,
¼
, being co­
added, they provide almost zero line­of­sight velocity gradient
across nucleus. Obviously, stellar velocity field
obtained MPFS
a superposition two
stellar subsystems:
is central part stellar disk
NGC 2911, other perhaps related inner
polar that fact, stellar gaseous one. Hence
NGC 2911 represents perhaps certain case where
inner polar disk originates from minor merger and where
material inner polar disk probably debris gas­
dwarf galaxy cannibalized NGC 2911.
center NGC 2911 (Fig. bottom again harbors
a magnesium­enriched chemically distinct nucleus,
index map, although quite homogeneous, demon­
strates prominent features. The peak slightly dis­
placed southwest from photometric center, this
displacement may consequence asymmetric dust
distribution; continuum isophote crowding the southwest
from center confirms this hypothesis.
3.6. NGC 3414
It
is most mysterious object our sample. large­
scale morphology
7, left) looks unusual Arp
(1966) included
it Atlas Peculiar Galaxies
162, and Whitmore
et (1990) even suspected have
a large­scale polar ring. Indeed, large­scale view reveals
roundish main body seems
to
a prominent bulge from
first glance,
a thin disk seen edge­on along
#
at radii. However, quantitative analyses
radial brightness profiles---in
V Baggett (1998)
band Chitre (2002)---have shown
4.---Maps NGC Large­scale photographic
a small­scale image, where inner square selects observed green
MPFS. Bottom
to right): Maps Lick indices [(Fe5270
+ Fe5335)/2] stellar velocity dispersion; isophotes
the continuum distribution. Right column bottom): Nitrogen­emission isophotes overlaid continuum gray­scaled, velocity fields
of ionized
of stellar component given
by isovelocities overlaid gray­scaled continuum distributions. orientation maps
northeast directions shown corner large­scale image.
INNER POLAR RINGS 2649
5, 2004

main body exponential brightness distribution,
main roundish
is face­on global stellar
NGC 3414;
a Vaucouleurs' bulge, exists
is
tiny, with effective radius only
8
. Then
``edge­on'' outer structure treated, more
probably, very long bar, nevertheless, large­scale
polar (?). Large­scale velocity fields 3414
strongly needed answer question. for central
NGC 3414, there HST/WFPC2 data, none
reveals any spectacular similar those seen
most other galaxies
of sample. However, Tran
(2001) having constructed quasi­(V#I
) map from F814W
and F555W report detection dust lane red lane'')
P:A:
. constructed color map
central part NGC 3414 ourselves (Fig.
7, middle); from
our point view, nice
is
seen, not P:A:
#
in P:A: dust
#
.
ring strongly inclined
to sight, not
.
The rotation, although confined
to very central
the galaxy,
R
<
5
, however, fast, kinematical
major axis, P:A:
3
, consistent with the
pothesis ionized rotates within
detected Meanwhile interpretation the stellar
velocity not straightforward. center
of stellar
rotation marginally shifted 1B5--2
00 southwest from
photometric center, taking account modest
amount the circumnuclear dust and distribution,
it
not effect screening; similar shift dem­
onstrated maximum stellar velocity dispersion
(although rather extended). kinematical major
stellar velocity field, P:A:
¼
# (144
#
6
,
though almost orthogonal the kinematical major axis,
however strongly discrepant relative photometric
5.---Maps
for 2911. row: Large­scale photographic small­scale HST image, where square selects area observed
in
green MPFS. latter, insertion presents
a ``pure­emission'' Bottom
( from right):
of indices
b hFei
[ (Fe5270 Fe5335)/2]
of
the velocity dispersion; isophotes show green continuum distribution. column
( from bottom):
Nitrogen­emission isophotes overlaid continuum gray­scaled, velocity fields ionized stellar component
by isovelocities
overlaid gray­scaled continuum distributions. The orientation
is same,
the northeast directions
are shown
at
of
scale image.
6.---One­dimensional velocity profiles obtained NGC 2911
long­slit SpN/BTA (N­1) simulated from two­dimensional MPFS
velocity fields---both
in
#
.
SIL'CHENKO AFANASIEV
2650major axis
to line nodes
of global (both
at 179
#
). This turn kinematical
major axis cannot directly related triaxial structure
because innermost isophotes show turn with respect
global­disk ones. have some weak hints, from our
long­slit spectroscopy with SpN, that stellar velocity field
obtained with MPFS and presented Figure
7 fact
a superposition contributions from stellar subsystems.
Figure
8 presents
a comparison long­slit cross section
P:A:
# obtained with cross section
simulated MPFS
in same position angle---
similarly
to Figure
6 2911. section
simulated from MPFS panoramic data
in general
agreement with long­slit cross section from SpN:
demonstrate kinematical decoupling between the stars
the ionized However, higher spectral resolution
SpN data allowed
us
to decompose stellar line­
of­sight velocity distribution south center,
R
¼
10
00
, counterrotating components. would
point that, unlike situation NGC 2911,
in NGC 3414
second stellar component nothing inner
polar ring; above detected
in
a single
particular location---between
00
R
southwest from nucleus. Further high­resolution spectral
observations needed
to clarify exact localization
origin counter­rotating stellar subcomponent this
galaxy.
chemically distinct, magnesium­enriched
NGC 3414 (Fig. bottom resembles NGC 2787:
it
is extended major axis, but
its elongation
is aligned the projection
of inner polar ring. The iron­
index map, although very homogeneous, demonstrates
7.---Maps NGC 3414. Large­scale CCD through
R obtained
at JKT/La Palma
a small­scale
continuum isophotes overlaid, where large square selects
an observed green MPFS. central latter image (small
square) expanded
in insertion. Bottom
( from right): Maps
of
the indices
b hFei
[ (Fe5270
+ Fe5335)/2] stellar
velocity dispersion; isophotes show green continuum distribution. Right column
(
to bottom): Nitrogen­emission isophotes overlaid
the
continuum gray­scaled, velocity fields ionized
of stellar component given isovelocities overlaid onto gray­scaled continuum distributions.
orientation
of same, northeast directions shown
at
the corner
of
the large­scale image.
8.---One­dimensional velocity profiles obtained
for with
long­slit SpN/BTA simulated
the two­dimensional MPFS
velocity fields---both
¼
#
INNER POLAR RINGS 2651
5, 2004

features connected extended magnesium­enriched
core. NGC 4111
This edge­on lenticular galaxy
is rather well studied. Some
years Fisher (1997), from long­slit observations,
reported polar rotation
in center
of NGC 4111. From
photometric point view, Seifert Scorza (1996) found
a
separate stellar disk, and Souza
& Anjos (1987)
listed bulge
of NGC 4111 boxy one. major­axis
surface brightness profile was decomposed into
a
of
a
single exponential single Vaucouleurs' bulge
(with
r
e only 2B5) Baggett (1998): global stellar
disk NGC dominates total surface brightness
R#
. However, inner stellar
is clearly
R
00 middle). The polar
also reported previously Barth (1998) from
HST/WFPC2 data. plotted F702W
continuum map where can polar ring,
narrowband, continuum­subtracted HST/WFPC2/F658N
map where emission­line intensity distribution would
seen (Fig. middle, right insertion). Curiously,
map one see rather polar
in absorption
probably,
a rather young (#1 stellar popu­
lation
is embedded inner With
MPFS, mapped separately
[ k6583 emission
line intensity, which
is affected absorption
(Fig. right). have not seen anything elongated
aligned with polar projection; center
emission brightness distribution clumpy, suspect
presence
of ionized­gas subcomponents,
sides the inner polar ring.
Star velocity fields
in center
of NGC 4111
very regular (Fig.
9, right column). However, whereas
stars rotate quite axisymmetrically, kinematical
major coincident with photometric one, and
typical ``pointed'' shape their isovelocities confirms
presence compact inner stellar velocity
field cannot easily interpreted. regular cylindric
rotation---far beyond dust polar ring area---demonstrates
kinematical major kin;g
, exactly
between line nodes stellar disk and
polar plane. modest intensity the emission
lines moderate spectral resolution MPFS
observations prevent attempts
to separate different
eous subsystems data. only suggest
any case---either there two subsystems with different
rotation planes,
is gas subsystem
strong radial motions---the inner polar
in NGC
is
not stable, most galaxies sample,
so
there are opportunities nucleus from
polar
9.---Maps
for 4111. Large­scale view through
R filter obtained JKT/La Palma
a small­scale
inner square selects observed
in green with MPFS. latter, right insertion presents ``pure­emission'' (see text). Bottom
right): Maps indices
b
# (Fe5270 Fe5335)/2]
of stellar velocity dispersion; isophotes show green continuum
distribution. Right column
( bottom): Nitrogen­emission isophotes overlaid continuum gray­scaled, velocity fields ionized
of
stellar component given isovelocities overlaid onto gray­scaled continuum distributions. orientation
of same, northeast
directions
at
of
the large­scale image.
SIL'CHENKO AFANASIEV
2652Lick index distributions
in 4111 (Fig. bottom)
much more understandable ionized velocity
field. Here
a ``classic'' disk­shaped variant
chemically distinct core more than once---in
NGC 1023 (Sil'chenko 1999a), NGC 7331 (Sil'chenko
1999b), NGC 7217 (Sil'chenko Afanasiev 2000), etc.
magnesium­enhanced core compact, hardly resolved,
whereas maximum represents extended co­
incident with photometric inner region. index
distribution shown Figure
a disklike pattern.
Such combination index distributions implies secondary
formation burst circumnuclear region some Gyr
geometry which was disky, brief intense
explosion
in center more prolonged process
at
periphery
of circumnuclear disk. The quantitative char­
acteristics circumnuclear stellar population NGC
4111
be discussed below.
3.8. NGC 4233
regular lenticular galaxy (Fig. top left),
a member
Virgo Cluster,
is very studied. There two
dimensional structure analysis surface brightness
profile decomposition, Gavazzi (2000) noted expo­
nential bulge
is untypical for early­type galaxy,
Baggett
et (1998) fitted global
a Type
profile, exponential hole center,
at
R
<
00
. latter feature implies possible presence
a indeed, LEDA marks NGC 4233 with sign
``B,'' meaning ``barred.'' central part, there
HST/WFPC2 data galaxy, top
middle)
a dust polar ring, this strictly edge­
The nitrogen emission isophotes (Fig. right)
strongly elongated direction lane, sup­
porting hypothesis polar gas­dust disk. addition,
velocity field plotted below demonstrates rotation
kinematical major exactly aligned the polar
projection. stellar rotation (Fig. bottom right), although not
however, regular too. kinematical major axis
deviates slightly, some
#
, nodes. How­
ever, innermost (F702W) isophotes homologous
outermost isophotes
of global stellar disk, would
suggest
a presence stellar disk slightly disturbed
perhaps intermediate­scale HST/WFPC2
image isophotes changes from 174
#
00 same
is orientation outer nodes) #200
#
at
R
¼
00
stellar velocity dispersion distribution demonstrates
feature rather common galaxies
of sample:
elongated maximum, aligned isophote major but
shifted respect the photometric center. have not
found
a plausible explanation asymmetry.
metal­line index maps (Fig. bottom reveal
presence mild magnesium enhancement near nucleus;
feature seems
to extended elongated direc­
the polar ring. have already seen something similar
NGC 3414.
10.---Maps NGC 4233. row: Large­scale photographic view
a small­scale image where inner square selects observed green
MPFS. Bottom
( right): Maps
of indices
b
[ (Fe5270
+ Fe5335)/2] stellar velocity dispersion; isophotes
the continuum distribution. Right column bottom): Nitrogen­emission isophotes overlaid continuum gray­scaled, velocity fields
of ionized
of stellar component given
by isovelocities overlaid gray­scaled continuum distributions. orientation maps
northeast directions shown corner large­scale image.
INNER POLAR RINGS 2653
5, 2004

Kinematical Summary
The interesting common property sample
axies that evident from Table the orientation
inner continuum isophotes coincides with line nodes
cases: maximum deviation,
8
# within
termination accuracy. regularity looks rather unexpected
into account that according
to LEDA four galaxies
large­scale
If compare P.A.
*
,
and P.A.
*
, axisymmetry galactic central
regions,
a good agreement character­
istics too. Figure presents
a convenient
to inspect
this issue. Four galaxies---NGC 2655, 2732, NGC 2911,
and NGC 4111---lie exactly
at P:A:
#; straight
line, for these galaxies claim axisymmetry
central structure rotation. Three galaxies slightly
``axisymmetry locus,''
by some
# --15
#
, one, NGC
3414, strongly P:A:
#;
. Among
those, NGC 2787, NGC 3414, NGC 4233 barred
according LEDA. NGC 2768, we conclude that
main spheroidal body NGC 2768
is triaxial,
so
galaxy
be related barred subsample. shift
barred subsample with respect the axisymmetry locus
Figure gives evidence for global influence
circumnuclear stellar kinematics.
comparison
of kinematical major axes dust
emissive distributions shows they generally
aligned almost cases, deal indeed with regularly
rotating polar subsystems---rings disks. NGC 2655,
certain ring, because ionized inside
00
rotates together with precise sizes these inner
polar rings/disks difficult estimate
in work because
they exceed often size MPFS field view; from
results earlier long­slit observations, NGC
NGC have radii least
00 However,
among galaxies, there certain case where mutual
P.A.
,
, P.A. orientations
so clearly
related: NGC 4111.
In galaxy, almost surely
suggest that radial motions may exist because significant
potential symmetry plane center
or strong
potential triaxiality excluded: galaxy seen edge­
central compact stellar disk aligned with outer
one clearly detected (Seifert Scorza 1996).
one case, namely, 2911, found some
signatures that inner gas polar ring contain some
stellar population that shares polar rotation. Taking
account the asymmetric distribution ``external''
it
probable candidate minor merger.
3.10. Stellar Population Properties
With the Lick indices
b, hFei [#(Fe5270
+
Fe5335)/2] measured, estimate important charac­
teristics
of stellar populations---magnesium­to­iron ratios
that characterizes duration
of main formation event
and luminosity­weighted ages---by confronting our observa­
tions
to evolutionary synthesis models. keep constant
(high) level index measurement accuracy along radius,
that constant signal­to­noise ratio, summed
mentary galactic spectra
in concentric centered onto
nuclei studied the radial dependencies
of absorption­
line indices. estimate typical accuracy our azimuth­
ally averaged indices
known elliptical galaxies mostly magnesium
overabundant, ½Mg=Fe# 0:3
# (Worthey, Faber,
Gonza ’lez 1992), whereas disk galaxies, including lenticulars,
tend have solar Mg/Fe ratios (Sil'chenko 1993). Modern
chemical evolution models relate Mg/Fe ratios
a duration
star formation events, nuclear Mg/Fe ratios
temporary characteristics nuclear star formation bursts
(secondary primary). Figure presents (Mg hFei)
diagram where compare azimuthally averaged index
measurements with evolutionary synthesis models.
recently, models could calculated only solar
Mg/Fe; such classic Worthey (1994) models. How­
ever, now attempts already undertaken
to expand
evolutionary synthesis supersolar Mg/Fe ratios.
Figure have plotted quite fresh model calculations
Thomas, Maraston,
& Bender (2003) ½Mg=Fe#
¼ +0.3,
and +0.5 stellar ages each,
T
comparison, model
of Worthey (1994) ½Mg=Fe#
0:0 Gyr also plotted
to demonstrate
a stability
model results stellar physics different these
model sets). The nuclei galaxies plotted
largest signs, then sizes signs diminish when
lated radial zones farther farther from centers.
can our sample galaxies demonstrate different
havior. The nuclei
of NGC 2655 and NGC 2732 have solar
Mg/Fe ratio, NGC 2787 another extremity:
nuclear
½Mg=Fe## ×0:5. The sample nuclei
between extremities: ½Mg=Fe# ×0:3 0:1
``bulges''---off­nuclear azimuthally averaged measurements---
seem more homogeneous family than nuclei:
bulges have ½Mg=Fe# ×0:3 0:1
clude despite presence absence
of
a resolved
cumnuclear disk, intermittent star formation often takes place
unresolved nuclei
of galaxies.
determine mean luminosity­weighted
circumnuclear stellar populations galaxies under
sideration, Balmer absorption­line index which
especially sensitive this characteristics. Although
carefully calibrate index measurements
11.---Graphic presentation comparison between orientations
kinematical photometric major axes, taken
respect
to global lines nodes values
,
,
0
from Table dashed straight lines relations
y
x
y
SIL'CHENKO AFANASIEV
2654system through observations standard stars, we also
to make additional check index accuracy
comparing azimuthally averaged radial index profiles with
precise well­calibrated long­slit literature.
example such comparison
is presented
in Figure 13.
compare azimuthally averaged index variations
NGC 4111 long­slit measurements along major and
minor axes Fisher, Franx, Illingworth (1996). one
expect, long­slit profile corresponding azi­
muthally averaged data minor­axis long­slit
measurements along major axis polluted edge­
circumnuclear stellar disk (see Fig.
NGC 4111), which obviously much younger than bulge
so demonstrates
a homogeneously high absorption­
index level. However, the agreement between azi­
muthally averaged profile minor­axis long­slit
measurements Fisher (1996)
in
is good,
as agreement three circumnuclear estimates
and Fisher canonical aperture
00
4
00
) Lick H# value from Trager
et (1998). Besides
profile NGC 4111, Figure also H#
profile NGC 2787
to demonstrate stability index
calibrations into system. observations
of NGC
2787 have been made quite different MPFS units,
even spectral instrumental contours differ substantially; nev­
ertheless, calibrated profiles coincide.
central part profile NGC 2787 reveals,
meantime, one serious problem with index: compared
model calculations, index values are unrealisti­
cally
It because they contaminated emission
from ionized Below shall eliminate this
effect least azimuthally averaged indices
determine mean (luminosity­weighted)
stellar populations various distances from center
galaxies. We estimate
a possible emission contribution
the equivalent width (which fact, index)
measuring emission­line equivalent width the same
spatial element spectrum. Intrinsic emission­
intensity ratio
is studied:
it
is about pure
radiative excitation young stars (by blackbody
spectrum) much more shock excitation
ionization power­law spectrum. Recently, Stasinska
Sodre
’ (2001) have established excellent correlation
EW(H#) 0:25EW(H#) integrated spectra over
a mor­
phologically heterogeneous sample nearby galaxies; use
relation corrections measured indices. We
have co­added the MPFS spectra sample galaxies
concentric rings centered onto
a nucleus have measured
mean variations
of EW(H#
) along radius ap­
plying
a Gauss analysis the emission profiles co­
added spectra separate Balmer H# kk6548,6583
emission lines;
an absorption line included
Gauss decomposition. Since emission­line ab­
sorption­line widths often different, Gauss decompo­
sition successful
in most cases. Figure
compare results EW(H# measurements
in
nuclei those Ho, Filippenko,
& Sargent (1997).
et (1997) attempt separate emission and
absorption lines Gauss analysis, instead they subtracted
template spectra
, which without emission lines. However,
13.---Radial profiles azimuthally averaged index Top:
Comparison
of data obtained
for 2787 different variants
MPFS. Bottom: Comparison
of azimuthally averaged data NGC
with long­slit Fisher
et
al. (1996). aperture measurement
of Trager
et
al.
is also plotted.
12.---The ``iron magnesium'' diagram azimuthally averaged
measurements. data points radius galaxies
1
00
, size
of diminishes
it farther
center. nuclear
are supplied with error
typical accuracy
of
the off­nuclear azimuthally averaged indices
is
8.
stellar population models Thomas (2003) different magnesium­
to­iron ratios three different
are plotted reference; small signs
model curves mark metallicities
of +0.35, #0.33,
#1.35, #2.25,
if
to bottom. One
model curve Worthey (1994) ½Mg=Fe#
¼
0
T
is also
plotted stress general agreement different model
calculations
INNER POLAR RINGS 2655
5, 2004

agreement between their results
is rather satis­
factory: three galaxies demonstrate exact coincidence
three galaxies
et (1997) EW(H#
) estimates
higher
8 than ours. Among latter galaxies there
NGC NGC 4111. shall below, nuclear
stellar populations these galaxies very young, even
uncertainty
of index cannot change this fact---
increase corrections emission
axies, would decrease their further. NGC
2911, where emission
is strongest sample,
mind that estimate EW(H# emis
)
galaxy may and consequently estimate
H# absorption­line index this galaxy also
some #0.5 estimate nucleus
NGC given below
is overestimated.
Mg/Fe ratio varying within
a single galaxy,
as
a
Mg/Fe ratio varying within sample, creates difficulties
choice age­diagnostic index­index diagram: confronting
either hFei H#, can obtain different
mates. wisest choice metal­line index
situation ½MgFe# bhFei
Ï
÷ ---e.g., Gonza (1993)
Terlevich Forbes (2002): using combined [MgFe]
index, minimize the Mg/Fe ratio influence
determination. Figure presents age­diagnostic diagram
H# versus [MgFe]; sure about negligible effect
Mg/Fe ratio estimates, have plotted two model
sets, models
of Worthey (1994) ½Mg=Fe#
¼
0 and
models Thomas (2003) ½Mg=Fe#
¼ ×0:3. Since
have chosen combined index [MgFe] metallicity
discriminator and since models
of Worthey (1994)
Thomas
et
al. (2003) demonstrated their consistency
Figure general, must consistent metallicities
higher than
# would expect that both diagrams
same estimates; indeed,
is case.
nuclei, NGC 2655 and NGC 4111, are obviously young,
with the mean stellar population ages about
2
nucleus,
in 2732, intermediate
of about
8
The other nuclei certainly old,
T# Gyr. NGC
2911, radially varying index estimates,
below even sequence Gyr; increase
index correction
8 above), nucleus NGC
2911 would
at sequence
of 15--17 Gyr, together
other nuclei. increase the nuclear indices
NGC NGC 4111
to their EW(H# estimates
into agreement with results Ho (1997),
mate their nuclear mean stellar would decrease only
some Gyr. bulges sample galaxies
the radial variations
of stellar population
properties NGC 4111
to
T#
12 only
R#
5
00
,
which consistency with the border
of circum­
nuclear stellar that despite data
in Figure
azimuthally averaged.
4. DISCUSSION
have studied spectroscopically
a small sample
galaxies polar rings.
to most common
point
of
is that inclined gaseous disks/rings
in lenticular
15.---Age­diagnostic diagram
for stellar populations nuclei
circumnuclear regions galaxies under consideration.
measurements corrected
for emission contamination
as described
in
text. azimuthally averaged measurements radius
galaxies
1
, size
of diminishes
it
travels center. nuclear points supplied
bars, typical accuracy off­nuclear azimuthally averaged indices
8. stellar population models
of Thomas
et
al. (2003)
½Mg=Fe# different plotted dashed
as
ence. Small signs along model curves metallicities +0.67,
+0.35, 0.00, #0.33, #1.35, #2.25,
if
the from
to
left. addition,
the models Worthey (1994) ½Mg=Fe#
¼
same (except oldest model which
¼
17 Gyr instead
plotted solid
to
a very sensitivity
estimates accepted model magnesium­to­iron ratios. metal­
licities Worthey's models +0.50, +0.25, 0.00, #0.22, #0.50, #1.00,
#1.50, #2.00, takes signs
14.---Comparison estimations
of emission­line equiv­
alent widths nuclear spectra galaxies consideration
those (1997). separate emission absorption
multicomponent Gauss analysis (including
[
ii] emission doublet), whereas
subtract pure­absorption template spectra. solid straight shows
relation
y
a dashed
is
the shifted
8
(
y
¼
#
SIL'CHENKO AFANASIEV
2656galaxies, including polar ones, are external origin,
of inclined gaseous structures
is related
to ori­
entation donor galaxy's intrinsic
or orbital spin. How­
ever, results this work
if
inner polar rings accreted another galaxy, above­
mentioned possible external origin spatial and spin
orientation seems
be evident. Indeed,
in seven
galaxies eight our sample some neutral hydrogen have
been detected (only NGC
is detected yet);
it
is
a very high percent lenticular galaxies. example,
normal galaxies
H
i detection 28%
(Wardle Knapp 1986), early­type galaxies with
large­scale polar
it 66% (Huchtmeier 1997). The
presence extended large­scale
H
i disks
in galaxies with
otherwise stellar populations seems
to confirm recent gas
accretion from
a late­type donor. However, galaxies,
NGC 2655 NGC 2787, only detections---we
have
i maps, and orientations
of whole neutral
hydrogen distributions differ strongly orientations
inner ionized For NGC 2655, refer
H
i isophote
in photometric
of Erwin Sparke
(2003):
H
i isophotes strongly elongated, and
intrinsic
H distribution
is round
its nodes
is P:A:
HI 120
# ---let compare this position angle with
inner orientation
# circumnuclear
4
00 kinematic major
of
# (Table For
NGC 2787, there several detailed studies
example, Shostak (1987) having mapped distribution and
kinematics neutral hydrogen this galaxy had
reported roundish outer ring clearly rotates with
kinematical major axis 140
#
# ---let compare with
inner kinematical major
#
#
:
5
lanes orientation #40
# (Erwin 2003). We have
i compare inner outer distributions and
rotations galaxies,
at these cases
permit
us some possible mechanisms inner gas
polar formation.
If inner polar ring outer
neutral hydrogen these galaxies common origin,
must admit when drifting
to centers, gas
changes spin orientation
by almost
#
. all,
yes, under what conditions?
have already mentioned
in
x
1 three­dimensional hy­
drodynamical/gravitational simulations stellar gaseous disks
Friedli Benz (1993). They have found counter­
rotating when drifting
to center, passes strongly
inclined orbits vertical instability effect inner
Lindblad resonance region forms
a stable inclined gaseous
disk, more exactly
a ring, because does reach
very nucleus being stable orbits; Friedli Benz (1995)
because
of counterrotating accumulation this
inclined ring
a formation burst
in nucleus does not
occur. necessary process acting
is
a global
triaxial potential. Among galaxies only NGC
2787,
a formal morphology classification SB0; besides
other galaxies have
a ``B'' (``barred'')
in
LEDA,
as argue
in
x NGC 2768 probably
triaxial bulge. From remaining three, only NGC 2911
Jungwiert
et (1997) certainly stated absence
2732 4111 seen almost edge­on
search for
a difficult these galaxies. However, some
signatures
a boxy bulge usually treated bar
viewed edge­on reported latter galaxy Souza
Anjos (1987) and tticke, Dettmar, Pohlen
(2000). may conclude sufficient condition
pushing inclined orbits---namely, triaxial poten­
tial---is perhaps fulfilled
in most galaxies. NGC 2911,
which certainly unbarred, only case where
inner polar ring
is formed
as
a result minor merger because
have detected some stars related polar ring. However,
even
if most galaxies sample barred, there
problem with another sufficient condition
to make mech­
anism Friedli Benz (1993) work---that
in outer disk
gas counterrotates the stars. the bulk galaxies
under consideration, have
to this condition.
However, NGC 2787, where rotation
mapped Shostak (1987), senses rotation outer
and outer stars (Erwin 2003) coincide.
addition, result Shane Krumm (1983) NGC
2655, ``east side outer ring] approaching''
valid, galaxy also outer corotates stellar disk.
mechanism Friedli Benz (1993) cannot applied
directly least these two galaxies, suppose ex­
ternal origin
of However, the possibility loss
bulge/bar counterrotating stars remains still valid.
second way external supply polar
rings inner and have been acquired
during different accretion events. Almost galaxies
sample located very dense environments: NGC
2655, 2732, 2768, 2911, and 3414 brightest (central)
members
of galaxy groups (Giuricin 2000), NGC
4111 NGC 4233 belong galaxy clusters, Ursa Major
Virgo, respectively. Only NGC 2787---our galaxy,
which information
is available---seems isolated;
however, just galaxy has highest ratio
relate the dense environment effect basing more
extended S0's statistics (Sil'chenko 2002b) that
evidence past group existence around NGC 2787.
In dense
environments seems quite probable that more than
cretion event occur during the Hubble time, the spins
accreting aggregates different initial
orientations. NGC 2655, where circumnuclear stellar
population very young,
T Gyr, there gaseous
subsystems with different orientations because very
central confined plane
of galaxy.
principle, simultaneous existence rather young nuclear
stellar population and circumnuclear plane
is consistent idea Friedli
& Benz (1993) nu­
clear formation bursts effectively fueled only
corotating
in the main planes---only gas
reach center. Then, NGC 2655, identify least
three independent, asynchronous accretion events:
suggest the oldest them formed
a
in
radius range
of
4
00
, the which spiraled
to
center plane fueled recent nuclear star
formation burst, last, recent event pro­
vided extended
i plane orientation inter­
mediate between two preceding ones. However, even after
three satellite accretion events NGC remains
a galaxy, although rather early type, inside
dense environment galaxy successfully avoided major
merger events. presence chemically distinct nuclei
almost other galaxies under consideration implies that
whereas inner polar currently rather stable,
many gigayears ago another violent inflow, probably
confined main galactic disk,
to place
to supply
material those ancient nuclear formation bursts that
formed magnesium­enhanced cores. Let note
in
galaxies with chemically distinct nuclei nuclear Mg/Fe
INNER POLAR RINGS 2657
5, 2004

ratios higher off­nuclear ones. means
clear formation bursts having produced chemically
distinct cores, probably star formation events
nuclei these galaxies, were very brief.
One more remark about stability inner polar
rings.
If accumulates one two main planes
of
a
triaxial structure---that perpendicular the long
or
perpendicular
to short ellipsoid---its rotation
orbits would stable. However, some weak accretion
observed centers our galaxies: Table
can that despite absence
of powerful active nuclei
sample, almost
all galaxies have pointlike nonthermal
sources the nuclei, either radio X­ray. these sources
evidently fueled, there must
be weak radial
flow. interplay rotational and radial motions
areas
of inner polar rings explain some devia­
tions P.A. from P.A. P.A. Table
4.
thank Vlasyuk, Dodonov, and Moiseev
supporting MPFS observations
6 telescope,
and especially Moiseev obtaining images
NGC 2732 with SCORPIO/BTA.
6
m telescope
is
operated under financial support
of Science Ministry
Russia (registration number 01­43). We grateful
Programme Committee
of telescope allocating
observational time. During analysis, used
Lyon­Meudon Extragalactic Database (LEDA) supplied
LEDA team CRAL­Observatoire Lyon (France)
NASA IPAC Extragalactic Database, operated
Propulsion Laboratory, California Institute
of Technology
under contract with National Aeronautics Space
ministration. The work partially based data taken
from the Archive UK Astronomy Data Centre
observations made with NASA Hubble Space
Telescope, obtained from archive Space Tele­
scope Science Institute. STScI operated the Association
Universities Research
in Astronomy, Inc., under
NASA contract NAS5­26555. study young nuclei
lenticular galaxies
is supported Russian Foundation
Basic Research (grant 01­02­16167) Federal
Scientific­Technical Program---contract from Science
Ministry Russia 40.022.1.1.1101.
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