We include into this section all galaxies which have, or at least are suspected to have, more than one triaxial structure. We do not strictly distinguish between double bars and bars with embedded triaxial bulges since this difference is rather elusive. Usually, we speak about double bars; only in cases when the inner ellipticity maximum is low (after deprojection) and/or not clearly separated from the outer one we use the latter term. The classification of some galaxies as double-barred is speculative, because either they are too inclined or the central resolution is low.
NGC 613 (SBbc/Seyfert, pc, ):
This Seyfert galaxy is known to possess, inside the large-scale bar, an optical nuclear spiral. BC93 give semi-major axes of the feature . We identify short nuclear spiral arms also in the near-IR and suggest, on the basis of both the ellipse fitting and the inspection of the grey-scale image, that they have an associated nuclear bar ( at a=5.3''). If our interpretation is correct, then NGC 613 is a new example of a double-barred system. The primary bar peaks () outside our image.
NGC 1079 (RSAB0/a, pc, ):
The highest peak in ellipticity ( at ) is related to the large-scale bar, however the shape of the profile can be deformed by the presence of spiral arms at the end of the bar. There is a secondary maximum ( at a=17'') that we attribute to the triaxiality of the bulge.
NGC 1353 (SBb, pc, ):
The galaxy inclination is rather high and the interpretation therefore uncertain: we suggest that the innermost ellipticity peak is associated with a nuclear bar along which the PA varies as a result of projection effects. The large-scale bar is reflected by the PA plateau around a=14'' and a corresponding small bump in the ellipticity. The outermost ellipticity maximum is related to large-scale spiral arms. The deprojection, although done, is considered to be unreliable.
NGC 1365 (SBb/Seyfert 1, pc, ):
The galaxy has an IR-bright Seyfert nucleus and, as in the case of NGC 613, a nuclear spiral, best seen as prominent dust lanes in optical images (e.g. Teuben et al. 1986). NGC 1365 is also classified as a starburst galaxy (e.g. Telesco et al. 1993), with the star-forming activity concentrated in circumnuclear "hot-spots''.
The morphology of the nuclear region is complex and patchy also in our H image, indicating that the emission of old red stars is probably strongly contaminated by the light of new red giants and supergiants formed in the starburst. The nuclear spiral is well recognized and we identify a nuclear bar embedded in it: the peak in the ellipticity ( at a=8.3) is related to that bar while the adjacent minimum in the PA is related to the nuclear spiral. The nuclear bar is roughly parallel () to the elliptical distribution of circumnuclear molecular gas mapped by Sandqvist et al. (1995). Neither the spiral nor the bar are smooth, unlike in NGC 613.
NGC 1398 (R'SBab, pc, ):
The disk is dominated by a well defined large-scale bar reaching (0.37) at a=36'' after which it passes into an outer ring. The inner isophotes (a<20'', ) are not aligned with the primary bar () and are slightly twisted (by between 5 and 12''). A small bump in profiles near a=14'' was found also by W95 but they were reluctant to interpret it. We consider it is related to the triaxiality of the bulge; its signature is seen also in deprojected profiles (). Note that the inner isophote twist almost disappears after deprojection: the PA is constant (within ) along the whole 60''-profile.
NGC 1433 (R'SBab, pc, ):
The double barred structure of the galaxy was already reported by Buta (1986) and W95 in BVRI bands. We find, in JHK bands, the length of the secondary bar to be 5.6, 5.4 and 6.2''. For comparison with W95 we measured also and 12.8'' (W95 give 11.5'' in filter I). The primary bar exceeds in length our frame, so that its ellipticity is still increasing at the last point of the profile. The PAs of bars are 32 and (with the nuclear bar leading), in good agreement with W95 (30 and ).
NGC 1512 (SBa, pc, ):
The image is dominated by a large-scale bar showing isophotal twist () exterior to (noticed by E96 on the blue plate). A low ellipticity maximum and the associated change of the PA at can be indicative of a distinct component, probably a triaxial bulge. This interpretation is however uncertain because of high inclination (note a partial similarity with Fig. 2 (click here) showing a projection of a double barred system).
NGC 1808 (RSABa/HII, pc, ):
NGC 1808 is a nearby starburst galaxy (e.g. Telesco 1993) with many star forming knots inside 1 kpc. It is also suspected to possess a hidden Seyfert nucleus (e.g. Véron-Cetty & Véron 1985).
On the H image the nuclear region looks smooth, unlike in optical. This is consistent with Tacconi-Garman et al. (1996) who claim that the near-IR emission from the nucleus of this galaxy is dominated by old stars with only a small () contribution from young red giants and supergiants born in the starburst. We interpret the peak in the eccentricity and the associated PA plateau at as a manifestation of a nuclear bar (its presence was recently deduced also by Kotilainen et al. (1996) on the basis of JHK contour plots). We do not attempt to give parameters of the large-scale bar since the galaxy has a peculiar morphology (possibly due to the interaction with NGC 1792) and our image is spatially rather small. Phillips (1993) classifies the galaxy as barred on the basis of the distribution of HII regions and Saikia et al. (1990) report an HI bar 22 kpc long. Therefore we classify NGC 1808 as being double-barred.
NGC 2217 (RSB0+, pc, ):
We identify this low-inclination galaxy as a new double-barred system: the two maxima in ellipticity ( at a=7.8'' and at a=37'' occur on the approximate plateaus of the PA ( and for the secondary and primary bar, respectively).
NGC 2935 (R'SABb, pc, ):
The outer ellipticity peak corresponds to the large-scale bar ( at a=25''). We interpret the secondary maximum, still perceptible after deprojection, as being related to another triaxial component, probably the bulge (the shape of the profile in the transition region between the two peaks can be partly deformed by the presence of a badly masked star near the major axis of the inner component at , however the inspection of the grey-scale image confirms that the inner misaligned structure really exists). The smooth twist of the barred isophotes (already noticed by E96 on blue plates) is explainable by projection effects. After deprojecting, the PA is two-fold with two approximate plateaus.
NGC 3368 (SABab, pc, ):
One can see three ellipticity maxima (, 0.30 and 0.43) accompanied by three plateaus in the PA profile. The third maximum is controversial since it is close to the locus where spiral arms start and our frame ends at the same time. The illusion of the triple-barred system disappears after deprojection (): it seems plausible that the galaxy is double-barred with the two bars roughly aligned. However, as I is rather high for the deprojection to be unambiguous, we do not exclude that three triaxial components coexist.
NGC 3393 (R'SBa/Sey 2, pc, ):
Inside the large-scale bar ( at a=13.3), there is an isophote twist of between a=3'' and 4.4''. We speculate that it could result from the existence of a small secondary bar, since there is a local maximum of ellipticity near a=2'', while the PA has a plateau there. The proximity of that region to the center makes the double-bar classification uncertain; higher resolution is needed to confirm the discovery.
NGC 4984 (RSAB0+, pc, ):
The ellipticity peak () around a=4'' is associated with a short plateau in the PA ( between 2.9 and 4.1''). Since the peak is even better seen after deprojection (), we believe that it indicates the presence of a short bar. The outer ellipticity maximum ( at a=30'') is related to the primary bar. Both bars are intrinsically nearly parallel provided the deprojection is correct (cf. Fig. 3 (click here)).
NGC 5101 (RSB0/a, pc, ):
The isophotes inside the large-scale bar ( at a=50'') are strongly twisted (). Such a twist is not explainable by mere projection effects in view of rather low galaxy inclination. Either there is an intrinsic gradual twist or a nuclear bar as would suggest the ellipticity maximum and the PA plateau at a<3'': however the proximity of this feature to the center as well as its low ellipticity ( at a=2'') make this hypothesis very speculative.
NGC 5566 (SBab, pc, I=79.5):
In spite of the high inclination of the galaxy, we interpret the profiles in terms of a double barred structure with the higher maximum in ellipticity ( at ) corresponding to the nuclear bar. The large-scale bar has, due to projection, only a low ellipticity peak ( at ) and a short PA dip. We think that the deprojected profiles are not meaningful - because - and show them only as illustration of how weak the deprojection procedure is for such high inclinations (e.g. note the constancy of the deprojected ellipticity at a high value near the center).
It is interesting to compare this galaxy with NGC 3166 since both are highly inclined and their morphology is apparently similar on undeprojected images: at first sight, both seem to show a double barred structure with the components roughly perpendicular. Nevertheless, in the light of Sect. 3 and Figs. 1 (click here) and 3 (click here), we classify NGC 3166 as having only a large-scale bar while NGC 5566 is claimed to have two bars. To grasp the difference, note that in the (undeprojected) ellipticity profile of NGC 3166, there is no local maximum interior to that of the large bar; rather, the ellipticity monotonically climbs towards the center. This is characteristic of projection effects: the behaviour is qualitatively similar to Fig. 1 (click here)b in which the bar is projected along its minor axis as is the case of NGC 3166 (in comparison, keep in mind that the profile of NGC 3166 reflects also the disk - which adds the change of ellipticity and PA rightwards from the bar ellipticity maximum - and that the inclinations are different - which changes the relative height of the peak). On the other hand, NGC 5566 shows two ellipticity peaks (excluding the outer raising slope related to the disk); ellipticity decreases towards the center. That is why we interpret the structure as double barred: no projection of a single bar with reasonable ellipticity profile (monotonically increasing as suggested by face-on single barred galaxies) can generate a secondary ellipticity peak.
NGC 6782 (RSABa, pc, ):
A double bar structure, discussed already by BC93 and W95, exists, with the primary (, ) and secondary (, ) bars oriented at and , respectively. The deprojection () does not alter this picture: two peaks in ellipticity, along which the PA is roughly constant, still exist.
ESO 437- 67 (R'SBab, pc, ):
This galaxy could be double-barred since two peaks in ellipticity ( at 2.5'' and 0.62 at 31.8'') are associated with approximate plateaus in the PA (139 and ). Nevertheless, this classification is speculative because the inner feature is rather close to the center: higher resolution is desirable to confirm the hypothesis.
NGC 1792 (SAbc, pc, ):
The ellipticity maximum inside 10'' is related to a short nuclear bar ( at 5'') along which no clear twist occurs. Further ellipticity maxima are connected to spiral arms.
NGC 4438 (SA0/a(pec)/Sey 3, ):
This galaxy (Arp 120), possessing a Seyfert nucleus, is interacting with a close companion NGC 4435 in the Virgo cluster Its nuclear regions might be perturbed by infalling gas (e.g. Combes et al. 1988; Kenney et al. 1995). Its inner maximum in ellipticity could reflect either a tidally deformed bulge or a nuclear bar.
NGC 5427 (SAc/Seyfert 2, pc, ):
The ellipticity profile shows four clear maxima, the highest of which (at ) corresponds to the two-arm spiral structure. The two innermost ones ( and 8'') do not correspond to well defined plateaus in PA, however the changes in ellipticity and PA occur at roughly the same places. We agree with W95 that these features are oval structures whose nature remains controversial, which is perhaps connected to the interacting nature of NGC 5427. Nevertheless, we note that after deprojection, the PA is defined much better in the inner region: it is constant up to 6'', i.e. within the first ellipticity peak which could indicate a nuclear bar in this region. This interpretation is tempting also because of the Seyfert nucleus.
In this section, galaxies with gradual twist along their large-scale bars are described. The selection is done on the basis of undeprojected images: some of such twists are likely not to be intrinsic.
NGC 1187 (SBc, pc, ):
The ellipticity grows to its maximum () at a=32'', reflecting the large-scale bar from the tips of which two-arm spiral structure emanates. The PA is roughly constant inside the bar except the innermost region (a=2 - 7'') where a -twist occurs. After the deprojection (), a possibility that the system is double-barred emerges: the PA is essentially two-fold and there is a new maximum in ellipticity at about 3''. In case that the secondary bar really existed, it would be nearly perpendicular to the primary one (). However, we believe that such an appearance is likely to be an artefact of a wrong deprojection (cf. Fig. 1 (click here)) and, in accordance with rules established in Sect. 3, we classify the galaxy only as having a twist.
NGC 1302 (RSB0/a, pc, ):
Between a=3 - 7'' the PA is roughly constant () but then it turns by along the bar whose (0.35) occurs at a=29''. This twist was already noted by W95 who attributed it to the presence of dust lanes since its amplitude depends on the band (BVRI). It is important that we found it also in band H where the dust extinction is much less important.
NGC 1832 (SBbc, pc, ):
The eccentricity of the large-scale bar grows continuously to at a=17'' where a regular two-armed spiral structure starts. There is a twist of amplitude inside the bar. The twist is even more pronounced () after deprojection ().
NGC 2442 (SABbc, pc, ):
The inner isophotes are twisted inside the large-scale bar: between a=3'' and 10''.
NGC 2525 (SBc, pc, ):
The large-scale bar, with maximum ellipticity of 0.69 (at a=22''), has twisted isophotes: . The deprojection () is suspicious: the resulting big twist is probably the consequence of unexact deprojection parameters and noisy image.
NGC 2997 (SABc, pc, ):
The twist of amplitude between a=4'' and 7.3'' can be due to projection effects alone.
NGC 3166 (SAB0/a, pc, ):
Looking at inner contours, one could easily get impression that the galaxy is double-barred, with the bars roughly perpendicular one to another. However, this appearance is probably entirely due to projection effects (note that no ellipticity peak corresponds to the first PA plateau; cf. Fig. 1 (click here) and comments on NGC 5566). After deprojection (), no clear isophote twist is found.
NGC 3637 (RSB0/a, pc, ):
Inside the large-scale bar ( at a=14.6''; ), a strong twist (amplitude in the region a=3''-14.6'') is measured. The resolution in the inner part is not sufficient to say whether a secondary bar exists.
NGC 3673 (SBb, pc, ):
There is a small twist ( between a=3'' and 42'') inside the large-scale bar ( at a=42'')
NGC 3887 (SBbc, pc, ):
Inner isophotes (between a=3'' and 25'') inside the large-scale bar ( at a=33''; ) are twisted by .
NGC 4454 (RSB0/a, pc, ):
There is a strong twist ( between a=3'' and 12'') inside the large-scale bar ( at a=31''; ). The galaxy is only moderately inclined () and the twist almost disappears (reduces to ) after deprojection.
NGC 4612 (SB0+, pc, ):
The isophotes of this lenticular galaxy severely twist () between a=2'' and a=15.7'' where the ellipticity has a maximum (). After deprojection (), the ellipticity has a peak () along which the PA is roughly constant while a small twist () still exists within the innermost 10''. We interpret the profiles as resulting from the presence of a weak bar (we do not feel obvious to classify the galaxy as strongly barred as it is in RC3).
NGC 4665 (SB0/a, pc, ):
There is a small gradual twist along the large-scale bar ( between a=3'' and 42'' where).
NGC 5643 (SABc/Seyfert 2, pc, ):
Despite the low disk inclination, there is a strong twist ( between a=3'' and 30'') inside the large-scale bar. This is interesting, because NGC 5643 belongs to late-type (Sc) galaxies - which are expected not to show a twist (Elmegreen et al. 1996) - and, at the same time, has a Seyfert nucleus.
NGC 5701 (RSB0/a, pc, ):
There is a strong twist ( between a=3'' and 38'') inside the large-scale bar ( at a=38'', ), probably not explainable by projection effects since the galaxy inclination is only 15.
NGC 1255 (SABbc, pc, ):
No evidence for twist is found; the first, rather flat peak in ellipticity ( at a=4.4'') corresponds to the bar () , while the second, more pronounced (at ) is related to a double-armed spiral structure. The profiles are qualitatively similar after deprojection ().
NGC 1640 (SBb, pc, ):
The PA is constant () along the large-scale bar whose ellipticity maximum (0.62) is reached at a=31''.
NGC 1744 (SBd, pc, ):
The galaxy is inclined at and, moreover, our image is noisy: the ellipse fitting is not reliable. No clear evidence for twist is found.
NGC 1784 (SBc, pc, ):
The ellipticity profile shows one maximum ( at a=26'') near the end of the large-scale bar. The PA is well constant (between 91 and ) along the bar.
NGC 2911 (SA0/Seyfert 3, pc, ):
The PA, as well as the ellipticity, are rather flat inside a=12''. The small features further out are most likely due to badly masked stars.
NGC 3346 (SBcd, pc, ):
No twist is found inside the primary bar ( at a=13'').
NGC 4050 (SBab, pc, ):
The PA is roughly constant () along the large-scale bar.
NGC 4106 (SB0+, pc, ):
The PA is remarkably constant () within a=11.5''. The ellipticity has a maximum (0.37) inside that PA plateau (at a=5.3''). The PA grows later on while the ellipticity decreases.
NGC 4212 (SAc, ):
The ellipticity peak near a=29'' is related to spiral arms, not to a bar structure. The inner isophotes, inside 10'', show no clear twist: an oblate bulge is probably sufficient to explain the profiles.
NGC 4267 (SB0-, pc, ):
The PA is constant along the large-scale bar ( at a=18.4'', ) of this low-inclination galaxy.
NGC 4424 (SBa, ):
The galaxy is inclined at . The twist inside the bar ( reached at a=8''; ) does not exceed .
NGC 4501 (SAb/Seyfert 2, pc, ):
The bulge region is characterized by growing ellipticity. However, the constancy of the PA ( interior to a=18'') - as well as the fact that its value corresponds to that of the outer disk - is compatible with a spheroidal shape of the bulge: there is no evidence for a bar or other triaxiality. The change of eccentricity and PA behind a=18'' reflects the presence of spiral arms.
NGC 4519 (SBd, pc, ):
No isophotal twist is found inside the bar region of this late-type galaxy.
NGC 4689 (SAbc, pc, ):
Multiple features in the ellipticity and PA profiles result from flocculent spiral structure. No clear twist occurs in the nuclear region.
NGC 4731 (SBcd, pc, ):
The galaxy is rather inclined and the ellipse fitting is unreliable. No clear twist is found.
NGC 4781 (SBd, pc, ):
No clear twist is found inside the large-scale bar ( at a=6.3'', ). Spiral arms are responsible for features in the profile at larger distances.
NGC 4900 (SBc, pc, ):
The galaxy is seen approximately face-on () and no twist is found inside the large-scale bar ( at a=4.9'', ). Further out, an irregular spiral structure causes changes in the ellipticity and PA profiles.
NGC 4902 (SBb, pc, ):
The PA inside the large-scale bar ( at a=25'') is approximately constant (within ).
NGC 5236 (M 83) (SABc, ):
The nuclear structure of this nearby "hot-spot'' starburst galaxy (e.g. Telesco et al. 1993) is complex also in our JHK images and the ellipse fitting in the central region not too meaningful (it even fails in J). The structure, patchy but dissimilar from optical and mid-IR will be analyzed elsewhere.
NGC 6753 (RSAb, pc, I=29.3):
The ellipticity and PA profiles of this galaxy show several small peaks related probably to the presence of star forming regions and flocculent spiral structure of the outer disk, as W95 have already noted. No clear triaxial feature can be found.
IC 1953 (SBd, pc, ):
The PA is constant inside the large-scale bar ( at a=23'', ).
Galaxies listed below have the inclination higher than . We publish their contour plots and ellipse fitting profiles but do not attempt to interpret them: NGC 1518 (SBdm, pc, ): NGC 2811 (SBa, pc, ), NGC 3384 (SB0-/AGN?, pc, ), NGC 3593 (SA0/a, pc, ), NGC 3885 (SA0/a, pc, ), NGC 4178 (SBdm, ), NGC 4192 (SABab/Seyfert 3, ), NGC 4216 (SABb, ), NGC 4442 (SB0, pc, ), NGC 4461 (SB0+, pc, ), NGC 4503 (SB0-, pc, ), NGC 4546 (SB0-, pc, ), NGC 4684 (SB0+, pc, ), NGC 4694 (SB0/HII, pc, ), NGC 4856 (SB0/a, pc, ), NGC 6810 (SAab, pc, ).