EDP Sciences
Free Access
Issue
A&A
Volume 526, February 2011
Article Number A43
Number of page(s) 32
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361/200913243
Published online 20 December 2010

Online material

Appendix A: Contour maps and profiles of the Sy galaxies

We present contour maps and profiles of the SB, CI, ϵ, and PA of the Sy galaxies in Fig. A.1.

thumbnail Fig. A.1

Calibrated contour maps and profiles of the Sy galaxies, ordered by right ascension. Upper panels: contour maps. North is up and east to the left. The galaxy names and passbands are specified in the upper left; the numbers in the upper right denote the start SB, the end SB, and the SB step (fixed to 0.5) in units of mag   arcsec-2. Lower panels: profiles of SB, CI, ϵ, and PA. The CI profiles shown are B   –   IC (solid) and V   –   IC (dashed); for Ark 120 B   –   RC (dash-dotted) is shown. For the rest of the profiles the solid, long-dashed, short-dashed, and dotted line is for the B-, V-, RC-, and IC-band, respectively. For Mrk 352, Mrk 771, and Mrk 279 the HST profiles are also plotted (squares; their SB profiles are not calibrated).

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Appendix B: Comments on Sy sample galaxies

thumbnail Fig. B.1

Mrk 335 IC model-subtracted residual image. The extended feature is clearly visible.

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thumbnail Fig. B.2

Mrk 352 RC unsharp mask-divided residual image. The nuclear ring can be discerned.

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thumbnail Fig. B.3

Mrk 352 HST WFPC2 F606W 2D model-subtracted residual image. The bar encircled by a ring can be traced.

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We discuss the Sy sample galaxies concerning features found or particularized by this study and cases where the influence of some features on the profiles is essential for the true structural parameters estimation via decomposition.

When discussing the contour maps and profiles, reference to Fig. A.1 goes without saying. Furthermore, CI and residual images/maps, contour maps, structure maps, and 2D model-subtracted residual images (Figs. B.1B.29) visualize the individual comments; dashed/dotted lines correspond to ellipticity maxima/minima. In all figures north (N) is up, east (E) to the left; the rest of the directions have been abbreviated as follows: south (S), west (W), northeast (NE), northwest (NW), southeast (SE), southwest (SW). In the CI images black is blue, white is red. Concerning the residual images, white are the excess structures.

B.1. Mrk 335

There is an extended feature at PA   =    −43° with IC peak SB away from the nucleus (Fig. B.1). The B   –   V, V   –   RC, and RC   –   IC CIs of this feature, estimated on the model-subtracted residual images by means of aperture photometry, are 1ṃ48, 0ṃ75, and 0ṃ89, respectively (correction for Galactic extinction was applied after Schlegel et al. 1998). The feature is redshifted by about 280 km   s-1 and shows a steep Balmer decrement (Fricke et al. 1983). The authors discussed ejection or merging and found the latter unlikely. MacKenty (1990) proposed an edge-on background galaxy as another interpretation. In our view, given the undisturbed appearance of the galaxy, a companion or a merging satellite at an early stage, seen through Mrk 335, is a plausible hypothesis. No radio counterpart of the feature has been observed (e.g., Kukula et al. 1995).

B.2. III Zw 2 (III Zw 2A in NED)

The contour map and the model-subtracted residual map reveal an elongation to the SE, which is a merging galaxy (separation of about 7″; Surace et al. 2001), connected through a tidal bridge with III Zw 2, as can be seen in the residual images of Veilleux et al. (2006), and an arm-like extension to the N, which is a tidal counterarm with knots of star formation (see also Surace et al. 2001). The tidal arm and the merging satellite produce an SB bump, accompanied by blue CI dips and an ellipticity maximum at a continuously changing PA in the region a ≈ 5″–10″.

B.3. Mrk 348

The galaxy has a distorted outer spiral structure (e.g., Pogge & Eskridge 1993) due to interaction with its close companion, which shows a CI gradient (Antón et al. 2002).

The ellipticity increase and the SB bump beyond a ≈ 45″ are related to the diffuse stretched outer spiral structure. The inner spiral structure leads to a continuous change of the PA. The weak SB bump, visible in B, and the blue B   –   IC dip at a ≈ 5″ are produced by a blue nuclear ring, more pronounced to the S (Antón et al. 2002).

B.4. I Zw 1

The galaxy has asymmetric knotty spiral arms (the NW one being more pronounced) that may be of tidal origin (Surace & Sanders 2000; Canalizo & Stockton 2001). They produce an SB bump, CI dips, and an ellipticity maximum at a continuously increasing PA in the region a ≈ 7″–13″.

thumbnail Fig. B.4

Mrk 573 B   –   IC map. The contours range from 1.2 to 1.95 with a step of 0.05   mag   arcsec-2. Overplotted are the B model contours corresponding to the first two ellipticity maxima and the minima following them. The first ellipticity maximum is related to the ionization cones.

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thumbnail Fig. B.5

Mrk 573 RC residual image, composite of an unsharp mask-divided-subtracted one, so that there could be traced the arcs and the outer ring. Overplotted are the model contours corresponding to the V ellipticity maxima.

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thumbnail Fig. B.6

Mrk 590 HST ACS/HRC F550M structure map. The dust lanes can be traced.

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B.5. Mrk 352

There is evidence of a nuclear bar around a = 2″: the ellipticity profile shows a peak, accompanied by a plateau on the PA profile; however, there is no obvious SB bump. Moreover, the unsharp masked residual reveals a nuclear ring (Fig. B.2). To further verify our findings, we processed archival HST WFPC213F606W data. Subtraction of a fitted 2D bulge-disk model (the nucleus was masked out) reveals a θ-shaped residual (Fig. B.3), most probably due to a nuclear bar surrounded by a ring. In the region around a = 2″ the ellipticity and PA profiles show a similar behaviour like ours and, in addition, the SB profile reveals a weak bump; we used the HST profiles to derive the bar parameters. Furthermore, the SB profile has a weak bump, accompanied by ellipticity peaks at a ≈ 4″, which we associate with the ring. Besides this, there is no significant dust (Deo et al. 2006) that could disturb the corresponding isophotes.

B.6. Mrk 573

The B   –   IC map (Fig. B.4) exhibits two blue regions corresponding to the ionization cones (Ferruit et al. 1999). They result in a blue dip on the CI profiles and BV ellipticity maximum at a ≈ 3″. The V maximum was misinterpreted as evidence of a secondary bar14 by Afanasiev et al. (1998). The second ellipticity maximum (at a ≈ 9″) corresponds to a bar. The B   –   IC map also reveals a couple of arcs (labelled SE3 and NW3 by Ferruit et al. 1999), which appears as a broken ring in the unsharp masked residual image (Fig. B.5).

The SB profiles in the region 25″−40″ are affected by an outer ring (Pogge & De Robertis 1995), clearly outlined in Fig. B.5. The profiles show signs for another bar at a ≈ 21″ as already proposed by Laine et al. (2002). After a 2D elliptical ring model subtraction, the ellipticity maximum decreases and the weak SB bump vanishes, which keeps us from considering this galaxy triple barred (see also Erwin 2004).

thumbnail Fig. B.7

Mrk 595 V unsharp mask-divided residual map. Overplotted are the V model contours corresponding to the two ellipticity peaks. There can be traced the oval/lens, together with the spiral arm stubs.

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thumbnail Fig. B.8

Mrk 595 V   –   IC map. The contour levels range from 1 to 1.4 with a step of 0.025   mag   arcsec-2; overplotted are the V model contours corresponding to the two ellipticity peaks. The mapped region roughly reflects the [O iii] emission.

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thumbnail Fig. B.9

Ark 120 B residual image, composite of two unsharp mask-subtracted residual images so that there could be traced the inner knotty ring and the two faint arcs running to the N.

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B.7. Mrk 590

Pogge & Martini (2002) reported a nuclear bar, based on HST WFPC2 images. In their structure map, a ring-like structure around the bar could also be seen, best traced to the NE. We processed archival HST ACS/HRC15F550M data and created a structure map, which reveals several dust lanes. A couple of them appear as straight dust lanes along bar leading edges (although the bar signatures are not very evident, Fig. B.6) and could be traced down to about 70 pc () in radius.

B.8. Mrk 595

The profiles and contour map suggest a bar-like structure, which is most probably an oval/lens, given its small deprojected ellipticity of 0.1316. Weak spiral arm stubs can be seen in the unsharp masked residual map (Fig. B.7). The V   –   IC map (Fig. B.8) reveals a blue region to the NW, which roughly reflects the [O iii] emission (see also Mulchaey et al. 1996).

The oval/lens produces an ellipticity peak and an SB bump at an almost constant PA in the region a ≈ 4″−8″. The BV ellipticity peak, accompanied by a weak B SB bump and blue CI dips around a = 11″, is caused by the spiral arm stubs. The [O iii] emission results in enhanced ellipticity in V and in blue V   –   IC dips in the regions of the two ellipticity peaks (Fig. B.8).

B.9. 3C 120

The contour map reveals strongly disturbed isophotes due to underlying features (Soubeyran et al. 1989; Hjorth et al. 1995), which affect the SB profiles.

thumbnail Fig. B.10

Mrk 376 RC residual image, composite of an unsharp mask-divided-subtracted one. The bent bar, the clumpy ring around it, and the two spiral arms, forming a weak outer pseudo-ring, are clearly outlined.

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thumbnail Fig. B.11

Mrk 376 V   –   IC image; the CI coding ranges from 1.1 to 1.6   mag   arcsec-2. The clumpy blue ring can be traced.

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thumbnail Fig. B.12

NGC 3227 B contour map. The model levels, corresponding to the ellipticity maximum and minimum around a  =  20″, are plotted over the relevant galaxy levels. The dust imparts a disturbed appearance to the isophotes.

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B.10. Ark 120

The unsharp masked residual image (Fig. B.9) reveals a blue knotty ring (a  ×  b  ≈  9″  ×  8″) and a couple of arcs extending to the N on either side of the nucleus, the W one being more pronounced. The ring produces an SB bump and a blue dip on the B   –   RC profile.

B.11. Mrk 376

The unsharp masked residual image (Fig. B.10) reveals a bent bar. It is encircled by a ring (a  ×  b  ≈  5″  ×  3″) with knots of star formation that are outstanding in the V   –   IC image (Fig. B.11). The two spiral arms get noticeably not as bright and form a weak outer pseudo-ring (a  ×  b  ≈  14″  ×  9″). The bar results in an ellipticity maximum around a = 4″ (the less pronounced ellipticity maximum in B is due to seeing change), accompanied by an SB bump at an almost constant PA. The inner ring produces an SB bump (best expressed in B), which merges with the bar bump, and a CI dip. The spiral structure results in weak SB bumps further out. Note that “spiral arms or a bar-like structure” in the NIR were hinted at by Hughes et al. (1993).

B.12. Mrk 79

The galaxy is asymmetric: the NW spiral arm is truncated and the NE bar side is diffuse. The outer isophotes have a rectangular shape (see also Wehinger & Wyckoff 1977). The bar produces an SB bump, together with an ellipticity maximum in the region a ≈ 6″−17″; the ellipticity is highest in B due to the partial fitting of the spiral arm beginnings. The wavelength-dependent ellipticity bump next to the maximum, accompanied by an SB bump and a blue CI dip, is produced by the inner part of the spiral structure. The behaviour of the profiles17 beyond a   =   24″, is related to the outer spiral structure.

B.13. Mrk 382

Mrk 382 has a bar with a ring (a  ×  b ≈ 9″  ×  7″) around it. The spiral structure forms an outer pseudo-ring (a  ×  b  ≈  17″  ×  12″). The ellipticity maximum, accompanied by an SB bump around a = 7″ results from the bar; the second ellipticity maximum and the corresponding SB bump are due to the spiral structure.

B.14. NGC 3227

The ellipticity profile shows a broad maximum in the region a ≈ 25″–85″, double-peaked in B, accompanied by SB bumps, best expressed in B. The behaviour of the profiles around the inner part of the ellipticity maximum is dominated by the bar, and in the region of the outer part of the ellipticity maximum, is due to the spiral arm beginnings, which result in blue B   –   IC dips and a slight PA shift, best expressed in B.

When analysing a decomposition residual image, González Delgado & Pérez (1997) argued for an N-S stellar bar of a ≈ 1.6   kpc (≈ 21″, assumed distance to the galaxy 15.6 Mpc). Furthermore, based on isophotal analysis, Gadotti & de Souza (2006) reported a bar of a = 1.9   kpc (≈22″, assumed distance to the galaxy 17.6 Mpc). In this region – more precisely, around a = 17″ – the profiles show complex behaviour: the ellipticity profile has a wavelength-dependent maximum, accompanied by a constant (but also wavelength-dependent) PA. At variance with the above authors, we attribute this to dust absorption: the dust location is such that the absorption by it causes an ellipticity increase and a PA shift, relative to the galaxy PA, when moving to shorter wavelengths (compare Figs. B.12 and B.13). In the NIR the PA does not show any shift relative to the galaxy PA, and the ellipticity profile does not have a maximum in this region (see Fig. 2 of Mulchaey et al. 1997).

thumbnail Fig. B.13

NGC 3227 IC contour map. The model levels, corresponding to the ellipticity maximum and minimum around a = 20″, are plotted over the relevant galaxy levels. Compare with Fig. B.12.

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thumbnail Fig. B.14

NGC 3516 RC residual image, composite of an unsharp mask-divided-subtracted one, so that the bar and rings can be traced.

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thumbnail Fig. B.15

Mrk 766 V unsharp mask-subtracted residual image. Overplotted is the V   –   IC map (the levels range from 0.9 to 1.15 with a step of 0.05   mag   arcsec-2; solid) and the V ellipticity maximum. Note the outer pseudo-ring, the blue region oriented NW–SE, and the blue protrusion to the NE.

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thumbnail Fig. B.16

Mrk 771 IC model-subtracted residual map. The contours relevant to the c4 coefficient maximum (a =    4″; dash-double-dotted) and to the ellipticity maximum are overplotted. Note the cross-shaped structure, the disky isophote associated with it, and the features extending on either bar side.

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thumbnail Fig. B.17

Mrk 771 IC unsharp mask-subtracted residual image. The asymmetric spiral structure is clearly outlined.

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thumbnail Fig. B.18

Mrk 279 RC structure map. The oval/lens, together with the other features discussed in text could be traced.

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thumbnail Fig. B.19

Mrk 279 RC unsharp mask-subtracted residual map with the model contour corresponding to the ellipticity maximum and the ones bracketing it (a ≈ 8″,   16″; dash-dotted) overplotted. The ellipticity maximum is related to the two straight features.

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thumbnail Fig. B.20

Mrk 279 B  −  IC image. The CI coding ranges from 1.7 to 2.3   mag   arcsec-2. The outer galaxy parts are blue and asymmetric, and the companion gets bluer towards Mrk 279.

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thumbnail Fig. B.21

Ark 479 V unsharp mask-subtracted residual image. The bar and spiral structure can be traced.

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B.15. NGC 3516

The unsharp masked residual image (Fig. B.14) is suggestive of an incomplete inner ring around the bar. The presence of some structures at the bar ends was mentioned by Knapen et al. (2002).

B.16. NGC 4051

The dust lane to the S of the nucleus (Deo et al. 2006) causes the B ellipticity peak at a  ≈ 10″. The bar and spiral arms together result in a broad ellipticity maximum, accompanied by SB bumps in the region a  ≈ 25″–110″.

B.17. NGC 4151

The behaviour of the profiles in the inner 15″ is most probably related to an inner disk on a similar scale (e.g., Simkin 1975; Bosma 1981; Gadotti 2008), an extended narrow-line region (Pérez et al. 1989; Asif et al. 1998), and dust arcs (e.g., Ulrich 2000).

B.18. Mrk 766

The higher V ellipticity maximum in the region of the bar is related to the [O iii] emission, extended along the NW–SE direction (Fig. B.15, see also Mulchaey et al. 1996).

B.19. Mrk 771

The cross-shaped structure in the model-subtracted residual map (Fig. B.16), accompanied by disky isophotes (positive fourth-order Fourier cosine coefficient c4; we define c4 after Milvang-Jensen & Jørgensen 1999) is due to the combined influence of the bulge and bar. There is a chain of blue knots near the SW bar end (see Fig. B.16) that has been associated with a small merging companion (Hutchings & Neff 1992; Hutchings et al. 1994) or with the bar itself, given the similar fainter feature near the opposite bar end (Surace et al. 2001). Similar structures have been observed in Mrk 279. The unsharp masked residual image (Fig. B.17) reveals a weak asymmetric spiral structure forming a nearly complete pseudo-ring.

In the region of the bar, the ellipticity profile has a broad maximum at a roughly constant PA; however, the expected SB bump is not present as the outer bar parts remain unfitted (Fig. B.16). The SB bump around a = 6″, accompanied by a V   –   IC dip and a peak, superposed on the ellipticity maximum, is related to the features on either side of the bar. To estimate the bar parameters, we extracted archival HST WFPC2 F606W profiles, on which the ellipticity peaks due to the bar and the features discussed are detached. The innermost variations in the profiles are artifacts from the guide hole of (Hutchings & Neff 1992).

thumbnail Fig. B.22

Mrk 506 RC structure map. The rings, together with the spiral arms, are clearly outlined.

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thumbnail Fig. B.23

3C 382 RC model-subtracted residual map. Three filaments are outstanding. The object 16 ″ to the W, cleaned from the images, is shown here for illustration.

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thumbnail Fig. B.24

NGC 6814 RC unsharp mask-divided residual image. The model contour, corresponding to the ellipticity maximum, is overplotted. The bar and the spiral structure can be traced.

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B.20. NGC 4593

The bar causes a broad ellipticity maximum around a = 47″, accompanied by an SB bump. The blue V   –   IC dip, together with an SB bump overlapping with the bar SB bump and an ellipticity peak superposed on the bar ellipticity maximum around a = 65″, is related to an inner ring.

B.21. Mrk 279

The direct images reveal an outer ring displaced to the NW compared to the inner galaxy parts (the annular appearance of the outer galaxy parts has already been noticed by Adams 1977) and a tail-like feature to the S. Around a = 5″ there is an SB bump, accompanied by almost constant ellipticity and PA, and the ellipticity profile, extracted from the archival HST WFPC2 F814W images, has a peak. In the corresponding region, the structure map (Fig. B.18) reveals a bar-like structure (its parameters were estimated using the HST profiles), which is most probably an oval/lens, given the small deprojected ellipticity of 0.13. The bar hypothesis has already been discussed (Knapen et al. 2000; Pogge & Martini 2002; Scott et al. 2004). Furthermore, there are two straight features on either side of the oval/lens (similar to those in Mrk 771) and some more compact structures about 15″ NE and 9″ SE of the nucleus (see Fig. B.19). The NE structure appears blue and elongated in the HST images, and the SE one, which is actually two objects that are most probably projected, is red. Furthermore, the straight features (hinted at by Adams 1977) and the tail-like one are blue; as a whole, the outer galaxy parts appear blue and asymmetric (Fig. B.20). The disturbed morphology of Mrk 279 could be a result of interaction with the companion, which is bluer and more extended toward it. The unsharp masked residual image reveals spiral arm stubs in the companion, suggesting SA0/a pec morphology.

The wavelength-dependent ellipticity maximum at a ≈ 13″ is related to the straight features. The ring produces an SB bump, accompanied by blue CI dips around a = 17″. The spiral dust lanes, best traced at a ≈ 5″–8″ in the HST images (see e.g., Pogge & Martini 2002), produce the red CI bump around a = 6″.

thumbnail Fig. B.25

NGC 7469 B   –   IC image. The CI coding ranges from 1.6 to 2.7   mag   arcsec-2. Overplotted are the model contours corresponding to the two IC ellipticity peaks. The pseudo-rings and the dust can be traced.

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thumbnail Fig. B.26

NGC 7603 V model-subtracted residual image. There can be traced a complex of loop-like features and a filament with two emission-line galaxies overposed (encircled).

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thumbnail Fig. B.27

NGC 7603 V   –   IC image. The CI coding ranges from 1.15 to 1.7   mag   arcsec-2. Note the red dust lanes and the blue loop-like features.

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B.22. NGC 5548

The galaxy has shells and tidal tails that are suggestive of a merger event (Schweizer & Seitzer 1988; Neff et al. 1990; Tyson et al. 1998). The shells and the curved tail result in SB bumps and in ellipticity and PA peaks.

B.23. Ark 479

The ellipticity profile shows a maximum around a = 6″ accompanied by a weak SB bump and an almost constant PA, which corresponds to a bar. The unsharp masked residual image (Fig. B.21) reveals the bar and spiral structure. The latter causes wavelength dependence of the ellipticity maximum and produces a weak SB bump (best expressed in V) further out.

thumbnail Fig. B.28

Mrk 541 RC residual image, composite of an unsharp mask-divided-subtracted one. The broken inner ring and the knotty outer ring are clearly outlined.

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thumbnail Fig. B.29

Mrk 541 V   –   IC image. The CI coding ranges from 0.9 to 1.5   mag   arcsec-2.

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B.24. Mrk 506

The structure map (Fig. B.22) reveals a blue inner ring (a  ×  b  ≈  9″  ×  6″), noticed already by Adams (1977), and a couple of faint spiral arms, emerging out of it and reaching a faint outer ring (a  ×  b  ≈ 16″  ×  13″). It is useful to note that Su & Simkin (1980) included Mrk 506 in the group of double-ringed galaxies. The inner ring produces a B   –   IC dip and an SB bump, and the weak B bump following the latter is due to the spiral arms.

Although Mrk 506 is classified as weakly barred (RC3), the behaviour of the profiles does not indicate a bar. Furthermore, after a 2D elliptical ring model subtraction, the SB bump around a = 9″ practically disappears.

B.25. 3C 382

Three filaments can be discerned in the model-subtracted residual map (Fig. B.23). The NE and E filaments are oriented toward a barred spiral galaxy about to the NE. According to Roche & Eales (2000), the two galaxies are interacting and the blue object 16″ to the W (Fig. B.23) might be a gas-rich starburst dwarf galaxy in the process of merging into 3C 382. In our view, this object is most probably projected. It has a stellar-like appearance in archival HST WFPC2 images; subtraction of Tiny Tim generated PSF (Krist 1995) left no significant residual structure.

The SW filament could also be of tidal origin. The ellipticity dip around a = 11″ is associated with the NE filament. The filaments result in weak SB bumps.

B.26. NGC 6814

A weak bar can be traced in the unsharp masked residual image (Fig. B.24). Its signature on the profiles, however, is masked by the spiral structure, that produces SB bumps, best pronounced in B, blue CI dips, and a wavelength-dependent ellipticity maximum in the region a ≈ 10″–40″. To estimate the bar parameters, we extracted J profiles (using Two Micron All Sky Survey images), on which the ellipticity peaks due to the bar and the spiral arm beginnings are detached.

B.27. Mrk 1513

The SB bump around a = 14″ is produced by the outer pseudo-ring.

B.28. Ark 564

The bar results in an ellipticity maximum, accompanied by an SB bump around a = 8″. The partial fitting of the spiral arm beginnings by the model causes wavelength dependence of the ellipticity maximum, a blue B   –   IC dip, and an SB bump, overlapping with the bar bump and largest in B. The spiral structure forms a blue pseudo-ring (a  ×  b  ≈ 16″  ×  12″), which produces an SB bump and a B   –   IC dip.

B.29. NGC 7469

The ellipticity profile shows a maximum around a = 14″, accompanied by an SB bump, and an almost constant PA. The behaviour of the profiles there is not typical – in the inner part it is dominated by an inner pseudo-ring (a  ×  b  ≈ 13″  ×  7″), and in the region of the outer part it is due to a bar-like structure (Fig. B.25). This is best illustrated in IC by a double-peaked ellipticity maximum and a corresponding weak double structure of the SB bump. Given the small deprojected ellipticity of 0.12, the bar-like structure is most probably an oval/lens. Márquez & Moles (1994) suggested the bump is due to a lens but based mainly on the fact that they could not find a reasonable fit by a bar. The wavelength dependence of the ellipticity maximum is caused by the inner pseudo-ring and the spiral structure. The variations in the PA profile are related to the spiral structure.

B.30. Mrk 315

The inner 7″ of the profiles are influenced by underlying features. Ciroi et al. (2005) associated them with a dwarf galaxy

remnant and star formation regions; a faint spiral structure could be traced in their residual images.

B.31. NGC 7603

NGC 7603 and the galaxy about 1′ to the SE are an example of an anomalous redshift association (Arp 1971). NGC 7603 is disturbed and shows evidence of tidal interaction (see López-Corredoira & Gutiérrez 2004, and references therein).

There are a number of loop-like features (Fig. B.26), which appear blue in the V   –   IC image (Fig. B.27). They result in an SB bump, accompanied by a blue V   –   IC dip and a weak ellipticity peak at a ≈ 21″.

B.32. Mrk 541

The unsharp masked residual image (Fig. B.28) unveils an inner ring (a  ×  b  ≈ 7″  ×  5″), broken roughly along the galaxy minor axis and a knotty outer ring (a  ×  b  ≈  20″  ×  13″), more pronounced to the W and displaced to the N with respect to the nucleus. Both rings appear blue in the V   –   IC image (Fig. B.29). The outer ring was noted already by Adams (1977), and Su & Simkin (1980) included Mrk 541 in the group of double-ringed galaxies. The rings produce SB bumps, accompanied by blue dips on the CI profile.


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