3 Results

The set of Figs. 2 presents for each object in J and K'-bands:

• the 2D image;
• the 1D profiles of surface brightness, ellipticity, and position angle, as a function of the semi-major axis length;
• the J-K' colour map;
• the differential profiles of surface brightness ( $\mu _{J}-\mu _{K'}$), ellipticity ( e_J-e_K'), and position angle (PA_J-PA_K').

In addition, when available, HST NICMOS images are also shown in Figs. 2.

Figure 2: For each of the fifteen galaxies, five (or six) panels are shown: Top left. Radial profiles of surface brightness $\mu$, ellipticity e, and position angle PA. J-band is on the left, K'-band on the right. Note the square root scale. Top right. J and K' grey-scale images with contours superimposed. The spacing is 0.4 mag. North is up, East on the left. Bottom left. J-K' radial profile. Bottom right. HST NICMOS F160W frame (when available) and J-K' colour map

Figure 2: continued

Figure 2: continued

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Figure 2: continued

We hereafter describe the outstanding features and structural parameters of each galaxy, as they have been inferred from Figs. 2, HST images and from the literature. This presentation is not exhaustive; only the characteristics important in the context of this paper are emphasized. All quoted value of the structural parameters refer to the K'-band unless otherwise specified. These parameters are summarized in Table 3 for galaxies with embedded structures. All linear distances have been computed assuming $H_{0}\!=\!75\,{\rm km\,s}^{-1}\,{\rm Mpc}^{-1}$.

3.1 ESO374-G032 (Gpair, STB, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.66$kpc)

The morphology of this galaxy shows evidence of recent or ongoing interaction (mainly a large tidal tail and a disturbed central feature). From the original IR frames, ESO374-G032 shows at least two bright components within the central region separated by around 4 $\hbox{$^{\prime\prime}$ }$ ( $\approx\! 2.6\,$kpc). This complex central structure, also appearing in the visible frame of Kazès et al. (1990), may be a late stage merger. This central feature results in a bar-like contour map and ellipticity profiles. But it is interesting to note that the PA does not show any plateau in the region of this bar. Indeed, it decreases almost linearly from the centre up to $\approx\! 17\hbox{$^{\prime\prime}$ }$. This characteristic could be the signature of the strong interaction, the bar being strongly triaxial and perhaps not coplanar.

3.2 ESO264-G036 (SBb, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.45$kpc)

This is a single-barred object. The well-defined primary bar ends at $\approx\!18\hbox{$^{\prime\prime}$ }$ where a slight twist is observed due to the start of the spiral arms. In the inner region ( $a \leq 2.5\hbox{$^{\prime\prime}$ }$), the $\mu _{J}-\mu _{K'}$ profile steeply decreases from $\approx\! 1.5$ mag $\hbox{$^{\prime\prime}$ }^{-2}$ at the center to $\approx\!1.1$ mag $\hbox{$^{\prime\prime}$ }^{-2}$. The e_J-e_K' profile is roughly constant at $\approx\!0.03$, while the PA_J-PA_K'profile increases from about $-10^{\circ}$ to $\approx\! 5^{\circ}$. For $a \geq 2.5\hbox{$^{\prime\prime}$ }$, the $\mu _{J}-\mu _{K'}$ profile slowly increases again up to $\approx\!1.4$ mag $\hbox{$^{\prime\prime}$ }^{-2}$. This feature corresponds to two red and elongated features, probably star-forming region, close to the bar ends.

3.3 NGC3393 (SBab, STB/Sy2, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.23$kpc)

We confirm previous observations by Jungwiert et al. (1997) and Alonso-Herrero et al. (1998) that this is a double-barred galaxy. In close agreement with these authors, the primary bar is oriented at PA $_{\rm p} \!\approx\! 159^{\circ}$, whereas the trailing secondary bar has PA $_{\rm s} \!\approx\! 145^{\circ}$.

Differential profiles and colour plate show unusual structures: surprisingly, the secondary bar is more prominent on J profiles than on K' ones, leading to a small bump in the e_J-e_K' profile. The $\mu _{J}-\mu _{K'}$ profile presents an artificial negative gradient in the inner region due to the seeing departure from the two IR bands; this gradient must be an artefact because field stars also have a central blue dip in the J-K' colour frame. The same features are reproduced for other objects, when the seeing is artificially degraded in one of the two bands. In Sect. 3.2.2, we use J and K-frames from Alonso-Herrero et al. (1998) to avoid this problem.

3.4 ESO215-G031 (SBb, STB, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.17$kpc)

This SBb starburst galaxy can be considered as the prototype of nearly aligned double-barred systems: the ellipticity profile clearly shows two bumps along which the position angle is nearly constant in both bands. Those bars also tend to reduce the slope of the $\mu_{J}$ and $\mu_{K'}$ profiles along each bar. One of the most striking feature of this object is that the two bars are close to be aligned, $\rm PA_p \!\approx\! 147^\circ$ whereas $\rm PA_s \!\approx\! 153^\circ$, leading to $\theta_{12} \!\approx\! 6^{\circ}$. The ellipticity between those bars declines close to zero at $a \!\approx\! 9\hbox{$^{\prime\prime}$ }$, where the PA variation reveals the presence of a nuclear ring. It is observable on the J-K' image as well. As this galaxy has both inner and outer rings Buta (1995), this is a three-ringed galaxy.

Three distinct regions of redder J-K' colour ($\approx$1.3 mag $\hbox{$^{\prime\prime}$ }^{-2}$) are visible on this structure. Two "hotspots'' or "twin-peaks'' are on the ring and are symmetric with respect to the center, the third one being at the galaxy nucleus. The $\mu _{J}-\mu _{K'}$ profile is nearly constant at 1.1 mag $\hbox{$^{\prime\prime}$ }^{-2}$ along the secondary bar and at 1 mag $\hbox{$^{\prime\prime}$ }^{-2}$ beyond. The e_J-e_K' profile shows a slight negative gradient along the secondary bar, and is close to zero elsewhere.

3.5 ESO320-G030 (SABa, STB, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.21$kpc)

The visual aspect, confirmed by the profile examination, leads us to classify this galaxy as a new double-barred one. The primary bar has a PA $_{\rm p} \!\approx\!142^{\circ}$, different from the PA $_{\rm disc}=121^{\circ}$ (see Table 1), so that this objet should be classified as an SB rather than SAB. This bar also presents two regions of slightly higher surface brightness at its ends. The secondary bar has its outermost isophotes twisted, a nearly constant ellipticity, and PA $_{\rm s} \!\approx\! 107^{\circ}$ (i.e. $\theta_{12} \!\approx\!35^{\circ}$).

An extended central structure, clearly visible on the J-K' colour map, is aligned with the primary bar. This might be a nuclear ring or disc. Nested at the center of this feature, a region of redder colour ( $\!\approx\! 1.4$ mag $\hbox{$^{\prime\prime}$ }^{-2}$) likely corresponds to the secondary bar, but the angular resolution is too poor to reveal unambiguously the bar morphology. The $\mu _{J}-\mu _{K'}$ profile decreases from $\!\approx\! 1.4$ mag $\hbox{$^{\prime\prime}$ }^{-2}$ to reach a constant value ( $\!\approx\!0.9$) beyond $a \approx 9\hbox{$^{\prime\prime}$ }$. The e_J-e_K' and PA_J-PA_K' profiles are roughly zero throughout the galaxy, except for the inner region where they amount to $\!\approx\! 0.04$ and $\!\approx\! 10^{\circ}$respectively.

3.6 ESO443-G017 (SB0/a, STB, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.19$kpc)

This galaxy presents a primary bar with PA $_{\rm p} \!\approx\! 12^{\circ}$that is twisted near its ends as the spiral arms begin to affect the ellipse fitting. The small bump in ellipticity and the constant PA $_{\rm s} \!\approx\! 31^\circ$ suggest the presence of a weak secondary bar. This secondary bar is more pronounced in K' profiles than in Jones, resulting in a e_J-e_K' excess in the central region; it is also visible on the J-K' colour map. However, the disc inclination and PA (Table 1) prevent any reliable detection from being made. A high inclination angle make it difficult to distinguish between a bar and a projected triaxial structure having the same PA as the disc. The projected angle between both bars would be $\theta_{12} \!\approx\! -19^{\circ}$. The $\mu _{J}-\mu _{K'}$ profile is nearly constant ( $\!\approx\! 1.3$ mag $\hbox{$^{\prime\prime}$ }^{-2}$) along the secondary bar, and then decreases down to a constant value of $\approx 1$ mag $\hbox{$^{\prime\prime}$ }^{-2}$ at larger distances.

3.7 NGC4903 (SBc, Sy2, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.31$kpc)

A very strong ( $e^{\rm max} \approx 0.7$) and quite long ( $a_{\rm p} \approx 21\,\hbox{$^{\prime\prime}$ }$) primary bar is visible. It is surrounded by a weakly barred component whose extent and surface brightness might suggest a lens nature. The central part of this galaxy seems to be relatively featureless, even if the very center shows a constant ellipticity ( $e \approx 0.1$) accompanied by a PA variation, in contrast with the profile behaviour at larger radii. This is reinforced by the $\mu _{J}-\mu _{K'}$ gradient observed in the same region, which is also visible on the J-K' frame. But this region needs a higher angular resolution to be reliably probed.

   

Table 3: Non-deprojected morphological parameters in the K'-band for galaxies with embedded structures

Galaxies	Type	1st component			2nd component			Ratios
		a1	$e_1^{\rm max}$	PA1	a2	$e_2^{\rm max}$	PA2	$\beta_{12}$	$\theta_{12}$	$\gamma_{12}$
		$[\hbox{$^{\prime\prime}$ }]$		$[^{\circ}]$	$[\hbox{$^{\prime\prime}$ }]$		$[^{\circ}]$		$[^{\circ}]$
NGC3393	B+B	19.7	0.44	159	3.5	0.12	145	5.6	-14	2.4
ESO215-G031	B+B	$\!\approx\! 47$	0.63	147	9.5	0.48	153	$\!\approx\!4.9$	6	1.7
ESO320-G030	B+B	$\!\approx\! 37$	0.64	142	5.2	0.32	107	$\!\approx\!7.1$	35	2.1
ESO443-G017	B+B	14.7	0.48	12	5.5	0.28	31	2.7	-19	1.5
ESO323-G077	B+T	17.5	0.25	56	7.7	0.18	156	2.3	100	1.2
ESO508-G005	B+dB?	30.9	0.53	161	3.6	0.10	35	8.6	-54	1.8
NGC5135	B+nS	46.1	0.63	127	-	-	-	-	-	-
NGC6221	T+B	$\!\approx\!29$	0.53	116	5.7	0.29	5	$\!\approx\!5.1$	-69	3.0

$\approx$ $\leftrightarrow$ eye-based estimation.
X+Y $\leftrightarrow$ X qualifies large-scale structures (1st component), whereas Y stands for small scale ones (2nd component);
B$\,=\,$Barred isophotes, T$\,=\,$Twisted isophotes, nS$\,=\,$nuclear Spiral-like feature, dB$\,=\,$"dissolved Bar''.

3.8 NGC4941 (SABab, Sy2, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.08$kpc)

The $\mu$, e, and PA profiles all indicate the presence of a nuclear bar, without any large-scale bar. The nuclear bar, clearly visible on the NICMOS F160W frame, is characterized by $\rm PA_{s} \!\approx\! 180^{\circ}$, $e_{\rm s}^{\rm max} \!\approx\! 0.32$, and $a_{\rm s} \!\approx\! 5\,\hbox{$^{\prime\prime}$ }$. NGC7702, which also harbour a nuclear bar ( $e_{\rm s}^{\rm max} \!\approx\! 0.43$, $a_{\rm s} \!\approx\! 10\,\hbox{$^{\prime\prime}$ }$, see Paper I), is visually very close to this galaxy; even the orientation of the bar relative to the disc major axis are similar ( $\vert{\rm PA}_{\rm s}-{\rm PA}_{\rm disc}\vert\approx 20^{\circ}$).

The $\mu _{J}-\mu _{K'}$ profile shows a slight decrease along the nuclear bar and is nearly constant afterwards ( $\!\approx\! 1$ mag $\hbox{$^{\prime\prime}$ }^{-2}$).

3.9 NGC4939 (SAbc, Sy2, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.19$kpc)

The regular decrease of the surface brightness, the roughly constant PA at the same angle as the disc ( $\!\approx\! 10^{\circ}$, see Table 1), and the high inclination angle of this galaxy, all indicate that the ellipticity behaviour should mostly be due to projection effects of a disc plus spiral arms (see e.g. Jungwiert et al. 1997 for examples of projection effects). Thus, this galaxy really seems unbarred, even if the central isophotes enhanced in the NICMOS F160W frame, have a boxy shape.

Most striking is the big difference in ellipticity between J and K' band in the central region ( $\mu_{J}-\mu_{K'} \!\leq\! 0.1$ at the center).

3.10 ESO323-G077 (SB0, STB/Sy1, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.29$kpc)

The relatively weak primary bar is oriented at PA $_{\rm p} \!\approx\! 56^\circ$, and ends near $\approx\! 17.5\,\hbox{$^{\prime\prime}$ }$. The inner prominent structure has a moderate ellipticity, and presents a monotonous PA increase from about 150$^{\circ}$ to 175$^{\circ}$, close to the PA value of the disc (Table 1). These isophote twists certainly indicate the presence of a triaxial bulge. The $\mu _{J}-\mu _{K'}$ profile reaches the reddest colour of our sample at the center of the galaxy ( $\!\approx\! 2.2$ mag $\hbox{$^{\prime\prime}$ }^{-2}$). This extremely red, roughly axisymmetric region, is striking on the J-K' map. Moreover all the differential profiles show strong departure from zero toward the center.

3.11 ESO508-G005 (SB0/a, Sy2, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.19$kpc)

This galaxy harbours a clear primary bar with PA $_{\rm p} \!\approx\! 161^\circ$. The central region ( $a\!\leq\!4\,\hbox{$^{\prime\prime}$ }$) presents a nearly constant and low ellipticity ( $e \approx 0.1$) with a twisted PA around 35$^{\circ}$. These profiles clearly suggest the presence of a nuclear component (as to be compared with the profile of a "pure'' single-barred galaxy like e.g. ESO264-G036). Moreover, this region is also slightly redder: the $\mu _{J}-\mu _{K'}$ profile displays a central plateau at $\!\approx\! 1.1$ mag $\hbox{$^{\prime\prime}$ }^{-2}$, whereas beyond another plateau has $\!\approx\!0.9$ mag $\hbox{$^{\prime\prime}$ }^{-2}$. A similar feature is observed in the double-barred galaxy ESO215-G031 and ESO443-G017!

As PA$_{\rm s}$ fairly differs from PA $_{\rm disc}$, the central morphology is unlikely to result from the projection of a triaxial bulge. Therefore, an appealing and plausible possibility might be that this component is simply the "remnant'' of a secondary bar, or a secondary bar in the process of dissolution (for details see e.g. Friedli 1999). This hypothesis might for instance be checked via stellar and gaseous kinematics to detect fossil signatures of previous potential asymmetries.

3.12 NGC5135 (SBab, STB/Sy2, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.27$kpc)

The most striking feature of this galaxy is its very special center. In view of the $\mu$, e, and PA profiles, one could think of a three-component object, i.e. both primary (PA $\approx 130^\circ$) and secondary (PA $\approx 140^\circ$) bars separated by a triaxial bulge. However, the visual inspection of J, K' frames instead suggests the presence of a nuclear bi-symmetric spiral structure nested in the primary bar. This inner component is highlighted on the J-K' colour map. It is also visible on the WFPC2 image Malkan et al. (1998 as a dusty and patchy flocculent nuclear spiral. The peculiar nature of this nucleus is strengthened by the highly disturbed differential profiles, which reveal the very unusual differences between J and K'-bands.

Even on high resolution HST frames, it is very difficult to know if these spiral arms really start from a nuclear bar. Indeed, due to the high amounts of dust and the intense star forming regions, ellipse fits are problematical even on NICMOS F160W images.

3.13 NGC5643 (SABc, Sy2, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.08$kpc)

Both NIR frames show abnormal structures in the southern region; reflection on a misaligned filter could give rise to such ghosts (none of these structures are visible on the DSS optical frame). So the colour gradient in the J-K' colour frame is an artefact. However, as the central region of interest is less affected, ellipse fitting was performed on this area. Following its NIR morphology, we suggest to classify this galaxy as an SB one rather than SAB. The $\mu _{J}-\mu _{K'}$ profile is nearly constant $\approx\! 1$ mag $\hbox{$^{\prime\prime}$ }^{-2}$ and presents a slight increase near the center ( $a\!\leq\!1.1\,\hbox{$^{\prime\prime}$ }$).

3.14 NGC 6221 (SBbc pec, Sy2, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.10$kpc)

This galaxy may be in weak interaction with NGC6215 Koribalski (1996a), and with two low-surface brightness galaxies Koribalski (1996b). The classification of this galaxy is somewhat controversial since de Vaucouleurs et al. (1991) classify it as a barred spiral, SBc, whereas Sandage & Tammann (1981) classify it as an ordinary spiral, Sbc. This uncertainty probably comes from the dual nature of this object. Because it exhibits properties of both early and late-type, Vega Beltrán et al. (1998) state that NGC6221 is an intermediate snapshot of a spiral evolving from early to late-type. Nevertheless near-IR profiles revealed a clear nuclear bar (already mentioned in Forbes & Norris 1998) nested in a twisted structure. N-body simulations Pfenniger (2000) have shown that such an object could evolve toward a double-barred system as the shape of the large-scale twisted isophotes becoming more and more bar-like after several dynamical time-scale.

Tsvetanov & Petrosian (1995) have detected 173 H II regions throughout the galaxy. The more intensive ones are mostly located along the primary bar, near the center and along the spiral arms, and are also traced by the big redder structures visible on our J-K' colour plate. Thus even if the IRAS indicator does not lead us to classify this object as starburst ( $\log(S_{60}/S_{100}) \!\approx\! -0.36$), it experiences active star formation.

Vega Beltrán et al. (1998) also detect a ring-like structure of ionized gas with a radius of about 9 $\hbox{$^{\prime\prime}$ }$. Moreover this ring is related to the presence of an inner Lindblad resonance (ILR) of the primary bar. At this radius the ellipticity effectively reaches a minimum, but no ring is clearly visible on the J-K' colour plate.

This galaxy has a $\mu _{J}-\mu _{K'}$ profile similar to that of previous objects like ESO443-G017.

3.15 NGC6300 (SBb, Sy2, $1\hbox{$^{\prime\prime}$ }\!\approx\!0.08$kpc)

Already outlined by Mulchaey et al. (1997), NGC6300 harbors a primary bar ( $a_{\rm p} \approx 50\,\hbox{$^{\prime\prime}$ }$), whereas we could not confirm the presence of the secondary bar they also suspected. Although this object experiences active star formation like NGC6221, no strong starburst seems to be active near the central region, except for intense nuclear emission (Crocker et al. 1996 report that H II regions are mostly concentrated in the inner ring at $a\!\approx\! 42\hbox{$^{\prime\prime}$ }$). The $\mu _{J}-\mu _{K'}$ profile is roughly constant outside the center and is steeply increasing inside .