2 Observations and data analysis

2.1 The sample

The sample is composed of radio galaxies in the redshift range $0.01\leq z \leq0.12$ extracted from two complete surveys of radio sources.

The first one is the all sky survey of radio sources with radio flux at 2.7 GHz greater than 2 Jy by Wall & Peacock (1985; hereafter WP). From this survey we extracted all objects, in the above redshift range, classified as radio galaxies (see also Tadhunter et al. 1993) at declination $\delta<10^\circ$.

The second list is the Ekers et al. (1989; hereafter EK) catalogue of radio galaxies with flux at 2.7 GHz greater than 0.25 Jy and m_b<17.0, in the declination zone $-40^\circ<\delta<-17^\circ$. All objects classified as E or S0 in the above redshift range were included in our list. Basic data for the 50 objects presented in this paper are summarized in Table 1. Columns 1 and 2 give for each object IAU and other names, Col. 3 gives the subsample, Cols. 4 and 5 the equatorial coordinates (equinox 2000.0), and Col. 6 the redshift. Columns 7 and 8 report the K-correction in the R band and the galactic extinction in the V band. We derived the galactic extinction interpolating the data for galactic hydrogen column density given by Stark et al. (1992) and assuming A_V/E_B-V=R=3.2 and $E_{B-V}=N_{\rm H}/5.1 \ 10^{21}$ (Knapp & Kerr 1974). In Cols. 9 and 10 we give the radio classification and reference.

Based on the radio morphology, sources were divided into FRI and FRII radio classes following the Fanaroff & Riley scheme (Fanaroff & Riley 1974). Most sources in the WP sample were imaged by Morganti et al. (1993) with the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA), while VLA radio images are available for most objects in the EK sample. Objects with transitional properties or with unclear classification are marked as I/II, while a U marks the only unresolved source 1323-271. For IC 4374 (labeled with a question mark) we were not able to find a radio image, thus we include it in the FRI class because its radio luminosity at 178 MHz is below $2\ 10^{25}$ Watt/Hz, the dividing luminosity between the two classes.

2.2 Observations

Observations were secured in five different observing runs. Beside three galaxies (0307-305, 0332-391 and 1928-340) included here, the results of the imaging in B and R bands obtained with the ESO-2.2 m telescope during runs 1 and 2 (Table 2) have been reported in Paper I. Data presented here were obtained in three more observing runs (run 3, 4, 5) with either the ESO-Danish 1.5 m telescope or the Nordic Optical Telescope (NOT). The journal of observations is given in Table 3, where for each object we report the run of observation, the total integration time, the atmospheric seeing expressed by the full width half maximum (FWHM) of stellar images, and the sky surface brightness, together with its estimated 1$\sigma$ uncertainty. The galaxy total apparent R band magnitude (corrected for galactic extinction) computed by extrapolating to infinity the surface brightness profile is also given. This value does not include the K-correction.

For most objects a short ($\sim$ 2 min) and a long exposure (Table 3) were obtained, so we also have an unsaturated image of the nuclear region. In a few cases, the presence of bright stars in the field forced us to take several short exposures, subsequently combined to form a final, deep image. Photometric conditions were generally good during the observations, as confirmed by repeated observations of photometric standard stars selected from the Landolt (1992) list. Comparison of the photometric zero point for different nights indicates an average internal photometric accuracy of 5-10%. This, combined with the small uncertainty on the sky surface brightness (1-2%), gives a global internal photometric accuracy of the order of 10%. The atmospheric seeing was generally around 1 arcsec, and the CCD pixel size (Table 2) were always sufficiently small to ensure proper sampling of the telescope point spread function (PSF).

 

Table 3: Journal of observations

IAU name	run	exp	FWHM	$\mu_{\rm sky}$	$\sigma_{\rm sky}$	$m_{\rm tot}$
		(sec)	(arcsec)	(mag/arcsec2)	(mag/arcsec2)	(mag)
0255+058	5	900	1.02	20.7	0.019	12.75
0257-398	3	1200	1.33	21.2	0.005	14.38
0307-305	2	900	1.40	20.5	0.007	14.70
0312-343	3	1200	1.29	21.3	0.006	14.01
0325+023	5	900	1.21	20.8	0.012	12.70
0332-391	2	1200	1.70	20.7	0.007	14.06
0344-345	3	1500	1.44	21.1	0.004	14.70
0427-539	3	600	1.13	21.2	0.005	12.69
0430+052	3	1200	1.33	20.8	0.004	13.01
0434-225	3	1200	1.33	21.3	0.007	13.33
0446-206	3	1200	1.16	21.1	0.005	14.81
0452-190	3	1200	1.35	21.4	0.009	13.00
0453-206	3	600	1.37	21.4	0.007	12.57
0511-305	3	1800	1.39	21.2	0.004	14.66
0533-377	3	1800	1.49	21.4	0.009	14.57
0546-329	3	1200	1.27	21.3	0.006	12.34
0548-317	3	900	1.50	20.8	0.010	13.42
0620-526	3	600	1.64	20.8	0.017	12.53
0625-354	3	900	1.25	20.0	0.009	13.11
0625-536	3	1200	1.21	20.9	0.006	12.39
0634-205	3	1800	1.31	20.9	0.008	13.90
0712-349	3	1200	1.30	20.2	0.010	12.98
0718-340	3	1200	1.25	20.9	0.008	12.15
0806-103	3	600	1.20	20.8	0.007	15.20
0915-118	3	600	1.35	20.1	0.009	13.23
0940-304	3	600	1.20	20.7	0.013	13.12
0945+076	3	1800	1.23	20.4	0.010	15.19
1002-320	3	1200	1.17	19.9	0.008	14.52
1043-290	3	300	1.17	20.5	0.012	13.22
1053-282	3	1800	1.13	19.7	0.006	13.86
1056-360	3	1800	1.19	19.6	0.006	14.64
1107-372	3	300	1.2	19.5	0.005	9.53
1123-351	3	510	1.21	20.3	0.010	11.92
1251-122	3	600	1.25	20.1	0.009	10.63
1251-289	3	1800	1.17	18.9	0.004	12.41
1257-253	3	1200	1.2	19.8	0.006	13.92
1258-321	3	1200	1.10	19.8	0.015	10.71
1318-434	3	600	1.20	19.9	0.012	9.98
1323-271	3	1800	1.10	19.5	0.013	13.14
1333-337	3	600	1.20	19.9	0.006	9.97
1344-241	3	1200	1.25	20.4	0.010	12.37
1354-251	3	600	1.25	20.4	0.007	13.36
1400-337	4	1200	1.25	20.9	0.010	9.72
1404-267	4	1200	1.25	20.8	0.012	11.71
1637-771	4	1200	1.55	20.6	0.008	13.54
1717-009	4	1200	1.15	20.7	0.010	13.87
1733-565	4	900	1.25	20.2	0.008	15.22
1928-340	2	1200	1.20	20.2	0.018	14.31
1949+023	5	1200	0.72	20.7	0.010	14.11
2221-023	5	1200	0.67	20.9	0.012	14.46

2.3 Data reduction and surface photometry

Data reduction is extensively described in Paper I. Here we simply remind the reader that the IRAF-ccdred package was used for the basic reduction (bias subtraction, image trimming, flat fielding, cosmic rays, etc.). The dark current turned out to be insignificant and was neglected. After flat fielding, images were characterized by a quite regular sky background, well fitted by a first order polynomial.

Final images are shown in Fig. 1, where it is seen that selected sources cover an area of hundreds of arc-seconds square, ideal for two-dimensional isophotal analysis, and can be traced down to a surface brightness of $\mu_R\sim 25$ mag/arcsec². It is also evident that these radio galaxies are often observed in highly crowded regions, with stars and/or nearby galaxies projected on-top. Sky subtraction and isophotal analysis (drawing, cleaning and fitting) was performed using the AIAP package (Fasano 1990), which due to its high degree of interactivity, is particularly suitable in analyzing the morphology of galaxies embedded in such high density regions.

The problem of obtaining reliable surface photometry of dumbbell systems was faced by adopting the two-galaxy fitting strategy outlined in Paper I, which allows us to fully separate the two galaxies. Contour plots for all dumbbell systems, together with those of the two members are shown in Fig. 10.

From this analysis we derived photometric and structural parameters (surface brightness, ellipticity, position angle and Fourier coefficients) as a function of the equivalent radius $r = a\times(1-\epsilon)^{1/2}$ where a is the semimajor axis and $\epsilon$ is the ellipticity of the ellipse fitting a given isophote. Isophotes can not be fitted in the innermost few arcsec of the galaxy because of the small number of pixels involved. To cope with this limitation, we extracted an azimuthally averaged radial profile, centered on the center of the first useful isophote. If the nucleus was saturated, the short exposure was used. The agreement between this average radial profile and that obtained from isophote fitting was always excellent in the common region, thus the two profiles were joined smoothly to fully model the core and the outer region of the galaxies. In the following analysis we consider this combined profile as the final luminosity profile.

After fitting of the isophotes with ellipses, photometric and morphological profiles have been obtained according to the procedure described in Paper I. For each galaxy, the luminosity radial profile, the major axis position angle (defined from North to East), the ellipticity, and c4 coefficient profiles as a function of the semi-major axis are shown in Fig. 12. The Fourier coefficient c4 measures the deviation of the isophotes from the best fitting ellipse. A positive values indicate the isophote is excessively elongated along the major axis, i.e., it is similar to a disk, while a negative c4 means the isophote is boxy.

The residual background variations inside each frame were used to derive, according to Fasano & Bonoli (1990), proper errors for morphological and photometric parameters.

For the dumbbell system in Fig. 3 we show only the luminosity profile of the radio source.