For each galaxy, total B, V, R and I magnitudes were measured from the CCD images. They were determined from apertures chosen interactively to assure that the diaphragm is large enough to contain the whole galaxy but still small enough to limit the magnitude error due to the sky error. Foreground stars within the aperture were removed interactively. Table 4 gives the magnitudes.
and 
obtained in this work were checked against
the magnitudes given in the ESO-LV catalogue. It was found that the
ESO-LV magnitudes are systematically brighter than those measured here.
For the galaxies observed in
photometric conditions, one obtains 
with a scatter of 
and
with a scatter of
. These differences are
in agreement with independent studies. Peletier et al. (1994) found that
their B-magnitudes are 
, and their R-magnitudes
fainter than those in the ESO-LV
catalogue. This result is
difficult to interpret because the agreement of the magnitude differences
indicate a systematic zero-point
offset for the ESO-LV magnitudes. However,
Paturel et al. (1994) compared
magnitudes in the ESO-LV catalogue with those given in the RC3
catalogue (de Vaucouleurs et al. 1991) and did not find any significant zero
point differences between the two catalogues.
CCD magnitudes for the I-filter are available for ESO-LV
463-0200, 351-0180, 351-0250, 412-0210 and
352-0720 (Mathewson & Ford
1996). Comparison with total I-magnitudes obtained in this work
for the galaxies observed in photometric conditions gives
a mean difference of 
with
a scatter
of 
. This shows that there exists a zero-point difference between
the two magnitude systems with the magnitudes obtained in this work being
systematically fainter. The reason for this difference could not
be found.
For the galaxies observed in non-photometric conditions, comparison of
and
with the ESO-LV data and of 
with the data of Mathewson & Ford does
not show any significant deviations from the magnitude differences
obtained for the galaxies measured in photometric conditions. This indicates
that for these galaxies the
errors for integrated magnitudes and surface brightness
due to the weather conditions can be regarded as smaller
than 
.
| ESO-LV | |  | | |  | PA |
| 339-0120 | 14.06 | 13.32 | 12.79 | 12.29 | 0.36 | 3.4 |
| 463-0200 | 13.47 | 13.19 | 12.32 | 11.94 | 0.63 | 158.2 |
| 235-0080 | 13.28 | 12.74 | 12.28 | 11.73 | 0.25 | 131.3 |
| 286-0630 | 14.04 | 13.44 | 12.99 | 12.49 | 0.48 | 46.1 |
| 411-0170 | 15.74 | 14.77 | 14.23 | 13.62 | 0.51 | 69.7 |
| 351-0180 | 15.39 | 14.84 | 14.31 | 13.91 | 0.65 | -3.4 |
| 351-0220 | 15.42 | 14.68 | 14.39 | 13.96 | 0.46 | 162.7 |
| 351-0240 | 16.19 | 15.28 | 14.82 | 14.05 | 0.61 | 142.7 |
| 351-0250 | 15.30 | 14.57 | 14.09 | 13.49 | 0.28 | 126.0 |
| 351-0310 | 15.49 | 14.67 | 14.18 | 13.59 | 0.33 | 166.7 |
| 412-0210 | 15.39 | 14.49 | 13.89 | 13.27 | 0.62 | 38.6 |
| 352-0400 | 15.66 | 14.87 | 14.45 | 13.83 | 0.52 | 187.5 |
| 352-0540 | 15.33 | 14.45 | 13.88 | 13.22 | 0.83 | 126.1 |
| 352-0720 | 15.54 | 14.65 | 14.07 | 13.35 | 0.79 | 173.5 |
Figure 1 (click here) shows surface brightness 
, apparent ellipticity and
position angle PA plotted against the apparent semimajor axis r for the
sample galaxies.
and PA are plotted for the R-filter because
the R-images are those with the highest signal-to-noise ratio and the
ellipticity as well as the position angle profiles are very similar for
different wavelength regions.
Figure 1: Surface brightness , apparent ellipticity
and position angle PA against semimajor axis r.
and PA are taken from the R images. For details see text
For galaxies which are not edge-on, the inner parts of the profiles are dominated by the light distribution of the bulge while the outer parts are dominated by the spiral arms. For galaxies with prominent spiral arms (ESO-LV 339-0120, 235-0080 and 352-0400), apparent ellipticity and position angle vary strongly throughout the galaxy.
For edge-on or nearly edge-on galaxies (ESO-LV 463-0200,
351-0240, 352-0540 and
352-0720), the inner parts of the profiles are dominated by the bulge, while
the outer parts are dominated by the overall shape of the disc.
The apparent ellipticity is small in the center, but throughout
the linear
part of the surface brightness profile,
increases systematically until it reaches a constant value, which is
the true apparent ellipticity of the galaxy disc.
For each galaxy, and PA for 
in the R-filter are taken as a measure for and
PA of the whole galaxy. This
isophote has been chosen because it is well within the disc.
Table 4 gives magnitudes, apparent ellipticity and position angle for each
galaxy. Comparison with the values given in the ESO-LV catalogue shows a
good agreement for almost all sample galaxies. The mean differences are
with a scatter of 0.14 and 
with a scatter of
.
There is, however, one galaxy for which the -value given in the
ESO-LV catalogue
strongly deviates from that obtained from the profile. This is
found for ESO-LV
352-0720, where 
is given in the ESO-LV catalogue.
The galaxy image shows an object with very high ellipticity, so the
value of 0.39 is not representative for
the outer parts of this galaxy. The value of 
found in this work is much more realistic
for the galaxy as a whole.
The surface brightness profiles obtained in
photometric
conditions were compared to those given in the
literature. The ESO-LV catalogue contains low-resolution photographic
surface brightness profiles
in B and R for all sample galaxies.
For B, a mean difference of 
with a scatter of 
was found. For R, the mean difference is 
with a scatter of
. The profiles obtained in this
work are
systematically fainter than the ESO-LV profiles. Most of this deviation is
explained by the magnitude zero-point difference. Part of the deviation is
found in
the outer parts of the profiles, i.e. the profiles obtained in this work are
steeper than those in the ESO-LV catalogue. It is not clear what causes this
deviation. The differences are probably not due to the uncertainty in
the sky subtraction. As a check the images with the fitted
ellipses were subtracted from the original image. For none of the sample
galaxies, any significant
parts of the galaxies are found to be remaining after subtraction.
I-profiles of four of the sample galaxies observed in photometric
conditions (ESO-LV 463-0200, 351-0250, 412-0210
and 352-0720) are also found
in Mathewson & Ford (1996). The mean surface brightness difference is
with a scatter of 
. As for the B and R filters, this is
larger than expected from
the magnitude zero-point difference, but is in a better
agreement than the
- and 
-profiles with the ESO-LV catalogue.
In order to determine
scalelength 
and central surface brightness 
of the disc,
an exponential law was fitted to the surface
brightness profiles of each sample galaxy.
Since the linear parts of the
profiles are the ones dominated by the disc, these parts
were used for the fit.
Bulge parameters were not fitted because the angular diameters of the bulges
are so small that they are strongly influenced
by seeing.
| ESO-LV no. |  |  |  |  |  |
 |  |  | Range |
| 339-0120 | 23.8 | 21.4 | 21.2 | 20.7 | 21.75 | 20.92 | 20.36 | 19.83 | 17-24 |
| 463-0200 | 22.1 | 19.2 | 18.6 | 16.9 | 20.83 | 20.36 | 19.43 | 18.91 | 10-49 |
| 235-0080 | 16.4 | 17.3 | 17.5 | 17.9 | 19.04 | 18.85 | 18.50 | 18.13 | 16-26 |
| 286-0630 | - | 17.2 | 17.2 | 17.1 | - | 18.61 | 18.16 | 17.66 | 17-31 |
| 411-0170 | 17.2 | 15.7 | 15.3 | 15.1 | 21.88 | 20.52 | 19.82 | 19.16 | 17-12 |
| 351-0180 | 12.8 | 11.0 | 10.5 | 18.4 | 21.77 | 20.96 | 20.29 | 19.62 | 10-24 |
| 351-0220 | 16.8 | 16.8 | 16.4 | 16.1 | 21.02 | 20.29 | 19.83 | 19.38 | 17-21 |
| 351-0240 | 18.2 | 13.8 | 12.7 | 11.3 | 22.51 | 21.34 | 20.71 | 19.86 | 19-21 |
| 351-0250 | 16.5 | 17.0 | 16.9 | 16.9 | 21.04 | 20.52 | 20.02 | 19.49 | 19-21 |
| 351-0310 | 16.5 | 15.7 | 15.7 | 15.4 | 21.05 | 20.01 | 19.53 | 18.87 | 12-19 |
| 412-0210 | 17.8 | 17.8 | 17.5 | 16.8 | 21.06 | 20.25 | 19.59 | 18.85 | 10-31 |
| 352-0400 | - | 14.0 | 13.8 | 13.8 | - | 19.79 | 18.87 | 18.28 | 10-17 |
| 352-0540 | 24.5 | 18.4 | 16.0 | 13.9 | 21.89 | 20.72 | 19.84 | 19.05 | 10-31 |
| 352-0720 | 19.3 | 15.8 | 15.0 | 11.1 | 21.96 | 20.86 | 20.21 | 19.16 | 19-21 |
Table 5 shows the results obtained for and . The
-profiles for ESO-LV 286-0630 and ESO-LV 352-0400
do not show any linear parts, so no fits were made for them.
In order
to obtain a scalelength which is not influenced by the inclination angle
of the galaxy,
is measured along the apparent semimajor axis. The errors
for
and are obtained by comparing the values for different sub-parts
of the linear parts of the
profiles. ESO-LV 463-0200 and 351-0180 could be observed twice. The
sets of images were taken under different seeing conditions. The difference
of and found between these two sets are also used to determine
the error. The errors obtained for and are similar for each
galaxy
and filter. Typical values are 
and 
.
It has been found by many authors that the surface brightness profiles of
spiral galaxies often show
deviations from an exponential law, which sometimes makes the definition of
the linear
part difficult. As can be seen in Fig. 1 (click here), such deviations
are present in the galaxies studied here. The error of 
for is mainly due to these deviations.
The selection of the profile parts used for the fit was checked with the B-I and V-I colour profiles. For an exponential disc, colour profiles are linear. So the chosen parts should be those for which the colour profiles show least deviation from linearity, which was confirmed for the present sample.
For the 11 sample galaxies for which redshifts are available (see Table 2),
disc scalelengths were determined in kpc. The mean values are:
, 
, 
and 
.
These results are in agreement with values found for other samples of
spiral galaxies
(e.g., Kent 1985; van der Kruit 1987;
Andredakis & Sanders
1994; Courteau 1996).
For 13 of the 14 sample galaxies, the disc scalelength decreases
systematically with increasing wavelength.
ESO-LV 235-0080 shows the opposite behaviour,
the disc scalelength increases systematically with increasing wavelength.
For ESO-LV 351-0250,
disc scalelengths increase slightly from I to V, but is
deviating.
ESO-LV 351-0250 is the only galaxy in the present sample for which
an active nucleus was found. Maia et al. (1996) detected [OIII] emission
at a rest wavelength 
.
It is not clear yet if the surface brightness profiles of active
galaxies show systematic differences compared to those of normal galaxies.
Table 6 gives
the mean scalelength ratios and their scatter for the different colours.
| Ratio | mean | scatter |
 | 1.31 | 0.29 |
 | 1.14 | 0.14 |
 | 1.13 | 0.20 |
The systematic increase of disc scalelengths with decreasing wavelength has
already
been found by various authors.
Elmegreen & Elmegreen (1984) obtained
for face-on galaxies. The value found
in this work is larger, which is due to the fact that the present sample
does not include face-on galaxies only but also galaxies with larger
inclination angles, which show larger ratios (see below).
Peletier et al. (1994) found that for bright galaxies with MK < -22 the
ratio of the disc scalelengths in B and K, 
, increases
systematically with increasing apparent ellipticity. Figure 2 (click here) shows disk
scalelength ratios 
, 
and 
for
the present sample. The trend found by Peletier et al. for
is found for the optical and near
infrared wavelength regions as well.
Figure 2: Disc scalelength ratios plotted against apparent ellipticity
measured in the R-filter at 
. a) shows the scalelength ratios between B and
I, b) shows the ratios between
V and I and c) between R and I
The larger the difference in wavelength between the two bands, the larger is the increase of the scalelength ratio with increasing apparent ellipticity. These results confirm that significant colour gradients are present in the discs of the sample galaxies and that these gradients are larger for larger inclination angles.
Byun et al. (1994) simulated galaxy images for different amounts of dust,
determined disc scalelengths and
calculated scalelength ratios
(see their Fig. 10). Unlike the galaxies
investigated in this work,
the model galaxies presented in Fig. 10 do not have bulges. For central
face-on optical depths in the V-band, 
, the
simulated
ratios increase systematically with increasing inclination angle by
. For larger amounts of dust, 
, the ratio is constant or decreases slightly.
This result is not in agreement with the ratios measured in this
work (see Fig. 2 (click here)a). For edge-on galaxies, is about 
larger than for face-on galaxies.
Byun et al. obtained their scalelengths from
major-axis
radial profiles, while in this work scalelengths are measured from
elliptically-averaged profiles. Byun et al. stress that for galaxies with
a significant large differences exist between the two types of profiles,
especially for highly inclined objects.
In the present work however, the fitting ranges for the scalelength
measurements are chosen
to be in the outer parts of the galaxy where the influence of the bulge is
small, so the observed scalelengths should not be significantly affected.
Furthermore, even if one excludes the highly inclined galaxies (e.g.,
objects with 
), Fig. 2 (click here)a is still
not in agreement with any of the model curves.
So even though the comparison is difficult, evidence remains that the
present data show a larger increase of scalelength ratio with increasing
inclination than is predicted by Byun et al. (1994).
Before any final conclusions can be drawn the following steps are necessary: (i) the number of sample galaxies must be enlarged, (ii) for model galaxies with a bulge, scalelength ratios must be calculated from elliptically-averaged profiles, and (iii) the possibility of intrinsic colour gradients within the stellar disc due to population gradients must be taken into account. It is planned to simulate galaxy images with a wider variety of parameters than those used by Byun et al. in order to see if the observed results can be reproduced.
Acknowledgements
I would like to thank Dr. R.S. Stobie for allocation of observing time at SAAO/Sutherland. It is a pleasure to thank Drs. J.W. Menzies and J. Caldwell for assistance during the observations, Mrs. I. Bassett for prereducing the CCD images, and Profs. W.F. Wargau and W. Seitter for many useful discussions concerning galaxies and their properties. Special thanks go to the referee, Dr. F. Simien, for important and helpful comments, and to Dr. R. Dümmler for carefully reading the manuscript. Financial support of this work by the Deutsche Forschungsgemeinschaft DFG under the number Se 345/22-1 and by the Ministerium für Wissenschaft und Forschung des Landes Nordrhein-Westfalen/Germany (Lise-Meitner-Stipendium) is gratefully acknowledged. Finally, I thank ESO for the use of the MIDAS software for the calculation of the surface brightness profiles. This research has made use of the Simbad database at CDS, Strasbourg, France, and of the Lyon-Meudon Extragalactic Database (LEDA) supplied by the LEDA team at the Observatoire de Lyon.
. "Range" gives the range of the semimajor axis in arcsec used
for the fit