The present data were compared with aperture photometry available in the literature by integrating the counts in concentric circular rings around the galaxy centres to provide curves of growth up to the diameter of the reference photometry. This operation was made without subtracting stars from the frames since, unless otherwise specified, the aperture photometry is generally not corrected for stellar contamination. Galaxies observed at the 2.2-m telescope in non photometric conditions and with no aperture photometry available in the literature were re-observed at the 3.5 m telescope. The growth curve was used to derive the photometric zero point for galaxies observed in non photometric periods (as indicated in Table 5), and provided a general check of the intrinsic photometric accuracy of the current work. The virtual photometry measurements obtained in this work are consistent in the average with the aperture photometry available in the literature (88 measurements): and . The most discrepant measurements are those at small apertures () due to a combination of seeing effects and galaxy centering, which might be quite inaccurate in the objects with no bright nuclei such as dwarf irregular galaxies.
We estimate that the overall photometric accuracy of our data, including systematic errors on the zero point determination is 0.1 mag.
To facilitate comparison with optical data available in the literature, integrated magnitudes were determined in circular apertures from the star-subtracted frames to the diameter of the 25.5 mag arcsec blue isophote as described and tabulated in Table 3.
Using the star-subtracted frames, the surface brightness profiles were
re-determined by averaging the brightness distribution in concentric elliptical
annuli of fixed centre, position angle and ellipticity. The ellipses were
fitted by eye to the K' band 21 mag arcsec isophotes of the galaxy under
study (for some low-surface brightness galaxies, a weaker isophote had to be used:
the values are given in parentheses in Table 5; see Sect. 4).
This simple technique was preferred to more sophisticated procedures
to be as consistent as possible with the
method we used in optical CCD studies (see Gavazzi et al.
1995a and references therein).
Given the irregular shape of Im and BCD galaxies,
elliptical profiles give just a crude representation of
their real profiles (see Sect. 4).
Starting from an inner ellipse of size comparable with the seeing disk,
a set of annuli, increasing in major axis by fixed amounts was drawn. In each
annulus the total number of counts, pixels and associated statistical
uncertainties were computed following
Gavazzi et al. (1994).
The isophotal major radii () in the H and K' bands were determined from the azimuthally integrated profiles as the radii at which the surface brightness reaches 21.5 mag arcsec. The values of given in this work are not corrected for galaxy inclination.
Magnitudes were derived by integrating the elliptical light profiles up to the radius corresponding to the 21.5 mag arcsec isophote ( and ). Since in some dwarf galaxies 21.5 mag arcsec is too close to the peak brightness to measure a meaningful diameter, we also give and . These entries, which are generally less accurate than and because of the higher noise in the data at the 22.0 mag arcsec isophote, can nevertheless be fairly well determined in the low surface brightness galaxies where longer integration times were used. These magnitudes are observed quantities and are not corrected for extinction. The photometric parameters determined along elliptical rings are summarized in Table 5 (only available in electronic form), as follows:
Column 1: VCC name.
Column 2: adopted filter.
Column 3: total integration time per position (in sec); this corresponds to the product of the exposure time of the elementary integration (generally ) the number of (added) elementary integrations.
Column 4: number of frames per galaxy (combined with a median filter).
Column 5: adopted mosaic, as defined in Sect. 2.2. Some galaxies (marked ) were serendipitously observed in the sky frames of other targets. S indicates large galaxies where an ad hoc designed mosaic was used.
Column 6: pixel size, in arcseconds: these are 0.64 and 1.61 arcsec/pixel for the 2.2-m telescope and 0.81 arcsec/pixel for the 3.5-m telescope.
Column 7: photometric quality: galaxies marked ``'' were observed in non-photometric periods; diameters and magnitudes are not determined; for galaxies marked ``r'' the zero-point was determined using reference aperture photometry.
Column 8: position angle of the galaxy major axis (measured counterclockwise from N).
Column 9: ellipticity (1-b/a).
Column 10: observed major () radius (in arcsec) determined at the magnitude isophote.
Column 11: observed magnitude () integrated within the 21.5 mag arcsec elliptical isophote.
Column 12: concentration index , defined as the ratio between the radii that contain 75% and 25% of .
Column 13: observed major () radius (in arcsec) determined at the magnitude isophote.
Column 14: observed magnitude () integrated within the 22.0 mag arcsec elliptical isophote.
Column 15: concentration index , defined as the ratio between the radii that contain 75% and 25% of .
For galaxies observed at both the 2.2-m and the 3.5-m telescope, Table 5 reports 2 lines. The 3.5-m telescope data refer in fact to the combined images.
Grey-level and contour representations of the K' brightness distribution
of the galaxies studied are given in Fig. 3 (click here) alongside surface
brightness and (where possible) colour profiles.
Table 6 gives the parameters of the differential H and K' band
radial surface brightness
profiles obtained by azimuthal integration along elliptical annuli.
Table 6 (only available in electronic form) is arranged as follow:
Column 1: VCC name.
Column 2: adopted filter.
Column 3: radius (on the major axis) of the elliptical annulus, in arcseconds.
Column 4: surface brightness at the given radius.