- 4.1 Magnitudes
- 4.2 Diameters
- 4.3 Concentration indices
- 4.4 Ellipticities and Position Angles
- 4.5 Non-axisymmetric structures

*Column 1*: UGC number or, if missing, CGCG
number;

*Column 2*: Other common names;

*Column 3 and 4*: Equatorial J2000 coordinates in standard units
(*hh mm ss.s, dd mm ss*);

*Column 5*: Revised Hubble morphological type from the RC3;

*Column 6*: Total *B* magnitude or, if missing,
photographic magnitude reduced to the system, from
the RC3;

*Column 7*: Isophotal optical size, major (*D _{25}*) and minor axes in
arcmin at 25

*Column 8*: Heliocentric systemic velocity in km s^{-1} as
listed in NED^{},
or, if missing, from private archives;

*Column 9*: "Total'' *H* magnitude () within a circle of aperture
*D _{25}*;

*Column 10*: Isophotal *H* magnitude (*H _{21.5}*) within the elliptical isophote at 21.5

*Column 11*: Major axis (*D _{21.5}*) in arcmin of the elliptical isophote at 21.5

*Column 12*: Effective diameter () in arcmin; this is the major axis
of the elliptical isophote containing half of the flux corresponding to
;

*Column 13*: Concentration index *C _{31}*, defined as the ratio between the
major axes of the ellipses enclosing 75% and 25% of the flux corresponding
to

*Column 14*: Ellipticity of the outer elliptical isophotes;

*Column 15*: Position angle (PA) of the outer elliptical isophotes, computed
Eastward from North;

*Column 16*: Telescope of observation: TIRGO (T), NOT (N),
and VATT (V);

*Column 17*: Estimate
(*FWHM*) of the seeing disk of observation in arcsec,
see Sect. 3.4.

*Column 18*: Notes from the catalogues.

The total magnitude measures the
flux contained within a circular aperture the size of the optical
diameter *D _{25}*.
For our images this is always an extrapolated value and is computed with
a procedure similar to the one outlined in Gavazzi & Boselli (1996)
and Gavazzi et al. (1996a), although the values here are not corrected for
extinction and redshift.
We estimate the average accuracy of to be 0.15
mag, half the error being contributed by noise and calibration and half
by uncertainty in the extrapolation.

The isophotal magnitude *H _{21.5}* is derived by integrating
the surface brightness radial profile from the center out to the
elliptical isophote at 21.5

As for the relation between the two types of magnitudes, we find
, exactly what was
found for the sample in Gavazzi et al. (1996a).
The relation between the two *H* magntudes is illustrated in Fig. 5,
where their difference is plotted vs. the magnitude itself and
vs. the average *H* surface magnitude. Given the already quoted
accuracies for the two magnitudes, the distribution appears to consist
of a normal range, for 0.3 mag,
and by a deviant tail for the higher values. Such large differences
are partly due to the inclusion of some faint spurious objects,
such as foreground stars superimposed on the outer disk.
In general, the points for the extrapolated values, that is
when also *H _{21.5}* had to be estimated by extrapolation
of the brightness profile, are distributed similarly to the
others, which implies that, as expected, most of the variance is
contributed by . A significant correlation is evident
between and

We conclude that the
accuracy in estimating our *H* magnitudes,
especially the total magnitudes ,
degrades for the faintest galaxies
of the sample, and that an appreciable part
of the error is systematic in the sense of yielding
too bright values for fainter *H _{21.5}* and/or
.
Such a trend spells a word of caution for the use of
heavily extrapolated magnitudes in, say, distance
measurements such as the Tully-Fisher relation.

Since the difference is ideally determined only by the outer disk, we note that, for an exponential disk with folding length , such difference depends only on , the ratio between the isophotal radius and the folding one:

if is identified with the total, asymptotic magnitude of the disk. Also, if is the disk central surface magnitude: In the left panel of Fig. 5, the dashed lines are curves of constant , while in the right panel they are curves of constant . The average (outer) disk appears to have an isophotal radius , with a central brightness
Figure 6 illustrates the comparison between our *D _{21.5}* and the

The ratio between the isophotal optical and NIR diameters is
found to be a weak function of the galaxy colour. This is illustrated in
the upper panel of Fig. 7 where the ratio is plotted
against the total *B*-*H* index, .
The solid curve represents an exponential disk with a central
*B*-*H*=3.5 mag and different scale lengths in the two bandpasses;
for this special value of the central colour (3.5=25-21.5)
the ratio *D _{21.5}*/

The effective diameter reported in Col. 12 of Table 3 is the major axis in arcmin of the fitted elliptical isophote containing half the flux corresponding to the total magnitude . The average uncertainty, not including the error on is about 2% but can be worse, up to 10%, in case of peculiarly disturbed morphologies.

Ten of the sample galaxies, that is 6% of the total,
are reported to host active nuclei, either Seyferts or LINERS or starbursts;
they are marked with solid symbols in Fig. 8.
While in the present sample they are quite luminous, there is no particular tendency
to high *C _{31}* values; also the distribution among the morphological types
is rather uniform but for the avoidance at .We find no difference, for

Figure 9:
,
the average NIR surface brightness within the isophote
at 21.5 H-mag arcsec^{-2} vs. the apparent H magnitude (left panel)
and vs. the isophotal D diameter (right panel).
As in Fig. 6, different symbols refer to different ranges
of optical axial ratios_{21.5} |

Figure 9 is a scatter diagram of the average surface brightness
within the 21.5 *H*-mag arcsec^{-2} isophote versus *H _{21.5}* and vs.

It turns out that such a blind, although objective, procedure is often inaccurate. Indeed, an inspection of the radial profiles of and PA in Fig. 4 shows that they are often determined by the geometry of the spiral pattern, which often dominates even in the NIR, rather than by the effective orientation of the disk. This is true in particular for late spirals seen nearly face on and, obviously, for the more disturbed, peculiar morphologies. In addition our images have a restricted field of view and are somewhat shallower than the plates from which the optical values were estimated and therefore our estimate of the outer disk can be, in some cases, rather uncertain. As a consequence, the values we derive sometimes deviate considerably from those reported in the catalogues, which are also shown for comparison in Fig. 4. A direct comparison of our ellipticities, , and those from the RC3, , is shown in Fig. 10. As expected the scatter is rather large and not appreciably influenced by the most uncertain values; we count 25 galaxies out of 174 for which .It is also quite clear that most discrepant values are found for low-inclination objects, where tends to be definitely larger than .

In a certain number of cases, the isophotal fitting, although strongly influenced by non-axisymmetric structures in the inner regions, is able to recover the actual and PA of the outer disk. These cases (20) are characterized by sudden and strong jumps in their and PA profiles. A good example is UGC 12039, which has both a strong bar and strong spiral arms. As shown in Fig. 11, the radial profiles of , , and PA all show an obvious jump at 20 arcsec, that is right after the fading of the bar. In the same figure we also show the profile obtained by imposing a fixed and PA value, 0.29 and respectively, which are the average values for the outer regions. The influence of the bar on the derived surface brightness profile is clearly depicted, with the strongest deviations reaching 0.5 mag. However, in these cases, the global photometric parameters (magnitudes, diameters, indices) estimated in the two ways are virtually identical, with differences well within the limits of the quoted accuracy. For uniformity with the rest of the sample, and given the small bearing on the global parameters, we prefer to retain also in case of strong asymmetries the fitting procedure with free and PA. In turn this yields the observed and PA profiles, together with higher order azimuthal Fourier components of the luminosity distribution (Carter 1978), which will be used in a forthcoming paper of this series to investigate the properties of bars and non-axisymmetric structures in general.

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