4 Image analysis

4.1 H-band magnitudes from virtual aperture photometry

At the position of the galaxies' centers (determined by fitting a two-dimensional Gaussian to the galaxies) a growth curve was derived for each object by integrating the counts in concentric circular rings of increasing radii. The background was determined in a concentric object-free corona (where the contribution from contaminating stars is rejected by average sigma-clipping). The measurements taken through the individual "virtual circular apertures'' are useful to compare with existing similarly taken measurements (e.g. Gezari et al. 1993) and for calibration purposes of future observations. They are given in Table 2 (available only in digital format) as follows:
Column 1: Galaxy denomination in the CGCG (Z) or VCC catalogues.
Column 2: aperture diameter in arcsec.
Column 3: logarithmic ratio of the adopted aperture diameter to the optical (a₂₅) diameter.
Column 4: integrated H magnitude within the aperture.

   

Table 2: The "virtual aperture photometry''. This is a one page sample. The entire table containing 6293 entries is only available in electronic format

Galaxy	Ap.	${\rm log} Ap/a_{25}$	H
	arcsec		mag
(1)	(2)	(3)	(4)
Z 97005	3.80	-1.15	15.31
Z 97005	5.80	-.97	14.58
Z 97005	7.70	-.85	14.09
Z 97005	9.60	-.75	13.78
Z 97005	11.50	-.67	13.52
Z 97005	15.40	-.54	13.15
Z 97005	16.70	-.51	13.05
Z 97005	19.20	-.45	12.92
Z 97005	22.50	-.38	12.80
Z 97005	26.90	-.30	12.67
Z 97005	30.70	-.25	12.61
Z 97005	34.60	-.19	12.56
Z 97005	38.40	-.15	12.53
Z 97011	3.80	-.80	14.67
Z 97011	5.80	-.62	14.04
Z 97011	7.70	-.49	13.67
Z 97011	9.60	-.40	13.43
Z 97011	11.50	-.32	13.26
Z 97011	15.40	-.19	13.09
Z 97011	16.70	-.16	13.05
Z 97011	19.20	-.10	13.01
Z 97011	22.50	-.03	12.97
Z 97011	26.90	.05	12.97
Z 97013	3.80	-1.10	16.29
Z 97013	5.80	-.92	15.61
Z 97013	7.70	-.79	15.21
Z 97013	9.60	-.70	14.96
Z 97013	11.50	-.62	14.76
Z 97013	15.40	-.49	14.58
Z 97013	16.70	-.46	14.53
Z 97013	19.20	-.40	14.53
Z 97013	22.50	-.33	14.51
Z 97021	3.80	-.98	12.59
Z 97021	5.80	-.79	12.12
Z 97021	7.70	-.67	11.87
Z 97021	9.60	-.57	11.71
Z 97021	11.50	-.50	11.58
Z 97021	15.40	-.37	11.41
Z 97021	16.70	-.33	11.36
Z 97021	19.20	-.27	11.29
Z 97021	22.50	-.20	11.21
Z 97021	27.10	-.12	11.13
Z 97021	31.50	-.06	11.07
Z 97021	34.90	-.01	11.02
Z 97021	38.40	.03	10.98

The photometry of 159 galaxies observed under photometric conditions has been checked against 187 published aperture photometry measurements (see Gezari et al. 1993). The comparison of our "virtual aperture'' measurements with the reference photometry, taken through apertures consistent with ours, is given in Fig. 3. On the average we find:

$H_{{\rm this~work}} - H_{{\rm literature}}$ = -0.026 $\pm$ 0.095 mag.

The most discrepant measurements are those taken through small apertures (5-15 arcsec), due to a combination of seeing effects and unaccurate galaxy centering. We estimate the overall photometric accuracy of our data, including systematic errors in the calibration, to be $\leq$ 0.1 mag.

Figure 3: The comparison between the present photometric measurements and those available from the literature as a function of the normalized aperture

4.2 Isophotal radii, total magnitudes, and concentration indices

Our NIR observations available so far (including those given in Papers I, II and IV and in B97) were also analyzed using a more sophisticated approach than the one adopted here: 1) the surface brightness profiles were derived from azimuthally averaged elliptical isophotes with center, ellipticity and position angle taken as free parameters. 2) the surface brightness profiles were decomposed into combinations of exponential and de Vaucouleurs laws (or double exponential profiles) using a fitting algorithm. We prefer to postpone the discussion of these profile decompositions to a forthcoming paper (Paper V of this series; some details of the decomposition procedures can be found in Scodeggio et al. 1998). However we wish to anticipate here a few results which depend on the fitting algorithms only as a tool necessary to extrapolate the measured photometry to infinity: i.e. to obtain total magnitudes, concentration indexes and also to derive isophotal radii at a given limiting surface brightness (20.5 mag arcsec^-2in this cse) when the observations do not reach such a limit.

Table 1 gives the H band measured parameters of the observed galaxies, as follows:
Column 18: $H_{{\rm B25}}$ magnitude obtained extrapolating the present photometric measurements to the optical diameter along circular apertures as in Gavazzi & Boselli (1996).
Column 19: $H_{{\rm B25}}^{\rm c}$ magnitude computed at the optical diameter (see Col. 18) corrected for galactic and internal extinction following Gavazzi & Boselli (1996). The adopted internal extinction correction is $\Delta m=-2.5 \, D\, \log(b/a)$ where D = 0.17, as determined in Boselli & Gavazzi (1994).
Column 20: $H_{\rm T}$ total H magnitude extrapolated to infinity along either an exponential or a de Vaucouleurs r^1/4 law fitted to the outer parts of the observed radial surface brightness profiles (see Paper V for details).
Column 21: galaxy observed major (r_H(20.5)) radius (in arcsec) determined in the elliptical azimuthally-integrated profiles as the radius at which the surface brightness reaches 20.5 H-mag arcsec^-2. Galaxies which require a surface brightness extrapolation larger than 0.5 mag to reach the $\rm 20.5^{th}$  magnitude isophote are labelled -1.
Column 22: the model-independent concentration index C₃₁, as defined in de Vaucouleurs (1977), is the ratio between the radii that enclose 75% and 25% of the total light $H_{\rm T}$.