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Astron. Astrophys. 351, 869-882 (1999)

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2. The optical and infrared data

The near-infrared data used in this paper come from the CIO catalog (Gezari et al. 1993 , 1997), which is a compilation of the NIR observations published before 1995. They are given in a large variety of systems (magnitudes [FORMULA], [FORMULA], [FORMULA], etc.) and units. The data are converted to J, H and K magnitudes, using the calibrations of the filters of Bessel & Brett (1988) - which assume that the magnitude of Vega is 0.03 in each band -, and are reduced from the wavelength [FORMULA] to the central wavelengths of the J ([FORMULA]), H ([FORMULA]) and K ([FORMULA]) filters with the following color equations:

  • if [FORMULA],

    [EQUATION]

  • if [FORMULA],

    [EQUATION]

  • if [FORMULA],

    [EQUATION]

  • if [FORMULA],

    [EQUATION]

where [FORMULA] and [FORMULA] are the typical [FORMULA] and [FORMULA] colors of a normal galaxy and depend very little on the galaxy type or the aperture. Color equations using [FORMULA] or [FORMULA] rather than [FORMULA] have also been tested, but the results differ by less than 0.02 mag.

The CIO data are corrected for the Galactic extinction. The NIR extinction is computed from the B-band value [FORMULA] given by the RC3 catalog (de Vaucouleurs et al. 1991) and the extinction curve of Fluks et al. (1994) as follows: [FORMULA].

The magnitudes are also corrected for the redshift z as [FORMULA]. Values of the k-corrections [FORMULA] are given in Table 1 for different types of galaxies and have been computed using the pégase model of spectral evolution (Fioc & Rocca-Volmerange 1997). They should be used only at [FORMULA]. The redshift is taken from the NED database. For a few galaxies, z is unknown and we compute the k-correction (but not the absolute magnitudes) assuming [FORMULA], the mean redshift of our catalog.


[TABLE]

Table 1. k-corrections in B, J, H and K as a function of the type.


The RC3 provides us also with the morphological type T, the ratio [FORMULA] of the major axis ([FORMULA]) to the minor axis of the ellipsis corresponding to the isophot [FORMULA], the total B-magnitude [FORMULA] extrapolated to an infinite radius and the circular effective aperture [FORMULA] containing half the light emitted in the B-band.

When available, we prefer to take [FORMULA] and [FORMULA] from the more recent catalog Hypercat (Prugniel & Héraudeau 1998). This catalog also gives the photometric type [FORMULA] corresponding to the best-fitting growth curve [FORMULA] of the B-magnitude as a function of the circular aperture A, where [FORMULA] (see Appendix A).

[FORMULA] is also corrected for the redshift ([FORMULA]) and the Galactic extinction ([FORMULA]).

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© European Southern Observatory (ESO) 1999

Online publication: November 16, 1999
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