CCD CALIBRATION OF THE MAGNITUDE SCALE FOR THE SSRS2 SAMPLE - THE EQUATORIAL REGION

In this paper we continue our investigation on the isophotal nature, accuracy, and uniformity of the magnitude system adopted in the Southern Sky Redshift Survey extension (SSRS2). Extending our earlier work, we examine galaxies in the equatorial region, primarily in the declination range -17.5°≤δ≤0°, over a large range of right ascension, covering the southern and northern Galactic caps. For this purpose, we have obtained CCD isophotal magnitudes in the B and R bands for 265 galaxies of different morphological types. Using this larger sample we confirm our earlier claim that the mSSRS2 magnitudes are very nearly the magnitude measured within the isophote μB=26 mag arcsec-2, with a dispersion of about 0.30 mag. The relative zero-point offset between our mSSRS2 magnitudes and the CCD photometry is -0.02 mag from all data we have obtained. However, we detect a variation of the zero-point across different regions of the sky of ±0.10 mag for regions at large angular separations. We also estimate that the zero-point offset between the mSSRS2 and Zwicky systems is relatively small (≈0.10 mag), which should allow us to combine the data from the SSRS2 and the CfA2 Redshift Survey.