4.2.2 Determination of Magnitudes

For each galaxy we construct a cleaned image from the original image by substituting the pixels contaminated by signal from other objects with the model values from the ellipse fit. From the cleaned images we determine the following four magnitude quantities

• ${m_{\rm ell}}(r)$: the magnitude within the fitted ellipse with equivalent radius r
• ${m_{\rm circ}}(r)$: the magnitude within a circle with radius r
• $\mu(r)$: the surface brightness at the fitted ellipse with equivalent radius r
• ${< \hspace{-3pt} \mu \hspace{-3pt}>}(r)$: the mean surface brightness within the fitted ellipse with equivalent radius r

The intensities in ADU are transformed to magnitudes using the sky level, the exposure time and an arbitrary zero point of 22. The surface brightnesses are transformed to ${^{\rm m} /{\rm arcsec}^{2}}$ using the CCD scale determined from the astrometry (Sect. , p. ).