Correction to the top panel of Figure 3 in Mullis et al. 2005
Fig. 3 (top panel) CORRECTED -- Color-magnitude diagram of XMMU J2235.3-2557
Due to a combination of low signal-to-noise in the VLT-FORS2 z-band image and some source blending, Sextractor's MAG_AUTO significantly overestimated the magnitude of the four brightest galaxies on the red sequence shown in the top panel of Figure 3 in Mullis et al. 2005. Though the photometry of the faint spectroscopic members is largely unaffected, the z-band magnitude of the brightest two spectroscopic members is overestimated by two magnitudes and that of the third and fourth brightest by approximately one magnitude (considering here both red and orange symbols as members).
Based on high-quality HST-ACS z-band photometry, Sextractor's aperture-based magnitudes (MAG_APER) of the VLT-FORS2 image provide a much more accurate estimate of the total magnitudes. An updated version of the color-magnitude diagram appears below. Here both R-z color and z-band magnitude (AB) are based on aperture photometry (diameter = 3.5 x FWHM = ~2.4"). The resolution of the z-band image (0.50" FWHM, z_Gunn filter) was degraded to match the R-band image (0.68" FWHM, R_special filter). Sextractor was run in dual-image mode where source detection was based on the original z-band image and the photometry was based on the seeing-matched images.
We reiterate the only procedural difference between the original and corrected versions of the figure is that the total z-band magnitudes in the former are MAG_AUTO whereas those in the latter are MAG_APER.
CRM, 27 September 2005