Number density of halo stars in NGC 5128 as a function of galactocentric distance a, normalized to the effective radius R_e (upper panel). This calculation assumes a halo elongation e = 0.77 from the inner-halo photometry of Dufour et al. (1979). Black symbols are the ACS and WFPC2 fields from Table 1, and open red symbols are the WFC3 fields. The equation for the power-law fit line is given in the text. Error bars are calculated from Poisson statistics, including the raw number counts in each field, the number of subtracted stars from the decontamination procedure, and the completeness correction. Residuals from the fitted line in the upper panel, plotted vs. azimuthal angle from the isophotal major axis (lower panel). The residuals clearly show a systematic trend with position angle θ_a, indicating that an incorrect ellipticity e has been assumed.