SURFACE BRIGHTNESS FLUCTUATIONS IN NGC-5128 FROM WIDE-FIELD PHOTOGRAPHIC PLATES

Deep R- and B-band photographic plates of NGC 5128, obtained under pho tometric conditions at the f/3.3 prime focus of the AAT 3.9 m telescop e, clearly show surface brightness fluctuations from the luminous, ste llar population. The variance of these fluctuations has been used by T onry and collaborators to determine distances to nearby galaxies. Howe ver, certain discrepancies have arisen with independent primary calibr ators over comparable distance scales. We exploit the distinct statist ical proper-ties of photographic plates when compared with CCDs to pro vide an independent analysis of the luminosity fluctuations. We demons trate that the threshold and saturation levels of a detector skew the statistics at both extremes. Our model successfully accounts for the f irst three statistical moments of the photographic grain response meas ured from the density wedges on the photographic plates. We show that the statistical phases of the individual variance sources are uncorrel ated if the analysis is restricted to a narrow photographic exposure r ange. After removing the grain noise component, the derived form of th e power spectrum for the seeing-convolved luminosity fluctuations is i n good agreement with those recently published by Tonry & Schechter [A J, 100, 1794 (1990)] in the V and I bands. In the R band, we determine a value of 3.8 +/- 1.1 Mpc for the distance to NGC 5128. Although les s accurate, our approach constitutes a statistically independent test and therefore provides strong support for Tonry's luminosity fluctuati on distance method.