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Session 11 - Instrumentation & Techniques.
Oral session, Monday, June 09
North Main Hall A,

[11.05] Modified Surface Brightness Fluctuation Technique for Determining Relative Distances between Elliptical Galaxies

E. L. Gates, J. T. McGraw (UNM)

Knowing distances to galaxies is crucial to understanding galaxy cluster dynamics and the structure of the universe. Tonry and Schneider (1988) demonstrated that spatial surface brightness fluctuations (SBFs) of elliptical galaxies and spiral galaxy cores can be used as distance indicators. We modified their basic technique to find relative distances between galaxies to within a few percent. Our analysis focuses primarily on understanding the geometrical effects of a galaxy's surface brightness distribution and how signal-to-noise of the SBFs affects the 2-D spatial power spectrum. Modifications to the SBF method allow us to better analyze the effects of both white and Poisson noise (i.e., read-out noise and photon noise) and background subtraction errors. We modified the SBF technique by gridding the galaxy image into regions and by not subtracting the underlying galaxy surface brightness. These modifications allow us to analyze the power spectra ratios vs. surface brightness ratios for the various regions of the galaxies. Distinct trends in plots of the power spectra ratios vs. the surface brightness ratios appear when either errors in background subtraction or noise dominate the SBF data.

To demonstrate the feasibility and accuracy of our modified SBF technique and the analysis tools we derived, we used both simulations and archive HST V- and I-band data from WF/PC2 for Virgo Cluster and other elliptical galaxies for which adequate signal-to-noise data were available. We also used published V-I colors and Mg_2 measurements of the galaxies to correct for errors in the calculated relative distances caused by differences in the stellar luminosity function. We compare our distance ratios to distances published elsewhere using the standard SBF method, D_n-\sigma method, and other available distance data. Thus, we derive a fully diagnostic method for finding relative distances between galaxies and compare it to other distance finding methods.

Program listing for Monday