Measuring Distances Using Infrared Surface Brightness Fluctuations

Surface brightness fluctuations (SBFs) are much brighter in the IR than theyare at optical wavelengths, making it possible to measure greater distancesusing IR SBFs. We report new K' (2.1 micron) SBF measurements of 9 galaxies inthe Fornax and Eridanus clusters using a 1024^2-pixel HgCdTe array. We usedimproved analysis techniques to remove contributions from globular clusters andbackground galaxies, and we assess the relative importance of other sources ofresidual variance. We applied the improved methodology to Fornax and Eridanusimages and to previously published Virgo cluster data. Apparent fluctuationmagnitudes were used in conjunction with Cepheid distances to M31 and the Virgocluster to calibrate the K' SBF distance scale. We find the absolutefluctuation magnitude MK'= -5.61+/-0.12, with an intrinsic scatter to thecalibration of 0.06 mag. No statistically significant change in MK' is detectedas a function of (V-I). Our calibration is consistent with constant age andmetallicity stellar population models. The lack of a correlation with (V-I) inthe context of the stellar population models implies that elliptical galaxiesbluer than (V-I)=1.2 have SBFs dominated by younger (5-8 Gyr) populations. K'SBFs prove to be a reliable distance indicator as long as the residual variancefrom globular clusters and background galaxies is properly removed. Also, it isimportant that a sufficiently high S/N ratio be achieved to allow reliable skysubtraction because residual spatial variance can bias the measurement of theSBF power spectrum. (abridged)Comment: Accepted for publication in ApJ, 44 pages, 10 Postscript figure