PYRAMID MAXIMUM-ENTROPY IMAGES OF IRAS SURVEY DATA

In this paper we present a new method for the construction of high-res olution images from the IRAS survey data base. The method, Pyramid Max imum Entropy (PME), is a special application of multi-channel maximum entropy image construction techniques, using pyramid images in which e ach of the (K + 1) image channels covers the same map area, but contai ns 2k x 2k (k = 0, 1,..., K) pixels. The final result is a 2K x 2K-pix el image. PME is a two-dimensional application of the MEMSYS5 software package. As PME explicitly includes spatial correlations in the image s, it is capable of reconstructing emission at virtually any relevant scale length. MEMSYS5 provides the capability to compute an error esti mate of the MaxEnt result(s). PME uses this feature to calculate an er ror map: a map of error estimates of the corresponding image pixel val ues. This is a powerful tool for determining the reliability of the re sults. It allows us to quantify point source fluxes as well as flux de nsities in diffuse areas, e.g., the disks of galaxies. We present imag es in all four survey wavelength bands (12, 25, 60, and 100 mum) of th ree nearby galaxies with different morphologies, to illustrate the qua lity of the PME results. A summary of the principles of Bayesian image (re)constrUction, on which PME is based, and the mathematical foundat ion for incorporating spatial correlations in images are included in t wo appendices.