Apparent luminosity function of galaxies to the twenty-first magnitude

The galaxy distribution was probed in depth by counts to several limiting magnitudes rather than survey a large a ea at the same limiting magnitude. reducing camera was built and used at the Cassegrain foci of the 36- and 82-inch telescopes at McDonald Observatory. Photographs were taken of 13 fields in the north galactic pola r cap, each field covering 0.346 square degree (36-inch) and 0.066 square degree (82-inch). A decision was made as to whether each object was a galaxy or a star and its identity and position within a counting square plotted on a large scale chart of each plate. Since the four plates for each area were approximately concentric, this made possible checks on the identity of objects on each 36-inch plate by a deeper plate. The limiting magnitude of each plate was obtained by a combination of photoelectric and photographic photometry. Four standard stars (12 to 14 mag.) were measured photoelectrically in each area. A computer model for fixed aperture ''Schilt type'' photograhic photometry was written and used to extrapolate from the photoelectric standards to the plate limit. As a check pulse count photometry was done with the 82-inch telescope on faint stars and galaxies in three of the photographed areas. The apparent luminosity function for galaxies (B = 17.7 to 21.0) so derived was compared with results from others. A computer model for the apparent luminosity function was written. It integrates over the absolute luminosity function of the types of galaxies most likely to have been counted, and includes type-dependent K-corrections. The model is compared with means of data from all sources. The effects of galaxy evolution and intergalactic extinction are considered. Also additional evidence is provided that galaxies are not distributed homogeneously in depth. (U.S.)