THE LOCAL LUMINOSITY FUNCTION AT 25 MICRONS

The local luminosity function at 25 mu m provides the basis for interp reting the results of deep midinfrared surveys planned or in progress with space astrophysics missions including the Infrared Space Observat ory (ISO), Wide-Field Infrared Explorer (WIRE), and Space Infrared Tel escope Facility (SIRTF). We have selected a sample of 1458 galaxies fr om the IRAS Faint Source Survey with a flux density limit of 250 mJy a t 25 mu m. The local luminosity function is derived using both paramet ric and nonparametric maximum likelihood techniques and the classical 1/V-max estimator. Comparison of these results shows that the 1/V-max estimate of the luminosity function is significantly affected by the L ocal Supercluster. A maximum likelihood fit to the radial density show s no systematic increase that would be caused by density evolution of the galaxy population. The density fit is used to correct the 1/V-max estimate. We also demonstrate the high quality and completeness of our sample by a variety of methods. The luminosity function derived from this sample is compared with previously published estimates, showing t he prior estimates to have been strongly affected by the Local Supercl uster. Our new luminosity function leads to lower estimates of midinfr ared backgrounds and number counts.