The local luminosity function at 25 microns

The local luminosity function at 25 mu m provides the basis for interpreting the results of deep midinfrared surveys planned or in progress with space astrophysics missions including the Infrared Space Observatory (ISO), Wide-Field Infrared Explorer (WIRE), and Space Infrared Telescope Facility (SIRTF). We have selected a sample of 1458 galaxies from the IRAS Faint Source Survey with a flux density limit of 250 mJy at 25 mu m. The local luminosity function is derived using both parametric 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 Local Supercluster. A maximum likelihood fit to the radial density shows 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 the prior estimates to have been strongly affected by the Local Supercluster. Our new luminosity function leads to lower estimates of midinfrared backgrounds and number counts.