The Local Galaxy 8 μ m Luminosity Function

A Spitzer Space Telescope survey in the NOAO Deep-Wide Field in Boötes provides a complete, 8 μm-selected sample of galaxies to a limiting (Vega) magnitude of 13.5. In the 6.88 deg field sampled, 79% of the 4867 galaxies have spectroscopic redshifts, allowing an accurate determination of the local (z < 0.3) galaxy luminosity function. Stellar and dust emission can be separated on the basis of observed galaxy colors. Dust emission (mostly PAH) accounts for 80% of the 8 μm luminosity, stellar photospheres account for 19%, and AGN emission accounts for roughly 1%. A sub-sample of the 8 μm-selected galaxies have blue, early-type colors, but even most of these have significant PAH emission. The luminosity functions for the total 8 μm luminosity and for the dust emission alone are both well fit by Schechter functions. For the 8 μm luminosity function, the characteristic luminosity is νL∗ν(8.0 μm) = 1.8 × 10 10 L⊙ while for the dust emission alone it is 1.6×10 L⊙. The average 8 μm luminosity density at z < 0.3 is 3.1 × 10 L⊙ Mpc , and the average luminosity density from dust alone is Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 Jet Propulsion, California Institute of Technology, Mail Stop 169-506, Pasadena, CA91109 School of Physics, Monash University, Clayton 3800, Victoria, Australia Steward Observatory, University of Arizona, 933 N Cherry Ave., Tucson, AZ 85121 Spitzer Science Center, Caltech, 1200 E. California, Pasadena, CA 91125 Department of Astronomy, The Ohio State University, 140 West 18th Ave., Columbus, OH 43210 Department of Astrophysics, Oxford University, Keble Rd, Oxford, OX1 3RH, U.K. Current address: Department of Physics and Astronomy, George Mason University, 4400 University Drive, MS 3F3, Fairfax, VA 22030