The Infrared Luminosity Function of Galaxies

Abstract

We used spectroscopic data from the Sloan Digital Sky Survey (SDSS) and photometric data from the Wide-Field Infrared Survey Explorer (WISE) to create a luminosity function of almost 200,000 galaxies in the WISE1 (W1) 3.4-micron band. This was made possible by the highsignal-to-noise ratios of WISE data, which allowed us to create a luminosity function which depended on only the selection function in SDSS. We compared these results with the r-band luminosity function to find that there is a significantly higher luminosity density in the W1band, with j ≈ 6.605 × 10hL Mpc−3 in the infrared W1-band and j ≈ 1.75× 10hL Mpc−3 in the optical r-band. Young, massive stars emit most of their light in optical wavelengths, but contain only a small amount of a galaxy’s stellar mass, contributing a disproportionate amount of light to stellar mass. As a result, the W1-band allows us to get a better estimate of the overall stellar mass, since the galaxy luminosity function in the infrared and near-infrared is less sensitive to recent star formation histories and extinction due to interstellar dust. The color-magnitude diagrams from both bandpasses indicate that the most luminous galaxies are also redder in color.