Nearby galaxies in the 2 μm all sky survey. I. K-band luminosity functions

Differential K_s -band luminosity functions (LFs) are presented for a complete sample of 1613 nearby bright galaxies segregated by visible morphology. The LF for late-type spirals follows a power law that rises toward low luminosities whereas the LFs for ellipticals, lenticulars, and bulge-dominated spirals are peaked and decline toward both higher and lower luminosities. Each morphological type (E, S0, S0/a-Sab, Sb-Sbc, Sc-Scd) contributes approximately equally to the overall K_s -band luminosity density of galaxies in the local universe. Type averaged bulge/disk ratios are used to subtract the disk component leading to the prediction that the K _s -band LF for bulges is bimodal with ellipticals dominating the high luminosity peak, comprising 60% of the bulge luminosity density in the local universe with the remaining 40% contributed by lenticulars and the bulges of spirals. Overall, bulges contribute 30% of the galaxy luminosity density at K_s in the local universe with spiral disks making up the remainder. If bulge luminosities indicate central black hole (BH) masses, then our results predict that the BH mass function is also bimodal.