Nearby Galaxies in the 2micron All Sky Survey I. K-band Luminosity Functions

TL;DR

This study presents detailed K-band luminosity functions for nearby galaxies, revealing distinct patterns across morphological types and implications for black hole mass distribution in the local universe.

Contribution

It provides the first comprehensive K-band luminosity functions segregated by galaxy morphology, highlighting the bimodal nature of bulge luminosities and their contribution to the local luminosity density.

Findings

Late-type spirals have a power-law LF rising at low luminosities.

Ellipticals and bulge-dominated spirals show peaked LFs declining at extremes.

Bulges contribute 30% to the local K-band luminosity density.

Abstract

Differential K-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 towards 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-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-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 in the local universe with spiral disks making up the remainder. If bulge luminosities indicate central black hole masses, then our results predict that the black hole mass function is also bimodal.