The influence of Red Spiral Galaxies on the Shape of the Local K-Band Luminosity Function

TL;DR

This study analyzes how red spiral galaxies influence the shape of the local K-band luminosity function, revealing their significant presence among faint and bright galaxies and their role in galaxy classification.

Contribution

It provides the first detailed analysis of red spirals' impact on the local luminosity function across different magnitudes and morphologies.

Findings

Red spirals comprise 20-50% of all spirals with -25 <= M_K < -20.

Red spirals are as common as early-types at fainter magnitudes (M_K > -24).

Bright red spirals often have ongoing star formation or faded disks.

Abstract

We have determined K-band luminosity functions for 13,325 local Universe galaxies as a function of morphology and color (for K_tot <= 10.75). Our sample is drawn from the 2MASS Extended Source Catalog, with all sample galaxies having measured morphologies and distances (including 4,219 archival redshift-independent distances). The luminosity function for our total sample is in good agreement with previous works, but is relatively smooth at faint magnitudes (due to bulk flow distance corrections). We investigated the differences due to morphological and color-selection using 5,417 sample galaxies with NASA Sloan Atlas optical colors and find that red spirals comprise 20 to 50% of all spirals with -25 <= M_K < -20. Fainter than M_K = -24, red spirals are as common as early-types, explaining the different faint end slopes (alpha = -0.87 and -1.00 for red and early-types, respectively). While we find red spirals comprise more than 50% of all M_K < -25 spiral galaxies, they do not dominate the bright end of the overall red galaxy luminosity function, which is dominated by early-type galaxies. The brightest red spirals have ongoing star formation and those without are frequently misclassified as early-types. The faintest ones have an appearance and Sersic indices consistent with faded disks, rather than true bulge dominated galaxies.