Non-parametric galaxy morphology from stellar and nebular emission with the CALIFA sample

Abstract

Aims. We present a non-parametric morphology analysis of the stellar continuum and nebular emission lines for a sample of local galaxies. We explore the dependence of the various morphological parameters on wavelength and morphological type. Our goal is to quantify the difference in morphology between the stellar and nebular components. Methods. We derived the non-parametric morphological indicators of 364 galaxies from the Calar Alto Legacy Integral Field Area (CALIFA) Survey. To calculate those indicators, we applied the StatMorph package on the high-quality integral field spectroscopic data cubes, as well as to the most prominent nebular emission-line maps, namely [O III]λ5007, Hα, and [N II]λ6583. Results. We show that the physical size of galaxies, M20 index, and concentration have a strong gradient from blue to red optical wavelengths. We find that the light distribution of the nebular emission is less concentrated than the stellar continuum. A comparison between the non-parametric indicators and the galaxy physical properties revealed a very strong correlation of the concentration with the specific star formation rate and morphological type. Furthermore, we explore how the galaxy inclination affects our results. We find that edge-on galaxies show a more rapid change in physical size and concentration with increasing wavelength due to the increase in the optical free path. Conclusions. We conclude that the apparent morphology of galaxies originates from the pure stellar distribution, but the morphology of the interstellar medium presents differences with respect to the morphology of the stellar component. Our analysis also highlights the importance of dust attenuation and galaxy inclination in the measurement of non-parametric morphological indicators, especially in the wavelength range 4000−5000 Å.