Galaxy And Mass Assembly (GAMA): mass-size relations of z$<$0.1 galaxies subdivided by S\'ersic index, colour and morphology

TL;DR

This study derives detailed stellar mass-size relations for low-redshift galaxies from the GAMA survey, analyzing how these relations vary with galaxy type, wavelength, and other properties, providing a comprehensive benchmark for high-redshift studies.

Contribution

It offers a robust set of stellar mass-size relations across multiple bands and galaxy classifications, emphasizing the importance of sample selection and the limitations of Sersic index as a separator.

Findings

Galaxies are more compact at longer wavelengths, with a 13% size decrease from g to K_s at 10^10 solar masses.

Sersic index bimodality diminishes at low stellar masses, reducing its effectiveness as a galaxy type separator.

The study provides a detailed, multi-band low-z benchmark for galaxy size relations, improving on previous aperture-based measurements.

Abstract

We use data from the Galaxy And Mass Assembly (GAMA) survey in the redshift range 0.01$<$z$<$0.1 (8399 galaxies in $g$ to $K_s$ bands) to derive the stellar mass $-$ half-light radius relations for various divisions of 'early' and 'late'-type samples. We find the choice of division between early and late (i.e., colour, shape, morphology) is not particularly critical, however, the adopted mass limits and sample selections (i.e., the careful rejection of outliers and use of robust fitting methods) are important. In particular we note that for samples extending to low stellar mass limits ($<10^{10}\mathcal{M_{\odot}}$) the S\'ersic index bimodality, evident for high mass systems, becomes less distinct and no-longer acts as a reliable separator of early- and late-type systems. The final set of stellar mass $-$ half-light radius relations are reported for a variety of galaxy population subsets in 10 bands ($ugrizZYJHK_s$) and are intended to provide a comprehensive low-z benchmark for the many ongoing high-z studies. Exploring the variation of the stellar mass $-$ half-light radius relations with wavelength we confirm earlier findings that galaxies appear more compact at longer wavelengths albeit at a smaller level than previously noted: at $10^{10}\mathcal{M_{\odot}}$ both spiral systems and ellipticals show a decrease in size of 13% from $g$ to $K_s$ (which is near linear in log wavelength). Finally we note that the sizes used in this work are derived from 2D S\'ersic light profile fitting (using GALFIT3), i.e., elliptical semi-major half light radii, improving on earlier low-z benchmarks based on circular apertures.