Galaxy And Mass Assembly (GAMA): Galaxy colour gradients versus colour, structure and luminosity

TL;DR

This study investigates radial colour gradients in galaxies from the GAMA survey, revealing bimodal distributions linked to galaxy structure and luminosity, supporting inside-out growth and merger scenarios.

Contribution

It introduces a detailed analysis of intrinsic colour gradients across galaxy populations using multiwavelength data and structural parameters, highlighting bimodal behaviours.

Findings

High- and low-$n$ galaxies show bimodal colour gradient distributions.

Strong negative colour gradients support inside-out growth models.

Blue high-$n$ galaxies exhibit properties of dissipative major mergers.

Abstract

Using single-component fits to SDSS/UKIDSS images of galaxies in the G09 region of the GAMA survey we study radial colour gradients across the galaxy population. We use the multiwavelength information provided by MegaMorph analysis of galaxy light profiles to calculate intrinsic colour gradients, and divide into six subsamples split by overall S\'{e}rsic index ($n$) and galaxy colour. We find a bimodality in the colour gradients of high- and low-$n$ galaxies in all wavebands, which varies with overall galaxy luminosity. Global trends in colour gradients therefore result from combining the contrasting behaviour of a number of different galaxy populations. The ubiquity of strong negative colour gradients supports the picture of inside-out growth through gas accretion for blue, low-$n$ galaxies, and through dry minor mergers for red, high-$n$ galaxies. An exception is the blue high-n population, with properties indicative of dissipative major mergers.