Galaxy And Mass Assembly (GAMA): Understanding the wavelength dependence of galaxy structure with bulge-disc decompositions

TL;DR

This study uses bulge-disc decompositions of GAMA survey galaxies to analyze how galaxy structural parameters like Sersic index and effective radius depend on wavelength, revealing intrinsic properties of galaxy components and their color gradients.

Contribution

It provides new insights into the wavelength dependence of galaxy structure and color distributions, highlighting the intrinsic nature of disc properties and the variation of bulge and disc colors with galaxy type.

Findings

Most disc galaxies show high Sersic index variation with wavelength.

Radial stellar population and dust effects cause wavelength-dependent structural changes.

Bulge and disc colors vary systematically with galaxy total color and brightness.

Abstract

With a large sample of bright, low-redshift galaxies with optical$-$near-IR imaging from the GAMA survey we use bulge-disc decompositions to understand the wavelength-dependent behavior of single-S\'ersic structural measurements. We denote the variation in single-S\'ersic index with wavelength as $\mathcal{N}$, likewise for effective radius we use $\mathcal{R}$. We find that most galaxies with a substantial disc, even those with no discernable bulge, display a high value of $\mathcal{N}$. The increase in S\'ersic index to longer wavelengths is therefore intrinsic to discs, apparently resulting from radial variations in stellar population and/or dust reddening. Similarly, low values of $\mathcal{R}$ ($<$ 1) are found to be ubiquitous, implying an element of universality in galaxy colour gradients. We also study how bulge and disc colour distributions vary with galaxy type. We find that, rather than all bulges being red and all discs being blue in absolute terms, both components become redder for galaxies with redder total colours. We even observe that bulges in bluer galaxies are typically bluer than discs in red galaxies, and that bulges and discs are closer in colour for fainter galaxies. Trends in total colour are therefore not solely due to the colour or flux dominance of the bulge or disc.