Galaxy And Mass Assembly (GAMA): Bulge-disk decomposition of KiDS data in the nearby universe

TL;DR

This study performs detailed bulge-disk decompositions on over 13,000 nearby galaxies using KiDS data, employing Bayesian modeling and automated selection to produce robust structural parameters for galaxy evolution research.

Contribution

It introduces a fully automated Bayesian fitting approach for bulge-disk decomposition across multiple bands, with rigorous validation and integration into the GAMA database.

Findings

Robust fit results with minimal biases across galaxy types.

Automated model selection accuracy exceeds 90%.

Errors are typically underestimated by factors of 2-3 by MCMC.

Abstract

We derive single S\'ersic fits and bulge-disk decompositions for 13096 galaxies at redshifts z < 0.08 in the GAMA II equatorial survey regions in the Kilo-Degree Survey (KiDS) g, r and i bands. The surface brightness fitting is performed using the Bayesian two-dimensional profile fitting code ProFit. We fit three models to each galaxy in each band independently with a fully automated Markov-chain Monte Carlo analysis: a single S\'ersic model, a S\'ersic plus exponential and a point source plus exponential. After fitting the galaxies, we perform model selection and flag galaxies for which none of our models are appropriate (mainly mergers/Irregular galaxies). The fit quality is assessed by visual inspections, comparison to previous works, comparison of independent fits of galaxies in the overlap regions between KiDS tiles and bespoke simulations. The latter two are also used for a detailed investigation of systematic error sources. We find that our fit results are robust across various galaxy types and image qualities with minimal biases. Errors given by the MCMC underestimate the true errors typically by factors 2-3. Automated model selection criteria are accurate to > 90 % as calibrated by visual inspection of a subsample of galaxies. We also present g-r component colours and the corresponding colour-magnitude diagram, consistent with previous works despite our increased fit flexibility. Such reliable structural parameters for the components of a diverse sample of galaxies across multiple bands will be integral to various studies of galaxy properties and evolution. All results are integrated into the GAMA database.