# Galapagos-2/Galfitm/GAMA -- multi-wavelength measurement of galaxy structure: separating the properties of spheroid and disk components in modern surveys

**Authors:** Boris Häußler, Marina Vika, Steven P. Bamford, Evelyn J. Johnston, Sarah Brough, Sarah Casura, Benne W. Holwerda, Lee S. Kelvin, Cristina Popescu  
**arXiv:** [2204.05907](https://arxiv.org/abs/2204.05907)  
**Date:** 2022-04-12  
**Summary page:** https://www.summarizepaper.com/en/paper/2204.05907v1/

## Key points

- Galapagos-2 and Galfitm are tools for fitting two-component profiles to galaxies
- They aim to provide multi-band, multi-component fitting of large samples of galaxies in future surveys
- The authors released both the code and fit results to 234,239 objects from the DR3 of the Gama survey - a sample significantly deeper than previous works
- Multi-band fitting using Galfitm provides significant benefits when attempting to decompose galaxies into their individual components
- Using simulated data, they find that multi-band fitting significantly reduces deviations from real parameter values and allows component sizes and S\'ersic indices to be recovered more accurately
- On both simulated and real data, the authors confirm that the spectral energy distributions (SEDs) of the two main components can be recovered to fainter magnitudes compared to single-band fitting
- Comparing their results with those provided by other fitting codes reveals general agreement but measurement errors can be reduced by using the multi-band tools developed by MegaMorph project
- Multi-band fitting employed by Galapagos-2 and Galfitm significantly improves accuracy in structural galaxy parameters and enables much larger samples for scientific analysis - an important step towards complete understanding of galaxy structure through multi-component fits in future surveys

## Summary

Galapagos-2 and Galfitm are powerful tools for fitting two-component profiles to galaxies with the aim of providing multi-band, multi-component fitting of large samples of galaxies in future surveys. In this study, the authors release both the code and fit results to 234,239 objects from the DR3 of the Gama survey - a sample significantly deeper than previous works. They use stringent tests on simulated and real data to evaluate the advantages of using multi-band over single-band data. The authors demonstrate that multi-band fitting using Galfitm provides significant benefits when attempting to decompose galaxies into their individual components. By effectively being able to utilise colour information buried in individual exposures, more data can be used to improve accuracy. Using simulated data, they find that multi-band fitting significantly reduces deviations from real parameter values and allows component sizes and S\'ersic indices to be recovered more accurately. Additionally, it constrains band-to-band variations of these parameters to more physical values. On both simulated and real data, the authors confirm that the spectral energy distributions (SEDs) of the two main components can be recovered to fainter magnitudes compared to single-band fitting which tends to recover disks and bulges with identical SEDs when galaxies become too faint instead of their true different SEDs. Comparing their results with those provided by other fitting codes reveals general agreement but measurement errors can be reduced by using the multi-band tools developed by MegaMorph project. The authors conclude that multi-band fitting employed by Galapagos-2 and Galfitm significantly improves accuracy in structural galaxy parameters and enables much larger samples for scientific analysis - an important step towards complete understanding of galaxy structure through multi-component fits in future surveys.