Galaxy And Mass Assembly (GAMA): $\mathcal{M_\star}-R_{\rm e}$ relations of $z=0$ bulges, discs and spheroids

TL;DR

This study performs detailed bulge and disc decomposition on thousands of local galaxies to analyze their stellar mass and size relations, improving measurement robustness and comparing results with simulations and high-redshift data.

Contribution

Introduces a novel fitting approach with repeated parameter variation to reduce failures and improve error estimates in galaxy profile measurements.

Findings

Robust stellar mass-size relations for bulges, discs, and spheroids at z=0.

Comparison of local relations with EAGLE simulations and high-redshift data.

Highlights the importance of consistent data processing for galaxy evolution studies.

Abstract

We perform automated bulge + disc decomposition on a sample of $\sim$7500 galaxies from the Galaxy And Mass Assembly (GAMA) survey in the redshift range of 0.002$<$z$<$0.06 using SIGMA, a wrapper around GALFIT3. To achieve robust profile measurements we use a novel approach of repeatedly fitting the galaxies, varying the input parameters to sample a large fraction of the input parameter space. Using this method we reduce the catastrophic failure rate significantly and verify the confidence in the fit independently of $\chi^2$. Additionally, using the median of the final fitting values and the 16$^{th}$ and 84$^{th}$ percentile produces more realistic error estimates than those provided by GALFIT, which are known to be underestimated. We use the results of our decompositions to analyse the stellar mass - half-light radius relations of bulges, discs and spheroids. We further investigate the association of components with a parent disc or elliptical relation to provide definite $z=0$ disc and spheroid $\mathcal{M_\star}-R_{\rm e}$ relations. We conclude by comparing our local disc and spheroid $\mathcal{M_\star}-R_{\rm e}$ to simulated data from EAGLE and high redshift data from CANDELS-UDS. We show the potential of using the mass-size relation to study galaxy evolution in both cases but caution that for a fair comparison all data sets need to be processed and analysed in the same manner.