The model specifications that I'm fitting now include a number of such models, of which "mg4x2px" is the most general (two free ellipses, each described by four Gaussians). The table in this notebook suggests (unsurprisingly) that it is the best-fitting model for most galaxies out of a sample of ~2000:
profit.hst.mg4x2px.chisqred.1 1417
profit.hst.mg8bpx.chisqred.1 194
profit.hst.mg4bpx.chisqred.1 143
profit.hst.mg8serserbpx.chisqred.1 74
profit.hst.serb.chisqred.0 67
profit.hst.serbpx.chisqred.0 58
profit.hst.mg4serserbpx.chisqred.1 11
There are also some plots with direct comparisons to double Sersic fits, showing that mg4x2px provides small but non-negligible improvements in reduced chi-squared for most galaxies. I expect the improvements would be larger in multi-band fitting as Gaussian mixtures allow for color gradients within components.
Having said that, mg4x2px has 30-odd free parameters and is extremely expensive to fit. The fact that 'mg4bpx' - which is the equivalent model with just one component - is a better fit ~10% of the time despite being strictly less complex also indicates that the two-component variant is difficult to fit robustly (unsurprisingly). While there are less complex variations that we could test (e.g. with a scale radius and fixed size ratios instead of four free sizes, as implemented in DM-18585), we are focusing on choosing and optimizing single-component models for the near future. After that, we might take a closer look at using these more complex models as the ground truth, especially for multi-band fitting.
Story
The model specifications that I'm fitting now include a number of such models, of which "mg4x2px" is the most general (two free ellipses, each described by four Gaussians). The table in this notebook suggests (unsurprisingly) that it is the best-fitting model for most galaxies out of a sample of ~2000:
profit.hst.mg4x2px.chisqred.1 1417
profit.hst.mg8bpx.chisqred.1 194
profit.hst.mg4bpx.chisqred.1 143
profit.hst.mg8serserbpx.chisqred.1 74
profit.hst.serb.chisqred.0 67
profit.hst.serbpx.chisqred.0 58
profit.hst.mg4serserbpx.chisqred.1 11
There are also some plots with direct comparisons to double Sersic fits, showing that mg4x2px provides small but non-negligible improvements in reduced chi-squared for most galaxies. I expect the improvements would be larger in multi-band fitting as Gaussian mixtures allow for color gradients within components.
Having said that, mg4x2px has 30-odd free parameters and is extremely expensive to fit. The fact that 'mg4bpx' - which is the equivalent model with just one component - is a better fit ~10% of the time despite being strictly less complex also indicates that the two-component variant is difficult to fit robustly (unsurprisingly). While there are less complex variations that we could test (e.g. with a scale radius and fixed size ratios instead of four free sizes, as implemented in
DM-18585), we are focusing on choosing and optimizing single-component models for the near future. After that, we might take a closer look at using these more complex models as the ground truth, especially for multi-band fitting.