use simplifies the background correction while having no effect on the results. Only 60 mas WFC3/IR images are available for the XDF so a second 60 mas multiband catalog was created for the XDF, matched to the 30 mas catalog, and used only for WFC3/IR colours.

Structural parameters {#sec:galfit}
---------------------

GALFIT [@peng2002] was used to determine $I_{814}$-band structural parameters by fitting a single component Sérsic model to the $F814W$ image of every object brighter than $F814W < 28$ mag with <span style="font-variant:small-caps;">SExtractor</span> $\mathtt{FLAGS}
< 4$ in the catalogs.

We used <span style="font-variant:small-caps;">PSFEx</span> [@bertin2011] to supply GALFIT with point spread functions (PSFs) for each object. For each image, a sample of point sources was selected from a shallower <span style="font-variant:small-caps;">SExtractor</span> catalog with the cuts $1.0 <
\mathtt{FWHM} < 10.0$ pixels, $\mathrm{S/N} \geq 5$ and ellipticity $e < 0.3$. A cubic polynomial was used to map the variability of the PSF across the image.

Similar to [@vanderwel2012], the provided reduced images and RMS maps were combined to produce total noise maps to pass to GALFIT. The RMS maps created by Drizzle account for the “instrinsic" sources of noise, e.g. dark current, readout noise, and background noise [@koekemoer2011]. The Poisson noise from the 