UV-LIGHTS: New tools for revealing the low surface brightness regime in the ultraviolet. Appendices D-E

APPENDICES D and E from UV-LIGHTS: New tools for revealing the low surface brightness regime in the ultraviolet Abstract Ultra-deep optical imaging surveys have reached unprecedented depths (≳30 mag arcsec−2; 3σ, 10′′×10′′), facilitating the study ofvery faint galactic structures. However, the ultraviolet bands, which are key to the study of stellar populations, remain essentiallyunexplored at these depths. In this paper we present a detailed surface brightness and color analysis of the outermost regions of 20nearby galaxies in the LBT Imaging of Galactic Haloes and Tidal Structues (LIGHTS) fields observed by GALEX in the FUV andNUV. We adapt and apply a low surface brightness oriented methodology that has proven effective in ultra-deep optical surveys. Anovel approach to background subtraction is proposed for UV imaging. Instead of subtracting a constant value from the background,we subtract a Poisson distribution that transforms the background into a pseudo-Gaussian distribution centered at zero. Furthermore,the PSF deconvolution algorithms developed for optical data are applied to our sample, using a novel set of very extended (R=750′′)PSFs for the GALEX bands. This methodology allows us to obtain depths ranging from 28.5 to 30 mag arcsec−2 (3σ; 10′′×10′′), withreliable surface brightness profiles up to 31 mag arcsec−2. This is about 1 mag deeper than with standard UV techniques. We use thesurface brightness and color profiles to show that the application of PSF deconvolution, especially in the FUV, effectively mitigatesthe excess of light present in the outer regions of certain galaxies compared to the standard GALEX pipeline. This finding is crucialfor any accurate stellar population inference from the color profiles. Additionally, a qualitative analysis of the results is presented,with particular emphasis on the surface brightness and color properties of the galaxies beyond their optical edges. Our work highlightsthe importance of developing innovative low surface brightness methods for UV surveys.