we describe the two datasets used in this work. In §\[sec:photometry\], we describe the photometry of the UDG candidates in the context of S-PLUS, and in §\[sec:sedfitting\], we present the method developed to determine their stellar populations using a Bayesian framework. In §\[sec:discussion\], we present our results and discuss the main implications of our work for our understanding of the nature of UDGs. We conclude and summarize this work in §\[sec:conclusion\]. Throughout, we assume a standard $\Lambda$CDM cosmology whenever necessary, assuming $H_0=70$ km s$^{-1}$ Mpc$^{-1}$. All magnitudes use the AB system [@1964ApJ...140..689O; @1983ApJ...266..713O].

Data {#sec:data}
====

SMUDGes sample
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Our ability to locate galaxies have been limited both by the lack of sensibility and instrumental constraints, and various attempts have been made to optimize observations at low surface brightness [e.g. @2001ApJS..137..117G; @2015ApJ...809L..21M; @2014PASP..126...55A]. However, there have been no systematic attempt to use current, large volume archival data to search for galaxies, which have not been identified before because standard pipelines are not optimized to find such systems. The project [@2019ApJS..240....1Z] was conceived to develop an automatized way to search for galaxies over a large area of the sky using data from the Legacy imaging survey [@2019AJ....157..168D], a deep three-band observational 