Star formation at the edge of galaxies

At the edge of galaxies, in the lowest surface brightness regimes, lies the boundary where gas can collapse to form new stars. These regions remain largely unexplored due to the lack of very deep images that allow us to characterize the star-forming clumps at the edge of the discs. In this sense, we do not know whether stellar activity in these very low-density regions is similar to that in the more central regions of galaxies. To answer this question, we use the ultra-deep (limiting surface brightness 31 mag/arcsec^2) images of the LIGHTS survey obtained with the LBT in g and r bands, and the very deep Halpha data obtained with the INT telescope. In this presentation, we will show for the first time how different the distribution of shapes, sizes and fluxes of star-forming regions at the edges of galaxies is compared to the active zones in the central parts of galaxies. We will discuss the implications of this discovery for understanding the current rate at which galaxy discs are growing.