The new era of Lyman alpha emitters (LAEs): Efficiency in the selection criteria

Abstract: The ODIN survey has detected thousands of Lyman-alpha emitting galaxies across seven sky fields, covering nearly one hundred square degrees. One of these regions is the SHELA field, observed with DECam on the Blanco Telescope, reaching depths of approximately 25.3 AB mag in the N501 and N419 narrowbands and approximately 26.3 AB mag in the g and r broadbands over fifteen square degrees. In this work, we analyze the efficiency of the dual-continuum selection criterion as a function of broadband depth. Applied to the N501/N419 observations, we find that when the broadband data are roughly one magnitude deeper than the narrowband, nearly 80% of the LAEs are recovered, compared to only approximately 20% when both reach the same depth. This result shows that, for a fixed observing budget, the optimal strategy is to obtain broadband images approximately one magnitude deeper than the narrowband, since deeper exposures yield progressively smaller gains in the recovery fraction.