Empirical completeness assessment of the Gaia DR2, Pan-STARRS 1, and ASAS-SN-II RR Lyrae catalogues

RR Lyrae stars are an important and widely used tracer of the most ancient populations of our Galaxy, mainly due to their standard candle nature. The current availability of large-scale surveys of variable stars is allowing us to trace the structure of our entire Galaxy, even in previously inaccessible areas like the Galactic disc. In this work, we aim to provide an empirical assessment of the completeness of the three largest RR Lyrae catalogues available: Gaia DR2, PanSTARRS-1, and ASAS-SN-II. Using a joint probabilistic analysis of the three surveys we compute 2D and 3D completeness maps in each survey's full magnitude range. At the bright end (G < 13), we find that ASAS-SN-II and Gaia are near 100 per cent complete in RRab at high latitude (vertical bar b vertical bar > 20 degrees); ASAS-SN-II has the best completeness at low latitude for RRab and at all latitudes for RRc. At the faint end (G > 13), Gaia DR2 is the most complete catalogue for both RR Lyrae types, at any latitude, with median completeness rates of 95 per cent (RRab) and > 85 per cent (RRc) outside the ecliptic plane (vertical bar beta vertical bar > 25.). We confirm high and uniform completeness of PanSTARRS-1 RR Lyrae at 91 per cent (ab) and 82 per cent (c) down to G similar to 18, and provide the first estimate of its completeness at low galactic latitude (vertical bar b vertical bar <= 20 degrees) at estimated medians 65 per cent (ab) and 50-60 per cent (c). Our results are publicly available as 2D and 3D completeness maps, and as functions to evaluate each survey's completeness versus distance or per line of sight.