Optimization of a Choice of X-Match Radius on Gaia Sky

Abstract

We employ Gaia DR3 main catalogue and synthetic generated datasets to perform cross-match and obtain numerically metrics predicting probability of mismatch depending on radius of matching and positional accuracy of matched dataset, as well as of the surface density in the vicinity and stellar magnitude of a source. Gaia DR3 main catalogue was probed for the metrics of distribution to nearest neighbouring source depending on sky coordinates. It was demonstrated that the fraction of true positive outcomes starts decreasing dramatically with increase of dimensionless relation of positional accuracy of matched dataset to characteristic distance to the nearest neighbour when it exceeds 0.2. Simultaneously, while positional accuracy of the matched datasets is close to characteristic distance of the datasets, the probability of true positive and false positive outcomes are similar. It was demonstrated that employing “best neighbour” condition one may decrease the fraction of mismatches up to an order of magnitude, especially in the populated regions of sky and at larger positional errors of matched datasets. Use of stellar magnitudes to constrain the results of positional cross-match is deficient for faint magnitudes. We have calculated probable fraction of mismatches depending on celestial coordinates for cross-match between Gaia and synthetic catalogues having positional uncertainty similar to the one of 2MASS and of eRASS. The lower estimates of expected fraction of mismatches is, in the most populated regions of the sky (Center of the Galaxy and Galactic disk) up to 15% for nearest neighbour and up to 4% for best neighbour criterion, for 2MASS positional accuracy. For eRASS positional accuracy, the respective numbers are up to 91% and up to 12%. We provide metrics of distribution of distance to the nearest neighbour in Gaia DR3 main catalogue in analytical and numerical form, as well as in the form of Python module gaia_density.

Keywords: Cross-match of astronomical surveysGaia