VizieR Online Data Catalog: Gaia FPR. Analysis of QSO environment (Gaia Collaboration+, 2024)

The Gaia Focus Product Release (FPR) provides a catalogue of the quasars environment for the search of gravitational lenses (I/361/lenscand). This catalogue contains 501385 multiplets found within 6" of known quasars (I/361/lenscatn). We analyse the combinations of the components of 476207 such multiplets with 2-6 components in table2.dat and report the most promising candidates in table3.dat.

The analysis done in table2.dat relies on four different methods:

i) When Gaia spectra are available for all the components in the combination, a comparison of the component spectra is done using a reduced chi-square approach, described in Equations 1 (Chi2r) and 2 (Gof) of (Gaia Collaboration+, 2024). This approach is complemented by another technique based on the Wasserstein distance presented in Equation 3 (SWd) of the same manuscript. Auxiliary data computed along this comparison (integrated flux, colours, resampling chi-square and S/N of the spectra) are concurrently provided in table2.dat.

ii) For combinations composed of three or four components, we compute a discriminant value, called the extremely randomized trees (ERT) score. This score reflects the ability for the combination to be matched to the image positions and relative magnitudes produced through simulations of gravitational lens systems. See (Delchambre et al., 2019A&A...622A.165D) for details.

iii) For the 3 760 032 QSOs contained in our input list of quasars, we compute a lens score based on Gaia DR3 (2023A&A...674A...1G) and unWISE (2014AJ....147..108L) data. The handling of missing data in these catalogues and the subsequent imputation of a lens score is done using the Heuristical Ensemble Splitting Imputation and Organization of Data (HESIOD) outlier detection method.

iv) Finally, we combine the spectra comparison scores (Chi2r, Gof and SWd); the ERT scores (SertABCD, SertABC, SertABD, SertACD and SertBCD) and the HESIOD score (SHesiod) with the galactic latitude, (GLAT); maximal separation between pair of components (Size); G magnitudes (GmagMin and GmagMax); minimal S/N (SnrMin); integrated fluxes (Fmin and Fmax) and maximal absolute difference in colours (Dcolor) into a combined score (Scomb) using a Random Forest classifier (2001MachL..45....5B).

The 381 lens candidates considered as promising (ranked 'A') or plausible candidates (ranked 'B') are provided in table3.dat along with their lens scores.

(2 data files).