Table 2
Composition of the main sample used in this work.
| Class | No. of sources | Fraction |
|---|---|---|
| Stars | 27 985 913 | 90.875% |
| Galaxies | 150 581 | 0.489% |
| Low-z QSOs and AGNs | 16 269 | 0.053% |
| High-z QSOs | 1908 | 0.006% |
| Other(*) | 2172 | 0.007% |
| Unclassified | 2 639 184 | 8.570% |
Notes. The last line represents the sources for which we could not find a spectroscopic classification, nor significant proper motion or parallax measurements in the Gaia catalog, hence it is the subset we use to search for new high-z (z > 2.5) QSO candidates (Sect. 7). (*)Any other spectral classification, such as Type 2 AGN, HII region, BL Lac, etc.
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