The Million Quasars (Milliquas) Catalogue, v6.4
Eric W. Flesch

TL;DR
The Milliquas v6.4 catalogue compiles nearly two million quasars, candidates, and related objects from multiple surveys, providing extensive data including Gaia astrometry, and is publicly accessible for research use.
Contribution
This release updates and expands the quasar catalogue with new objects, multi-wavelength data, and Gaia astrometry, offering a comprehensive resource for astronomical studies.
Findings
Includes 757,991 confirmed quasars and 1.1 million candidates.
Provides Gaia-DR2 astrometry for most objects.
Contains all-sky radio/X-ray associated candidates.
Abstract
Announcing the release v6.4 of the Milliquas (Million Quasars) quasar catalogue which presents all published quasars to 11 December 2019, including SDSS-DR16. Its totals are 757,991 type-I QSOs/AGN and approx 1.1M high-confidence (80%+ likelihood) quasar candidates from SDSS-based & AllWISE photometric quasar catalogs, plus all-sky radio/X-ray associated candidates available only here. Type-II and Bl Lac objects are also included, plus candidates/galaxies with double radio lobes (so calculated), bringing the total count to 1,968,377. Gaia-DR2 astrometry is given for most objects. The catalogue is available on its home page and on NASA HEASARC.
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