A catalog of quasar candidates identified by astrometric and mid-infrared methods in Gaia EDR3

We obtain a quasar candidate catalog of 1,119,806 sources by using appropriate ALLWISE [W1-W2] color and different combinations of astrometric criteria, which contains 990,525 candidates (88.5%) in common with the Gaia EDR3_AGN catalog and 129,281 newly identified quasar candidates. Together with the contamination and completeness, the magnitude, astrometric properties, density distribution, and the morphological indexes of these selected quasars are evaluated. The completeness of this catalog is around 70%, and the reliability is estimated to be better than 94%. After removing the quasar candidates with significant astrometric residuals, we obtain a catalog with 672,161 quasar candidates with the best astrometric behaviors. Compared to the Gaia EDR3 frame rotator sources, there are 353,185 more sources in this catalog, which could be used to characterize the reference frame and the astrometric solution of Gaia more accurately.