Histogram of i-band magnitude of HSC–FIRST RGs (black line) and those with reduced χ2 of the SED fitting smaller than 5.0 (gray region), where i-band magnitude is corrected for the Galactic foreground extinction (see Section 2.2). The vertical dashed line is the threshold (i = 21.3 mag) between SDSS-level and HSC-level RGs.