Open Access
Table 1.
Summary of the systematics of each galaxy that we used to recover the OR.
| Systematics | Type | Definition | Main origin | Selection effect |
|---|---|---|---|---|
| Level | A | Detection threshold (in the r-band) above background | Background sky luminosity; CCD temperature, etc. | Fainter objects will be lost from an area of observation where Level is higher. |
| PSF_size | A | Full-width at half-maximum of the r-band point-spread function in arcseconds | Seeing | The blurring could cause small or faint objects to drop below detection thresholds. |
| PSF_ell | B | Ellipticity (1 − q), where q is the 2D major/minor axis ratio) of the r-band point-spread function. | Distortions on the focal plane | Non-isotropic blurring of object isophotes may induce a directional dependence for detections. |
| EXTINCTION_r | C | Galactic extinction in the r-band derived from the Schlafly & Finkbeiner (2011) coefficients for the Schlegel et al. (1998) dust map | The Milky Way | Dust preferentially scatters short-wavelength light from extragalactic objects; the loss of flux could prevent detection. |
| GAIA_nstar | C | The number of Gaia DR3 (Gaia Collaboration 2016; 2023) stars with 14 < G < 17 within 5 arcmin around each KiDS source. | The Milky Way | Light from star-dense regions obscures background objects, and can also result in spurious galaxy detections through the misidentification of PSF-blurred, or blended, stars as galaxies. |
Notes. The second column indicates the spatial variance type: inter-tile (type A), intra-tile (type B), and tile-independent (type C). The other columns indicate their definitions, physical origins, and how they potentially select the galaxy sample.
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