Custom ZTF photometry for classification

Finally, we compared our AGN candidate sample with those identified through colour selection and X-ray detection techniques. We find that the fraction of low-z quiescent galaxies exhibiting significant variability drops dramatically (from 98% of the sample to 7% of the sample, when using the standard variability metric Pvar) when replacing the DR11-psf light curves with our difference image, aperture photometry (DI-Ap) version.

The overall number of variable low-z AGN remains high (99% when using DR11-psf light curves, 83% when using DI-Ap); however, it implies that our photometry can detect the fainter variability in host dominated AGN. The classifier effectively distinguishes between AGN and other sources, demonstrating high recovery rates even for AGN in resolved nearby galaxies. AGN candidates in eROSITA's eFEDS field, detected in X-rays and bright enough for ZTF optical observations, were classified as AGN (79%) and non-variable galaxies (20%).

These groups show a 2dex difference in X-ray luminosity, but not in X-ray flux. A significant fraction of X-ray AGN are optically too faint for ZTF, and conversely, one-quarter of ZTF AGN in the eFEDS area lack X-ray detections, highlighting a wide range of X-ray-to-optical flux ratios in the AGN population.