Left: Systematics of TESS survey and light curve extraction technique indicated by the PSDs of non-variable galaxy light curves, where the y-axis is the scaled power relative to the constant white noise. Each gray line indicates the power law plus white noise fit for an individual galaxy’s light curve, the black line represents the mean galaxy PSD, and the red and yellow shaded areas represent the one-sigma and three-sigma limits, respectively. Right: Comparison between Seyfert 1 AGN, ESO 362-G018, Sector 5 PSD (which has the measured t_min, ul value equal to the median of the AGN sample), and the upper limits of galaxies as a representative to illustrate the measurement of the shortest detected variability timescale. The text next to the PSD lists the parameters for the best fit. The PSDs in both panels are normalised by their respective noise levels.