Quasar candidates with periodic variations from the Zwicky Transient Facility. I. Sample

We conduct a systematic search for quasars with periodic variations from the archival photometric data of the Zwicky Transient Facility (ZTF) by cross matching with the quasar catalogues of the Sloan Digital Sky Survey and V\'eron-Cetty & V\'eron. We first select out primitive periodic candidates using the methods of the generalized Lomb-Scargle periodogram and auto-correlation function, and then estimate the false-alarm probability of the periodicity and calculate the Bayesian information criterion to compare between periodic and purely stochastic models. As such, we finally identify a sample of 127 candidates with the most significant periodic variations out of 143,700 quasars. This is the largest periodic quasar sample so far, thus providing a useful guiding sample for studying origins of quasar periodicity considering the moderate sampling rate and high-quality photometry of the ZTF data. We summarize the basic properties of the sample and briefly discuss the implications.