Gaia Data Release 3 Specific processing and validation of all sky RR Lyrae and Cepheid stars: The Cepheid sample

Context. Cepheids are pulsating stars that play a crucial role in several astrophysical contexts. Among the different types, the Classical Cepheids are fundamental tools for the calibration of the extragalactic distance ladder. They are also powerful stellar population tracers in the context of Galactic studies. The Gaia Third Data Release (DR3) publishes improved data on Cepheids collected during the initial 34 months of operations. Aims. We present the Gaia DR3 catalogue of Cepheids of all types, obtained through the analysis carried out with the Specific Object Study (SOS) Cep&RRL pipeline. Methods. We discuss the procedures adopted to clean the Cepheid sample from spurious objects, to validate the results, and to reclassify sources with an incorrect outcome from the SOS Cep&RRL pipeline. Results. The Gaia DR3 includes multi-band time-series photometry and characterisation by the SOS Cep&RRL pipeline for a sample of 15 006 Cepheids of all types. The sample includes 4663, 4616, 321, and 185 pulsators, distributed in the Large and Small Magellanic Cloud, Messier 31, and Messier 33, respectively, as well as 5221 objects in the remaining All Sky subregion which includes stars in the Milky Way field and clusters and in a number of small satellites of our Galaxy. Among this sample, 327 objects were known as variable stars in the literature but with a di fferent classification, while, to the best of our knowledge, 474 stars have not been reported as variable before now and therefore they likely are new Cepheids discovered by Gaia.