A new sample of faint Blazar cAndidates with Strong opticAl variabiLiTy (BASALT)

We present a sample of blazar candidates from the Very Large Array Sky Survey (VLASS) catalog, with cross-referencing to optical and infrared data from the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) and the Wide-Field Infrared Survey Explorer (WISE), respectively. We focus on compact radio sources and employ a multistage selection process to minimize contamination from non-blazar sources. We considered constraints derived from the radio-optical spectral index and from the infrared and optical colors. We identified the variable objects through an optical variability analysis of Pan-STARRS light curves using two reference samples of stars. We further selected sources whose variability exceeds the level observed in quasars. This led to the selection of 3 467 candidates with blazar-like properties and strong optical variability. Only 45% is available in other blazar candidate catalogs, with the remainder representing new identifications. In particular, we unveil a large population of faint sources, down to r ∼ 20.5. The blazar nature of a subsample of these sources is confirmed by available spectra. Our work offers new insights into the blazar population and serves as a foundation for future variability studies, especially in view of the upcoming Legacy Survey of Space and Time at the Observatory, which will reach even fainter sources. Vera C. Rubin