The J-HERTz catalog from J-PLUS & LoTSS

We introduce J-HERTz (J-PLUS Heritage Exploration of Radio Targets at z<5), a new multiwavelength catalog that combines optical narrowband photometry from J-PLUS, infrared observations from the Wide-field Infrared Survey Explorer, and deep low-frequency radio data from LoTSS for nearly 0.5 million sources across 2100 deg2 of the northern sky. Key innovations of J-HERTz include Bayesian neural network classifications for 390,000 galaxies, 31,000 quasars, and 20,000 stars, along with significantly improved photometric redshifts for 235,000 galaxies compared to previous J-PLUS DR3 and LoTSS DR2 estimates.

We identify 831 candidate Galactic radio stars, which, if confirmed, would constitute a significant addition to the number of radio-emitting stars identified to date. Among radio-loud galaxies with spectroscopic observations, >~20% lack Seyfert or LINER signatures, indicating a substantial population of optically quiescent radio galaxies, in agreement with previous works. Spectral energy distribution fitting of their host galaxies using J-PLUS photospectra reveals systematically low specific star formation rates, consistent with quenched stellar populations.