J-HERTz: J-PLUS Heritage Exploration of Radio Targets at z < 5

In this talk, I will present J-HERTz, the J-PLUS Heritage Exploration of Radio Targets at z < 5, a multi-wavelength catalog combining LoTSS DR2 radio data, WISE infrared detections, and J-PLUS DR3 optical narrow-band observations. Covering 2100 deg², J-HERTz includes nearly 500,000 sources, classified into galaxies, QSOs, and stars, along with new photometric redshifts for objects without spectroscopy. A key discovery is a population of radio-loud galaxies with no ongoing nuclear activity, many of which show large-scale radio emission (~185 kpc), suggesting they are AGN relics revealed at low radio frequencies. Using SED fitting from J-PLUS with CIGALE, we analyze the link between radio-loudness, stellar mass, and star formation. Radio-loud galaxies tend to be massive and quenched, while radio-quiet starbursts have much higher specific star formation rates. For QSOs, we find a bimodal distribution of radio-loud and radio-quiet populations, with the radio-loud fraction increasing with redshift, reaching ~20% at z = 3.5-4. Additionally, J-HERTz identifies stars with radio emission, which may be linked to coronal activity or exoplanet interactions, though background contamination must be considered. By combining optical, IR, and radio data, J-HERTz provides new insights into AGN evolution, jet activity, and the nature of radio sources across cosmic time. I will discuss the implications of these findings and their connection to galaxy evolution.