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

TL;DR

J-HERTz is a comprehensive multi-wavelength catalog combining optical, infrared, and radio data, with advanced classification and redshift estimation, enabling studies of radio sources, galaxy evolution, and stellar radio emission.

Contribution

It introduces a new multi-wavelength catalog with Bayesian neural network classifications and improved photometric redshifts for nearly half a million sources, enhancing radio-optical synergy studies.

Findings

Identification of 831 candidate Galactic radio stars.

Over 20% of radio-loud galaxies lack Seyfert or LINER signatures.

Spectral energy distribution fitting shows low star formation rates in host galaxies.

Abstract

We introduce J-HERTz (J-PLUS Heritage Exploration of Radio Targets at $z < 5$), a new multi-wavelength catalog that combines optical narrow-band photometry from J-PLUS, infrared observations from WISE, and deep low-frequency radio data from LoTSS for nearly half a million sources across 2,100 deg$^2$ 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, $\gtrsim$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. J-HERTz thus provides a powerful dataset to exploit radio-optical synergies, enabling studies that span from the origin of stellar radio emission to the AGN life cycle and the role of jet activity in shaping host galaxy evolution.