Optical Counterparts of MeerKLASS L-band and UHF-band surveys

M. Klein, S. Mangla, J. Mohr, S. Chatterjee, K. Grainge, S. Paul, M. G. Santos, O. M. Smirnov, C. Tasse, L. Wolz

First listed 2026-08-07 | Last updated 2026-08-06

Abstract

Context: Wide-area radio continuum surveys require reliable optical and infrared counterpart identification, but high optical source densities and extended or multi-component radio morphologies make this challenging. Aims: We present optical and infrared counterpart catalogs for MeerKLASS L-band and UHF-band on-the-fly continuum sources using KiDS DR5 and DESI Legacy Imaging Surveys DR10 (LS DR10), including counterpart probabilities, redshifts, and host-galaxy properties. Methods: We developed the Stellar-mass Enhanced Density Association (SEDA) method, an empirical framework that compares candidate densities around radio positions with those in a position-displaced control catalog. For galaxies we use positional offset, stellar mass, and redshift; quasar candidates are treated separately using offset and mid-infrared selection. A second-pass search associates multi-component radio sources with common hosts. Results: In the L-band survey, we identify 20,400 KiDS-based counterparts with $P_{\rm true}>0.5$, corresponding to 66% of L-band sources within the KiDS footprint. In the UHF-band survey, we identify 61,633 LS DR10 counterparts, corresponding to 81% of the radio sources. Spectroscopic redshifts are available for 22% and 44% of the L-band and UHF-band counterparts, respectively. The redshift distributions show low-redshift star-forming galaxies, intermediate-redshift radio galaxies, and a high-redshift tail dominated by quasars. SEDA also recovers rare radio-loud quasars, including QSO J2318-3113 at $z=6.44$ and UHF_DR1 J+111111.8+053626.6 at $z=5.24$. Conclusions: SEDA provides a data-driven route to counterpart identification for wide-area radio surveys with complex source morphologies. The catalogs enable future MeerKLASS studies of radio source populations, host-galaxy demographics, and rare high-redshift radio quasars.

Short digest

Klein et al. build optical/infrared counterpart catalogs for MeerKLASS DR1 L-band and UHF-band radio sources, introducing the Stellar-mass Enhanced Density Association (SEDA) method to distinguish real hosts from chance alignments using offset, stellar mass, redshift, and a separate mid-infrared quasar treatment. At P_true > 0.5, they identify 20,400 KiDS counterparts for 66% of L-band sources and 61,633 LS DR10 counterparts for 81% of UHF sources, with a second-pass procedure recovering hosts of multi-component radio systems. The matched populations trace low-redshift star-forming galaxies, intermediate-redshift radio galaxies, and a quasar-dominated high-redshift tail, including radio-loud QSO J2318-3113 at z=6.44 and UHF_DR1 J+111111.8+053626.6 at z=5.24. The work supplies a morphology-aware, empirical association framework that turns wide MeerKLASS continuum catalogs into samples usable for host-demographic and rare early-quasar studies.

Key figures to inspect

• Figure 4. This is the core SEDA diagnostic: it shows how counterpart probability varies jointly with radio-optical separation and stellar mass for z>0.4 candidates, establishing the physical and statistical basis for preferring massive plausible hosts over nearby field interlopers.
• Figure 9. The probability and purity calibration provides the practical justification for the P_true threshold used throughout the catalog, comparing real radio positions with displaced controls and linking individual association probabilities to sample-level reliability.
• Figure 13. The L-band and UHF counterpart redshift distributions synthesize the catalog outcome, making visible the transition from low-redshift star-forming systems through radio galaxies to the high-redshift quasar tail emphasized in the paper.
• Figure 15. The radio-luminosity--stellar-mass plane separates the host-galaxy locus from WISE-selected quasar candidates, connecting the association catalog to the underlying mixture of massive radio galaxies and quasar-dominated sources.
• Figure 16. This figure directly documents the rare high-redshift payoff of the matching procedure, including the z=6.44 L-band quasar QSO J2318-3113 and the z=5.24 UHF quasar UHF_DR1 J+111111.8+053626.6.