Host galaxy identification of LOFAR sources in the Euclid Deep Field North

TL;DR

This paper presents a highly complete catalogue of optical and near-infrared counterparts to LOFAR radio sources in the Euclid Deep Field North, including photometric redshifts and detailed identification methods.

Contribution

It introduces a robust identification strategy combining Likelihood Ratio method with visual inspection, achieving a 99.2% match rate for radio sources with host galaxy counterparts.

Findings

Catalogue includes 19,550 sources with reliable counterparts.

Median redshift of sources is 1.1, extending up to z=6.

Approximately 7% are infrared-only detections with median z=3.0.

Abstract

We present a catalogue of optical and near-infrared counterparts to radio sources detected in the Euclid Deep Field North (EDF-N) using observations from the LOw-Frequency ARray (LOFAR) High Band Antenna (HBA) at 144 MHz with 6 arcsec angular resolution. The catalogue covers a circular region of $10deg^2$ and includes 23309 radio sources with a peak signal-to-noise ratio greater than 5. After masking regions close to stars and with unreliable photometry in the optical or near-infrared, the catalogue includes 19550 sources. To carry out a robust identification strategy, we combined the statistical power of the Likelihood Ratio (LR) method, including both colour and magnitude information, with targeted visual inspection. The resulting catalogue boasts a remarkable identification rate of 99.2%, successfully matching 19401 out of 19550 radio sources with reliable optical and/or near-infrared counterparts. For 19391 of the matched sources, we successfully derived photometric redshift for the host galaxy by performing an SED fit using the available data in the optical, near-infrared, far-infrared, and radio. LOFAR sources within the catalogue exhibit a median redshift of 1.1, with some extending up to z=6. Around 7% of the sample is detected only in infrared using IRAC and tends towards higher redshifts, with a median of z=3.0. This comprehensive catalogue serves as a valuable resource for future research, enabling detailed investigations into the properties and evolution of LOFAR-detected sources and their host galaxies.