The LOFAR Two-metre Sky Survey: Deep Fields Data Release 2. I. The ELAIS-N1 field

TL;DR

This paper presents the final high-resolution, highly sensitive LOFAR 144MHz deep field images of the ELAIS-N1 region, cataloging nearly 155,000 radio sources and analyzing their properties, variability, and polarization.

Contribution

It provides the deepest and most sensitive LOFAR images of the ELAIS-N1 field, with a refined source detection approach and comprehensive analysis of source variability and polarization.

Findings

Detected 154,952 radio sources within 24.53 sq. degrees.

Achieved a noise level of 10.7 μJy/beam at 6'' resolution.

Identified 39 variable sources and 3 polarized emitters.

Abstract

We present the final 6'' resolution data release of the ELAIS-N1 field from the LOw-Frequency ARray (LOFAR) Two-metre Sky Survey Deep Fields project (LoTSS Deep). The 144MHz images are the most sensitive achieved to date at this frequency and were created from 290 TB of data obtained from 505 hrs on-source observations taken over 7.5 years. The data were processed following the strategies developed for previous LoTSS and LoTSS Deep data releases. The resulting images span 24.53 square degrees and, using a refined source detection approach, we identified 154,952 radio sources formed from 182,184 Gaussian components within this area. The maps reach a noise level of 10.7 $\mu$Jy/beam at 6'' resolution where approximately half of the noise is due to source confusion. In about 7.4% of the image our limited dynamic range around bright sources results in a further > 5% increase in the noise. The images have a flux density scale accuracy of about 9% and the standard deviation of offsets between our source positions and those from Pan-STARRS is 0.2'' in RA and Dec for high significance detections. We searched individual epoch images for variable sources, identifying 39 objects with considerable variation. We also searched for circularly polarised sources achieving three detections of previously known emitters (two stars and one pulsar) whilst constraining the typical polarisation fraction plus leakage to be less than 0.045%.