Pushing the frontiers of low-frequency radio astronomy: An ultra-deep sub-arcsecond LOFAR image of ELAIS-N1

Abstract

We present ultra-deep sub-arcsecond radio images of the ELAIS-N1 field covering 2.5x2.5 deg^2, produced from 200 hours of LOw Frequency ARray (LOFAR) observations in the 115-168 MHz band. The radio continuum images are obtained using recent advances in LOFAR long-baseline calibration and imaging. We achieve a central point-source sensitivity of 5.3 μJy/beam at an angular resolution of 0.33"x0.39" and an area-weighted sensitivity of 7.4 μJy/beam at 0.36"x0.45", making these the deepest radio images below 1.28 GHz to date and among the deepest at any radio frequency. By combining our data with previously released deep 6" LOFAR images, we compile a catalogue with a total of 62,916 unique radio sources across 2.5x2.5 deg^2. Our calibration strategy, combined with astrometric alignment using 95 Gaia quasars, results in positional offsets of ΔRA = -3 ± 27 mas and ΔDEC = 2 ± 17 mas for these same sources. We further demonstrate the potential for deep polarisation studies at sub-arcsecond resolution with instrumental leakages from Stokes I into linear polarisation down to 0.12%, which is about a factor of two better than the typical leakage in the LOFAR Two-metre Sky Survey at 6" resolution. Our results demonstrate that imaging a large number of observations over a wide field area at sub-arcsecond resolution is now computationally feasible. This establishes a new benchmark for low-frequency radio imaging in terms of combining depth, resolution, and survey area, which lays the foundation for deeper and wider surveys in the LOFAR2.0 and SKA era.

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BibTeX RIS

BibTeX

@misc{jong2026pushing,
  title = {{Pushing the frontiers of low-frequency radio astronomy: An ultra-deep sub-arcsecond LOFAR image of ELAIS-N1}},
  author = {J. M. G. H. J. de Jong and L. K. Morabito and R. J. van Weeren and J. B. R. Oonk and A. Ahmadi and P. N. Best and C. L. Hale and R. Kondapally and G. Lusetti and H. J. A. Röttgering and T. W. Shimwell and F. Sweijen and R. Timmerman and M. van der Wild},
  howpublished = {arXiv},
  year = {2026},
  month = nov,
  doi = {10.48550/arxiv.2611.06152},
  eprint = {2611.06152},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2611.06152},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Pushing the frontiers of low-frequency radio astronomy: An ultra-deep sub-arcsecond LOFAR image of ELAIS-N1
AU  - J. M. G. H. J. de Jong
AU  - L. K. Morabito
AU  - R. J. van Weeren
AU  - J. B. R. Oonk
AU  - A. Ahmadi
AU  - P. N. Best
AU  - C. L. Hale
AU  - R. Kondapally
AU  - G. Lusetti
AU  - H. J. A. Röttgering
AU  - T. W. Shimwell
AU  - F. Sweijen
AU  - R. Timmerman
AU  - M. van der Wild
PY  - 2026
DA  - 2026/11/04
PB  - arXiv
DO  - 10.48550/arxiv.2611.06152
UR  - https://arxiv.org/abs/2611.06152
AB  - We present ultra-deep sub-arcsecond radio images of the ELAIS-N1 field covering 2.5x2.5 deg^2, produced from 200 hours of LOw Frequency ARray (LOFAR) observations in the 115-168 MHz band. The radio continuum images are obtained using recent advances in LOFAR long-baseline calibration and imaging. We achieve a central point-source sensitivity of 5.3 μJy/beam at an angular resolution of 0.33"x0.39" and an area-weighted sensitivity of 7.4 μJy/beam at 0.36"x0.45", making these the deepest radio images below 1.28 GHz to date and among the deepest at any radio frequency. By combining our data with previously released deep 6" LOFAR images, we compile a catalogue with a total of 62,916 unique radio sources across 2.5x2.5 deg^2. Our calibration strategy, combined with astrometric alignment using 95 Gaia quasars, results in positional offsets of ΔRA = -3 ± 27 mas and ΔDEC = 2 ± 17 mas for these same sources. We further demonstrate the potential for deep polarisation studies at sub-arcsecond resolution with instrumental leakages from Stokes I into linear polarisation down to 0.12%, which is about a factor of two better than the typical leakage in the LOFAR Two-metre Sky Survey at 6" resolution. Our results demonstrate that imaging a large number of observations over a wide field area at sub-arcsecond resolution is now computationally feasible. This establishes a new benchmark for low-frequency radio imaging in terms of combining depth, resolution, and survey area, which lays the foundation for deeper and wider surveys in the LOFAR2.0 and SKA era.
ER  -

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