First upper limits on the 21-cm signal power spectrum of neutral hydrogen at $z=9.16$ from the LOFAR 3C196 field
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| Main Authors: | , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Ceccotti, E. Offringa, A. R. Mertens, F. G. Koopmans, L. V. E. Munshi, S. Chege, J. K. Acharya, A. Brackenhoff, S. A. Chapman, E. Ciardi, B. Ghara, R. Ghosh, S. Giri, S. K. Höfer, C. Hothi, I. Mellema, G. Mevius, M. Pandey, V. N. Zaroubi, S. |
| author_facet | Ceccotti, E. Offringa, A. R. Mertens, F. G. Koopmans, L. V. E. Munshi, S. Chege, J. K. Acharya, A. Brackenhoff, S. A. Chapman, E. Ciardi, B. Ghara, R. Ghosh, S. Giri, S. K. Höfer, C. Hothi, I. Mellema, G. Mevius, M. Pandey, V. N. Zaroubi, S. |
| contents | The redshifted 21-cm signal of neutral hydrogen from the Epoch of Reionization (EoR) can potentially be detected using low-frequency radio instruments such as the Low-Frequency Array (LOFAR). So far, LOFAR upper limits on the 21-cm signal power spectrum have been published using a single target field: the North Celestial Pole (NCP). In this work, we analyse and provide upper limits for the 3C196 field, observed by LOFAR, with a strong ${\approx}80\,$Jy source in the centre. This field offers advantages such as higher sensitivity due to zenith-crossing observations and reduced geostationary radio-frequency interference, but also poses challenges due to the presence of the bright central source. After constructing a wide-field sky model, we process a single 6-hour night of 3C196 observations using direction-independent and direction-dependent calibration, followed by a residual foreground subtraction with a machine learned Gaussian process regression (ML-GPR). A bias correction is necessary to account for signal suppression in the GPR step. Still, even after this correction, the upper limits are a factor of two lower than previous single-night NCP results, with a lowest $2σ$ upper limit of $(146.61\,\text{mK})^2$ at $z = 9.16$ and $k=0.078\,h\,\text{cMpc}^{-1}$ (with $\text{d}k/k\approx 0.3$). The results also reveal an excess power, different in behaviour from that observed in the NCP field, suggesting a potential residual foreground origin. In future work, the use of multiple nights of 3C196 observations combined with improvements to sky modelling and ML-GPR to avoid the need for bias correction should provide tighter constraints per unit observing time than the NCP. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_18534 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | First upper limits on the 21-cm signal power spectrum of neutral hydrogen at $z=9.16$ from the LOFAR 3C196 field Ceccotti, E. Offringa, A. R. Mertens, F. G. Koopmans, L. V. E. Munshi, S. Chege, J. K. Acharya, A. Brackenhoff, S. A. Chapman, E. Ciardi, B. Ghara, R. Ghosh, S. Giri, S. K. Höfer, C. Hothi, I. Mellema, G. Mevius, M. Pandey, V. N. Zaroubi, S. Cosmology and Nongalactic Astrophysics Instrumentation and Methods for Astrophysics The redshifted 21-cm signal of neutral hydrogen from the Epoch of Reionization (EoR) can potentially be detected using low-frequency radio instruments such as the Low-Frequency Array (LOFAR). So far, LOFAR upper limits on the 21-cm signal power spectrum have been published using a single target field: the North Celestial Pole (NCP). In this work, we analyse and provide upper limits for the 3C196 field, observed by LOFAR, with a strong ${\approx}80\,$Jy source in the centre. This field offers advantages such as higher sensitivity due to zenith-crossing observations and reduced geostationary radio-frequency interference, but also poses challenges due to the presence of the bright central source. After constructing a wide-field sky model, we process a single 6-hour night of 3C196 observations using direction-independent and direction-dependent calibration, followed by a residual foreground subtraction with a machine learned Gaussian process regression (ML-GPR). A bias correction is necessary to account for signal suppression in the GPR step. Still, even after this correction, the upper limits are a factor of two lower than previous single-night NCP results, with a lowest $2σ$ upper limit of $(146.61\,\text{mK})^2$ at $z = 9.16$ and $k=0.078\,h\,\text{cMpc}^{-1}$ (with $\text{d}k/k\approx 0.3$). The results also reveal an excess power, different in behaviour from that observed in the NCP field, suggesting a potential residual foreground origin. In future work, the use of multiple nights of 3C196 observations combined with improvements to sky modelling and ML-GPR to avoid the need for bias correction should provide tighter constraints per unit observing time than the NCP. |
| title | First upper limits on the 21-cm signal power spectrum of neutral hydrogen at $z=9.16$ from the LOFAR 3C196 field |
| topic | Cosmology and Nongalactic Astrophysics Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2504.18534 |