Hydrogen spin-flip radiation at cosmological redshifts

[Dimitry UA3AVR]

Hi everybody.

The LOFAR project also included plans to observe the HI line at 1420 MHz from distant objects with redshifts of z > 5, https://arxiv.org/abs/astro-ph/0610596. Perhaps someone knows the current status of this objective. I haven't come across many publications dedicated to observing high-redshift hydrogen, though it is quite possible i have missed something.

Mny regards, Dimitry UA3AVR.

[Dimitry UA3AVR]

Chat GPT tells that still no such radiation with z>5 is detected, https://chatgpt.com/s/t_6a6eee1255b48191ad5ad74d66ff1502.

воскресенье, 2 августа 2026 г. в 09:04:26 UTC+3, Dimitry UA3AVR:

[Adrian]

Hi Dimitry,

As well as you, I have also been looking forward to any reports of the detection of such a high Z‑ H I line verification event. Although I have not conducted an exhaustive search of the recent literature, I assume that if this detection occurs there should be fairly widespread news reports of the discovery, at least in the more science‑oriented news media outlets.

As I understand it, for example, the Murchison Widefield Array was specifically designed and constructed to detect the 21 cm line from neutral hydrogen at redshifts Z=6 and greater, up to about Z ≈  10 , as this corresponds to the Epoch of Reionization that is of interest in the cosmological chronology of the early universe.

As you mentioned, other observatories such as LOFAR, PAPER, and HERA have also not reported detection of the signal.

Unfortunately, I also think that this detection has not happened mainly due to the high levels of foregrounds, ionospheric phase corruption, thermal noise limits encountered in long integrations (hundreds of hours), and the associated RFI difficulties at the expected frequencies of these redshifts, from ~150 MHz down to ~80 MHz.

Hopefully they will achieve success soon.

Adrian

[JERRY TAYLOR]

Hi Dimitry and Adrian,

You may have already seen this paper, but I thought I would share it just in case you haven't. It claims a record detection of z=1.3 by utilizing gravitational lensing from a foreground galaxy:

https://arxiv.org/pdf/2301.05987

Best regards,
JERRY TAYLOR

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[Dimitry UA3AVR]

Adrian and Jerry, thanks ...

... also hope for high z hydrogen radio detection. The reference to LOFAR project https://arxiv.org/abs/astro-ph/0610596 is from Steven Weinberg's book, Cosmology, 2008. LOFAR was mentioned there as much promising for HI detection with z from 5 to 15.

воскресенье, 2 августа 2026 г. в 18:19:57 UTC+3, JERRY TAYLOR:

[Adrian]

Jerry, 

  Thank you for the reference I was not aware of that record detection.

 It makes sense that gravitational lensing was an important factor in boosting the signal to a detectable level.

Curious if this would be the determining factor for further higher Z detections.

Adrian