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06-03-2020
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Improved upper limits on the 21-cm signal power spectrum of neutral hydrogen at z ā‰ˆ 9.1 from LOFAR

Submitter: Florent Mertens
Description: Low-frequency observations of the redshifted 21cm line promise to open a new window onto the first billion years of cosmic history. It will allow us to directly study the astrophysical processes occurring during the Epoch of Reionization, the era that saw the first stars galaxies and black holes heating and ionizing the Universe. Detecting the feeble 21 cm signal is however extremely challenging. The LOFAR Epoch of Reionization project has recently made another important step towards this detection.

In a new publication, the project presented the deepest upper limit on the 21 cm signal power spectra at redshift z ~ 9.1, using 141 hours of LOFAR observation of the North Celestial Pole (NCP). The analysis includes significant improvements in calibration, notably in handling direction-dependent effects, and improvements in our foregrounds mitigation and power-spectra extraction methods, leading to a significantly deeper limit on the 21 cm signal compared to our previous analysis (Patil et al. 2017).

The left plot shows the LOFAR-HBA Stokes I continuum images (134ā€“146 MHz) of the NCP field. The right plot shows the current best upper limits of several 21-cm Epoch of Reionization experiments. The new LOFAR upper limit is the deepest observed at redshift 9 and is an improvement by a factor 8 in power compared to the previously reported upper limit. The team is currently busy implementing new improvements in the processing pipeline with the aim to reach the level predicted by theoretical models. This effort is also critical to ensure the success of future observation of the Cosmic Dawn and Epoch of Reionization with the SKA. In an accompanying publication, the team also attempted to constrain the state of the Inter-Galactic Medium at this distant era.

Arxiv Links:
Improved upper limits on the 21-cm signal power spectrum of neutral hydrogen at zā‰ˆ9.1 from LOFAR
Constraining the intergalactic medium at zā‰ˆ 9.1 using LOFAR Epoch of Reionization observations
Copyright: The LOFAR-EoR project
 
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