つくば宇宙理論コロキウム

第47回

Low frequency radio observation with MWA and SKA Low exploring the cosmic dawn and epoch of reionization

吉浦 伸太郎 氏

国立天文台


要旨
The Square Kilometre Array (SKA) Low and Mid, the world's largest radio telescopes, are currently under construction in Australia and South Africa. Covering frequency ranges of 50–350 MHz for SKA Low and 350 MHz–15.4 GHz for SKA Mid, the SKA will enable a wide range of scientific studies, leveraging its exceptional sensitivity and imaging capabilities. One of the primary science goals of SKA Low is to explore the Epoch of Reionization (EoR) and Cosmic Dawn (CD). The key observable is the 21 cm line from neutral hydrogen, which evolves during the EoR and CD as the first stars and galaxies modulate the state of intergalactic hydrogen gas. The redshifted 21 cm signal, observed at frequencies below 200 MHz, provides insights into the distribution of neutral hydrogen and allows SKA Low to reveal the birth of the first stars, the presence of faint galaxies, the ionization history, and cosmology. However, detecting the 21 cm signal is challenging due to strong foreground contamination, primarily from Galactic and extragalactic synchrotron emission, which is more than three orders of magnitude brighter than the expected signal. To detect the 21 cm signal, precise instrument calibration and effective foreground mitigation strategies are required. Previous studies have placed upper limits on the 21 cm signal using various telescopes, including the Murchison Widefield Array (MWA), a precursor to SKA Low. We are now conducting analysis of radio signal observed by the MWA at 85MHz for understanding the foreground and systematics and for detecting the 21cm line at the CD. In this colloquium, I will introduce the observation of redshifted 21 cm signal with the MWA and the SKA.
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