Fredagskollokvium: Katrine Glasscock, Institute of Theoretical Astrophysics, University of Oslo

Title:
«Radio silence? Reaching the Epoch of Reionisation with 21cm measurements»

Abstract:
Radio cosmology today is driven by high-precision instruments like LOFAR, MeerKAT, and HERA, which push 21cm signal limits. So far, there is no direct detection of this highly anticipated neutral hydrogen signal from the Epoch of Reionisation and beyond. The next-generation instrument SKA will be the largest radio interferometric array, enabling high dynamic range radio maps of the 21cm signal and its anisotropies. However, vast data volumes expand radio inference challenges, with foregrounds up to five orders brighter than the signal. Additionally, ARCADE 2 and LWA suggest an anomalous Radio Synchrotron Background (RSB) excess. This excess aligns with CMB radiation at high frequencies but deviates from a blackbody spectrum at lower frequencies, suggesting an additional astrophysical or exotic source. While various explanations have been proposed, such as modified populations of faint extragalactic sources or new physical processes, there is still no consensus on the origin of this potential signal, making the RSB excess an open question in radio cosmology. In this talk, I will present a novel Bayesian formalism based on Gibbs sampling, that can iteratively sample the sky and its covariance. The formalism is based on a visibility response operator, that incorporates all the instrument degrees of freedom. It also automatically deals with any gaps in the data. Better understanding the diffuse foregrounds and anomalous signals will not only improve foreground mitigation for 21cm cosmology, but will also enrich our understanding of radio astronomy and cosmology in general.

Image credits: The Milky Way over the Hydrogen Epoch of Reionization Array (HERA). Credit: HERA / Dara Storer

Venue: Peisestua (room 304), Svein Rosselands hus ( https://www.uio.no/om/finn-fram/omrader/blindern/bl26/)

**All are welcome to join!**

More upcoming seminars:
https://www.mn.uio.no/astro/forskning/aktuelt/arrangementer/gjesteforelesninger-seminarer/fredagskollokvium/2025/

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