Coffee talks
Friday 15/11/2024 @ 11:30, Sala riunioni quarto piano e on-line (meet.google.com/sue-bwvk-axf)
Emilio Ceccotti (INAF-IRA), "Advanced modeling of bright radio sources for LOFAR 21-cm power spectrum analysis: the Cygnus A and 3C196 cases"
Studying the redshifted 21-cm signal emitted by neutral hydrogen during the Epoch of Reionization and Cosmic Dawn is crucial for understanding the physics of the early universe. A key challenge for 21-cm experiments like LOFAR is the contamination from bright foreground sources, which requires accurate spatial and spectral models to reduce residual contamination after their removal. This modeling is essential in scenarios where bright sources are close to the observing direction, such as in the 3C196 field, as well as in situations where they are far from the main field of view, as observed with A-team sources in the North Celestial Pole (NCP) field. In this talk, I present a new, high-resolution model of Cygnus A, the brightest of the A-team sources, obtained from LOFAR-HBA observations. This model improves previous models by incorporating physical spectral information through the forced-spectrum method during multi-frequency deconvolution. I demonstrate how this new model enhances the quality of foreground subtraction and hence has the potential to lower the upper limits on the 21-cm power spectrum from the NCP field. Furthermore, I introduce the first upper limits at z~9 from the 3C196 field, based on a single night of observations with LOFAR-HBA. The modeling challenge here is presented by 3C196, a ~100 Jy source at the center of the field, which helps the calibration but must be meticulously subtracted to minimize its residuals. Using a LOFAR-VLBI model of 3C196 and a new processing pipeline, we achieve promising results that highlight the accuracy and potential of LOFAR for cosmological 21-cm signal observations.