Within the LOFAR EoR KSP team, Gaussian Process Regression (GPR) has been used for foreground subtraction from data, to constrain the Neutral Hydrogen 21-cm signal power spectrum from the Epoch of Reionization. To avoid signal loss due to the misestimation of the covariance kernel for the 21-cm signal, we developed a Machine Learning (ML) trained model, by training on a large variety of...
The light-cone (LC) effect arises from the cosmological evolution of the redshifted 21-cm signal along an observer’s line of sight (LoS), which is the frequency axis. It is particularly pronounced during the Epoch of Reionization (EoR) when the mean neutral hydrogen fraction (x_HI) and statistical properties of the universe change rapidly. The 3D power spectrum only quantifies the ergodic part...
The radiations from the first luminous sources drive the fluctuations in the HI 21-cm signal at Cosmic Dawn (CD) via two dominant astrophysical processes i.e. the Ly$\alpha$ coupling and X-ray heating, making this signal highly non-Gaussian. The impact of these processes on the 21-cm signal and its non-Gaussianity vary depending on the properties of these first sources of light. Considering...
The cosmological 21-cm forest, a series of absorption lines in the spectra of high-z radio-loud sources arising from the hyperfine structure of neutral hydrogen residing in the intergalactic medium (IGM), has a potential to be a unique probe of the neutral IGM during the Epoch of Reionization. I will argue that the prospects of detecting the 21-cm forest signal have improved recently because...
The Epoch of Reionization (EoR) remains one of the last frontiers of observational cosmology. The Square Kilometer Array (SKA) is poised to make a preliminary detection of the 21-cm EoR signal within the next decade, and the race will ignite for a confirmation of this detection. One of the most promising avenues is through cross-correlation with galaxies in the same field. I present a...
Line-intensity mapping (LIM) has emerged as a novel technique to probe the large-scale structures in the Universe. It is expected to help probe the Epoch of Reionization, the poorly understood era when the first luminous sources formed in the Universe and reionized the surrounding neutral gas in the IGM. By accumulating the aggregate flux of line emissions such as [C II]$_{158\mu\rm m}$, CO,...
The reionization history of the intergalactic medium (IGM) is not perfectly constrained, although the midpoint is generally accepted to occur near $z\sim8$ and the whole process is likely concluded by $z\sim5.3$. The evolution of the neutral hydrogen fraction $x_\mathrm{HI}$ with redshift is being converged upon through a combination of many observational probes, but one that is particularly...
Multiple-line intensity mappings can trace large-scale structure from now up to reionization, when the first galaxies formed. LIM 3D tomography provides valuable insights into cosmological structure growth, the intergalactic medium, and the properties and environment of ionizing sources. These mappings need updated modeling and inference methods for LIM cosmology because of the large scale and...
We propose a novel method to probe the spectral evolution of the global 21-cm background. Late-time evolution of our universe drives relic backgrounds to be correlated with low-redshift density tracers. This phenomena, the integrated Sachs-Wolfe effect (ISW), has been measured extensively for the cosmic microwave background (CMB) but never for the 21-cm background. We show that the 21-cm...
