Raghunath Ghara

21-cm signal from cosmic dawn - II: Imprints of the light-cone effects

Details of various unknown physical processes during the cosmic dawn and the epoch of reionization can be extracted from observations of the redshifted 21-cm signal. These observations, however, will be affected by the evolution of the signal along the line-of-sight. We model this light-cone effect by post-processing a dark matter N body simulation with a 1-D radiative transfer code. We find that the effect is much stronger and dramatic in presence of inhomogeneous heating and Lyα coupling compared to that where these processes are not accounted for. One finds increase (decrease) in the coeval power spectrum up to a factor of 3 (0.6) at large scales (k � 0.05Mpc 1 ), though these numbers are highly dependent on the source model. Consequently, the peak and trough-like features in the evolution of the large-scale power spectrum can be smoothed out to a large extent if the width of the frequency bands used in the experiment is large. We argue that it is important to account for the light-cone effect for any 21-cm signal prediction during cosmic dawn.

21-cm signature of the first sources in the Universe: prospects of detection with SKA

Currently several low-frequency experiments are being planned to study the nature of the first stars using the redshifted 21-cm signal from the cosmic dawn and epoch of reionization. Using a one-dimensional radiative transfer code, we model the 21-cm signal pattern around the early sources for different source models, i.e., the metal-free Population III (PopIII) stars, primordial galaxies consisting of Population II (PopII) stars, mini-QSOs and high-mass X-ray binaries (HMXBs). We investigate the detectability of these sources by comparing the 21-cm visibility signal with the system noise appropriate for a telescope like the SKA1-low. Upon integrating the visibility around a typical source over all baselines and over a frequency interval of 16 MHz, we find that it will be possible to make a

Prediction of the 21-cm signal from reionization: comparison between 3D and 1D radiative transfer schemes

\sim 9-\sigma

Line-of-Sight Anisotropies in the Cosmic Dawn and Epoch of Reionization 21-cm Power Spectrum

detection of the isolated sources like PopII galaxies, mini-QSOs and HMXBs at

Probing Individual Sources during Reionization and Cosmic Dawn using Square Kilometre Array HI 21-cm Observations

z \sim 15

Optimal identification of H ii regions during reionization in 21-cm observations

with the SKA1-low in 1000 hours. The exact value of the signal to noise ratio (SNR) will depend on the source properties, in particular on the mass and age of the source and the escape fraction of ionizing photons. The predicted SNR decreases with increasing redshift. We provide simple scaling laws to estimate the SNR for different values of the parameters which characterize the source and the surrounding medium. We also argue that it will be possible to achieve a SNR

Measuring the reionization 21 cm fluctuations using clustering wedges

\sim 9

Modelling the 21-cm Signal from the Epoch of Reionization and Cosmic Dawn

even in the presence of the astrophysical foregrounds by subtracting out the frequency-independent component of the observed signal. These calculations will be useful in planning 21-cm observations to detect the first sources.

21 cm signal from cosmic dawn: imprints of spin temperature fluctuations and peculiar velocities

Three-dimensional radiative transfer simulations of the epoch of reionization can produce realistic results, but are computationally expensive. On the other hand, simulations relying on one-dimensi ...

Imaging the redshifted 21-cm pattern around the first sources during the cosmic dawn using the SKA

The line-of-sight direction in the redshifted 21-cm signal coming from the cosmic dawn and the epoch of reionization is quite unique in many ways compared to any other cosmological signal. Different unique effects, such as the evolution history of the signal, non-linear peculiar velocities of the matter etc. will imprint their signature along the line-of-sight axis of the observed signal. One of the major goals of the future SKA-LOW radio interferometer is to observe the cosmic dawn and the epoch of reionization through this 21-cm signal. It is thus important to understand how these various effects affect the signal for its actual detection and proper interpretation. For more than one and half decades, various groups in India have been actively trying to understand and quantify the different line-of-sight effects that are present in this signal through analytical models and simulations. In many ways the importance of this sub-field under 21-cm cosmology have been identified, highlighted and pushed forward by the Indian community. In this article, we briefly describe their contribution and implication of these effects in the context of the future surveys of the cosmic dawn and the epoch of reionization that will be conducted by the SKA-LOW.