arXiv subjects

Sanjay K. Pandey

Publications and source records attributed to Sanjay K. Pandey.

3 recordsLinked to original sources

arXiv2024

Bullet Cluster: Remarkable Revelations and Enduring Insights -- Part I

This study unveils new insights into the Bullet Cluster through cm-wave observations made with the Australia Telescope Compact Array, focusing on the Sunyaev-Zeldovich Effect (SZE). A novel SZE feature was discovered, distinctively offset from the X-ray brightness peak, challenging conventional associations between such phenomena. The findings, achieved through high-resolution interferometric imaging, reveal complex substructures within the SZE, including significantly displaced components uncorrelated with X-ray, optical, or lensing maps. This deviation underscores the complexity within the cluster's dynamics and suggests that detailed, high-resolution SZE imaging is crucial for understanding the physics of merging clusters. We perform several tests to ensure that one of these novel and unusual features is indeed real, and that the detection of all features in the images is robust. In addition to these displacements, we find several SZE features that are tentatively located at critical boundaries in this merging cluster - these features will be discussed in the next few papers in this series. These observations pave the way for more sophisticated analyses, combining SZE and X-ray data, to decode the evolutionary mysteries of cosmic structures like the Bullet Cluster. We note here that we are discussing only one novel and peculiar feature in the observations of the cluster done in the year 2019. Further observations have revealed more features, which we shall discuss in the next few papers in this series on the Bullet cluster.

astro-ph.CO↗

arXiv2006

Probing the bispectrum at high redshifts using 21 cm HI observations

Observations of fluctuations in the redshifted 21 cm radiation from neautral hydrogen (HI) are perceived to be an important future probe of the universe at high redshifts. Under the assumption that at redshifts z less than 6 (Post-Reionization Era), the HI traces the underlying dark matter with a possible bias, we investigate the possibility of using observations of redshifted 21 cm radiation to detect the bispectrum arising from non-linear gravitational clustering and from non-linear bias. We find that the expected signal is ~ 0.1 mJy at 325 MHz (z=3.4) for the small baselines at the GMRT, the strength being a few times larger at higher frequencies 610 MHz (z=1.3). Further, the magnitude of the signal from the bispectrum is predicted to be comparable to that from the power spectrum, allowing a detection of both in roughly the same integration time. The HI signal is found to be uncorrelated beyond frequency separations of 1.3 MHz whereas the continuum sources of continuum are expected to be correlated across much larger frequencies. This signature can in principle be used to distinguish the HI signal from the contamination. We also consider the possibility of using observations of the bispectrum to determine the linear and quadratic bias parameters of the HI at high redshifts, this having possible implications for theories of galaxy formation.

astro-ph↗

arXiv2005

Probing non-Gaussian features in the HI distribution at the epoch of reionization

The HI distribution at the epoch of reionization (EOR) is largely determined by the sizes and distribution of the ionized regions. In the scenario where the ionized regions have comoving sizes of the order of a few Mpc, the large scale statistical properties of the HI distribution are dominated by the Poisson noise of the discrete ionized regions, and it is highly non-Gaussian. We investigate the possibility of probing reionization by studying these non-Gaussian features using future radio interferometric observations of redshifted 21 cm HI radiation. We develop a formalism relating correlations between the visibilities measured at three different baselines and frequencies to the bispectrum of HI fluctuations. For visibilities at the same frequency, this signal is found to be of the same order as the two visibility correlation which probes the HI power spectrum. For visibilities at different frequencies, we find that the correlations decay within a frequency difference of ~1 MHz. This implies that it is, in principle, straightforward to extract this HI signal from various contaminants which are believed to have a continuum spectra and are expected to be correlated even at large frequency separations.

astro-ph↗