arXiv subjects

Sauraj Bharti

Publications and source records attributed to Sauraj Bharti.

3 recordsLinked to original sources

arXiv2026

Joint Optical-HI mock catalogues and prospects for upcoming HI surveys

Atomic hydrogen (HI) regulates star formation as cold gas fuels star formation. It represents a key phase in the baryon cycle. Redshifted $21$ cm line emission serves as a key tracer for investigating HI in the interstellar medium (ISM) and circumgalactic medium (CGM) in distant galaxies, and enables the study of galaxy evolution. Direct detections of HI are currently limited to $z \leq 0.4$ due to the inherently weak $21$ cm emission line. Ongoing and upcoming large radio surveys aim to detect $21$ cm emission from galaxies up to $z \gtrsim 1$. We present a novel approach for creating optical-HI joint mock catalogues for upcoming SKA precursor surveys: MIGHTEE-HI, LADUMA and WALLABY. Incorporation of optical properties along with HI makes these mock catalogues a powerful tool for making predictions for surveys and provides a benchmark for exploring the HI science (e.g., conditional HIMF and optical-to-HI scaling relations) expected from these surveys. As a case study, we show the use of the joint catalogues for predicting the expected outcome of stacking detection for average HI mass in galaxies that are below the threshold for direct detection. We show that combining stacking observations with only the number of direct detections puts a strong constraint on the HI mass function. We also show that this can be done separately for parts of the color-magnitude diagram for galaxies, enabling a fine grained study of galaxy evolution. This may be used to set priors for the full determination of the HI mass function.

astro-ph.GA↗

arXiv2025

Gravitational lensing of 21 cm HI signal: detection prospects at z ~ 1 with uGMRT in galaxy cluster lenses

The atomic hydrogen HI content of galaxies is intimately related to star formation and galaxy evolution through the baryon cycle, which involves processes such as accretion, feedback, outflows, and gas recycling. While probing the HI gas over cosmic time has improved our understanding, direct HI detection with the redshifted 21 cm line is essentially limited to $z\lesssim 0.42$. Detections beyond this redshift are based on stacking to obtain average HI mass of galaxy populations. Gravitational lensing by the cluster lenses enhances the HI signal and can extend the redshift limit further. In this work, we describe simulations of HI lensing in cluster lenses. We explore the feasibility of detecting strongly lensed HI emission from background galaxies using known $50$ cluster lenses within the uGMRT sky coverage. We demonstrate that certain clusters offer a strong likelihood of HI detection. We also investigate how strong lensing distorts the HI spectral lines. The shape of the HI signal in these lensing models provides useful information and can be used in optimising signal extraction in blind and targeted HI surveys. We find that blind detection of HI signal from galaxies in the redshift range up to $1.58$ requires more than a few hundred hours of observations of individual clusters with the uGMRT. Detecting HI emission in galaxies with strong optical lensing seems promising, with a $5σ$ detection potential in less than 50 hours for Abell 370 and 75 hours for Abell 1703 using the uGMRT.

astro-ph.CO↗

arXiv2023

Upcoming SKA precursor surveys and sensitivity to HI mass function

We describe a simulation for the distribution of galaxies focusing on the atomic Hydrogen content. We aim to make predictions for surveys of galaxies using the redshifted 21 cm line emission. We take the expected distribution of HI masses, circular velocities, sizes of galaxies and orientations into account for this simulation. We use the sensitivity of ASKAP and MeeKAT radio telescopes to estimate the number of detections of HI galaxies in upcoming surveys. We validate our simulation with earlier estimates carried out by using some of these considerations. We show that unlike earlier simulations that take some of the factors into account, the predicted number of galaxies and their distribution across masses changes significantly when all of these are accounted for. We describe our predictions for the MIGHTEE-HI and WALLABY surveys for blind detection of galaxies using the redshifted 21 cm radiation. We study the dependence of the predicted number of detections on the HI mass function. We also describe our future plans for improving the simulation.

astro-ph.CO↗