arXiv subjects

Md Rasel Hossen

Publications and source records attributed to Md Rasel Hossen.

5 recordsLinked to original sources

arXiv2026

Local environmental dependence on weak-lensing shear statistics

Despite the assumption that an ideal FLRW observer is not dependent on the local environment, observations are biased by the positions of the observers due to the matter correlations in the large-scale structure (LSS) of the universe. The variation of the mass distribution of the LSS of the universe implies that observers residing in different locations may suffer bias in their measurements when they look at the images of distant galaxies. Here, we assess the influence of the local environment on weak gravitational lensing (WL) shear statistics in the context of relativistic $N$-body code, \texttt{gevolution}. We derive numerical constraints on the cosmological parameters from the WL shear angular power spectrum and comment on the local environment's influence on WL shear. We find tighter constraints on the parameter $Ω_\mathrm{m}$ above redshift $z$ = 0.2, which implies over this redshift the local environment's impact is minor. We also investigate the bispectrum and conclude that on average the impact of the local environment on $f_{\rm NL}$ (a measure of non-Gaussianities) is minimal and consistent with zero effect. However, we find that within the assembly of all possible observers/locations, there will also be a few that could infer the parameter $f_{\rm NL}$ of the order 10. These results could thus be used to estimate the uncertainty in the inference of cosmological parameters such as $f_{\rm NL}$ based on WL shear bispectrum and thus may have implications for future surveys requiring precision at the percent level.

astro-ph.CO↗

arXiv2026

Tracing Cosmological Signature with Doppler Lensing: Insights from Cosmological Simulations

Doppler lensing, a relativistic effect resulting from the peculiar velocities of galaxies along the line of sight, provides insight into the large-scale structure of the Universe. Relativistic simulations are essential for modeling Doppler lensing because they incorporate gravity and motion in spacetime. We compare two relativistic $N$-body simulation frameworks, $\texttt{GEVOLUTION}$ and $\texttt{SCREENING}$, to calculate Doppler lensing convergence in cosmic voids of different sizes and halos of different masses. Our analysis reveals scale-dependent performance: $\texttt{SCREENING}$ shows larger differences in small voids (radius range: 15--25 Mpc/h) with a mean absolute relative difference of 38.5\%, due to linearized dynamics failing in nonlinear regimes. Medium voids (25--35 Mpc/h) show better agreement (9.5\% mean difference). For large voids (35--45 Mpc/h), $\texttt{SCREENING}$ exhibits intermediate differences (16.9\% mean difference) with central instabilities. Moreover, our Doppler convergence analysis with massive halos ($10^{11.5}$--$10^{14} {~h^{-1}\mathrm{M}_\odot}$) demonstrates excellent consistency (1.6--3.6\% mean difference). These findings provide clear guidance for simulation choice: $\texttt{GEVOLUTION}$ is recommended for precision studies critical to $Λ$CDM or modified gravity tests, while $\texttt{SCREENING}$ offers a computationally efficient alternative for relativistic treatments with large catalogs of voids and halos, assisting future astrophysical surveys.

astro-ph.CO↗

arXiv2022

Ringing the universe with cosmic emptiness: void properties through a combined analysis of stacked weak gravitational and Doppler lensing

An essential aspect of cosmic voids is that these underdense regions provide complementary information about the properties of our Universe. Unlike dense regions, voids are avoided by matter and are less contaminated by baryonic processes. The first step to understanding the properties of cosmic voids is to correctly infer their mass profiles. In the literature, various techniques have been implemented. In this paper, we review them and implement a new technique that is based on Doppler lensing. We use a relativistic $N$-body code, \textsc{Gevolution}, to generate cosmological mass perturbations and implement a three-dimensional ray-tracing technique, which follows the evolution of a ray-bundles. We focus on the various properties of cosmic voids (e.g. void size function, 2-point correlation function, and the density profile of voids), and compare the results with their universal trends. We show that when weak-lensing is combined with the Doppler lensing we obtain even tighter constraints than weak-lensing alone. We also obtain better agreement between density profiles within central parts of voids inferred from lensing and density profiles inferred from halo tracers. The implication of the result relevant to the ongoing and prospective low-redshift spectroscopic surveys is briefly discussed.

astro-ph.CO↗

arXiv2021

Mapping the cosmic mass distribution with stacked weak gravitational lensing and Doppler lensing

Dark matter halos represent the highest density peaks in the matter distribution. Conversely, cosmic voids are under-dense patches of the universe. Probing the mass distribution of the universe requires various approaches, including weak gravitational lensing that subtly modifies the shape of distant sources, and Doppler lensing that changes the apparent size and magnitude of objects due to peculiar velocities. In this work, we adopt both gravitational and Doppler lensing effects to study the underlying matter distribution in and around cosmic voids/halos. We use the relativistic $N$-body code \texttt{gevolution}, to generate the mass perturbations and develop a new ray-tracing code that relies on the design of the ray bundle method. We consider three categories of halo masses and void radii, and extract the cosmological information by stacking weak-lensing and Doppler lensing signals around voids/halos. The results of this paper show that the most optimal strategy that combines both gravitational and Doppler lensing effects to map the mass distribution should focus on the redshift range $z\approx 0.3-0.4$. The recommendation of this paper is that future spectroscopic surveys should focus on these redshifts and utilise the gravitational and Doppler lensing techniques to extract information about underlying matter distribution across the cosmic web, especially inside cosmic voids. This could provide a complimentary cosmological analysis for ongoing or future low-redshift spectroscopic surveys.

astro-ph.CO↗

arXiv2021

The density distributions of cosmic structures: impact of the local environment on weak-lensing convergence

Whilst the underlying assumption of the Friedman-Lemaître-Robertson-Walker (FLRW) cosmological model is that matter is homogeneously distributed throughout the universe, gravitational influences over the life of the universe have resulted in mass clustered on a range of scales. Hence we expect that, in our inhomogeneous universe, the view of an observer will be influenced by the location and local environment. Here we analyse the one-point probability distribution functions and angular power spectra of weak-lensing (WL) convergence and magnification numerically to investigate the influence of our local environment on WL statistics in relativistic $N$-body simulations. To achieve this, we numerically solve the null geodesic equations which describe the propagation of light bundles backwards in time from today, and develop a ray-tracing algorithm, and from these calculate various WL properties. Our findings demonstrate how cosmological observations of large-scale structure through WL can be impacted by the locality of the observer. We also calculate the constraints on the cosmological parameters as a function of redshift from the theoretical and numerical study of the angular power spectrum of WL convergence. This study concludes the minimal redshift for the constraint on the parameter $Ω_m$ ($H_0$) is $z \sim 0.2$ $(z \sim 0.6 )$ beyond which the local environment's effect is negligible and the data from WL surveys are more meaningful above that redshift. The outcomes of this study will have direct consequences for future surveys, where percent-level-precision is necessary.

astro-ph.CO↗