arXiv subjects

Kamal Bora

Publications and source records attributed to Kamal Bora.

10 recordsLinked to original sources

arXiv2023

The Hubble constant from galaxy cluster scaling-relation and SNe Ia observations: a consistency test

In this paper, we propose a self-consistent test for a Hubble constant estimate using galaxy cluster and type Ia supernovae (SNe Ia) observations. The approach consists, in a first step, of obtaining the observational value of the galaxy cluster scaling-relation $Y_{SZE}D_{A}^{2}/C_{XSZ}Y_X = C $ by combining the X-Ray and SZ observations of galaxy clusters at low redshifts ($z < 0.1$) from the first {\it Planck mission} all-sky data set ($0.044 \leq z \leq 0.444$), along with SNe Ia observations and making use of the cosmic distance duality relation validity. Then, by considering a flat $Λ$CDM model for $D_A$, the constant $C$ from the first step and the Planck prior on $Ω_M$ parameter, we obtain $H_0$ by using the galaxy cluster data with $z>0.1$. As a result, we obtain $H_0 = 73.014^{+7.435}_{-6.688}$ km/s/Mpc, which represents $9.7\%$ accuracy measurement on the Hubble constant.. We also compare our method with that one where the $C$ parameter is obtained from hydrodynamical simulations of massive galaxy clusters.

astro-ph.CO↗

arXiv2022

A test of the evolution of gas depletion factor in galaxy clusters using strong gravitational lensing systems

In this letter, we discuss a new method to probe the redshift evolution of the gas depletion factor, i.e. the ratio by which the gas mass fraction of galaxy clusters is depleted with respect to the universal mean of baryon fraction. The dataset we use for this purpose consists of 40 gas mass fraction measurements measured at $r_{2500}$ using Chandra X-ray observations, strong gravitational lensing sub-samples obtained from SLOAN Lens ACS + BOSS Emission-line Lens Survey (BELLS) + Strong Legacy Survey SL2S + SLACS. For our analysis, the validity of cosmic distance duality relation is assumed. We find a mildly decreasing trend for the gas depletion factor as a function of redshift at about 2.7$σ$. This is the first result in literature which does not find a constant gas depletion factor as a function of redshift using gas mass fraction measurements at $r_{2500}$.

astro-ph.CO↗

arXiv2022

A test of the standard dark matter density evolution law using galaxy clusters and cosmic chronometers

In this letter, we implement a test of the standard law for the dark matter density evolution. For this purpose, only a flat universe and the validity of the FRW metric are assumed. A deformed dark matter density evolution law is considered, given by $ρ_c(z) \propto (1+z)^{3+ε}$, and constraints on $ε$ are obtained by using galaxy cluster gas mass fractions, and cosmic chronometers measurements. We find that $ε=0$ within 2$σ$ c.l., in full agreement with other recent analyses.

astro-ph.CO↗

arXiv2021

A search for the variation of speed of light using galaxy cluster gas mass fraction measurements

In this paper, we implement a new method to test the invariance of the speed of light ($c$) as a function of redshift, by combining the measurements of galaxy cluster gas mass fraction, $H(z)$ from cosmic chronometers, and Type-Ia supernovae (SNe Ia). In our analyses, we consider both a constant depletion factor (which corresponds to the ratio by which the cluster gas mass fraction is depleted with respect to the universal baryonic mean) and one varying with redshift. We also consider the influence of different $H_0$ estimates on our results. We look for a variation of $c$, given by $c(z)=c_0(1+c_1z)$. We find a degeneracy between our final results on $c$ variation and the assumptions on the gas mass fraction depletion factor. Most of our analyses indicate negligible variation of the speed of light.

astro-ph.CO↗

arXiv2021

Galaxy clusters, cosmic chronometers and the Einstein equivalence principle

The Einstein equivalence principle in the electromagnetic sector can be violated in modifications of gravity theory generated by a multiplicative coupling of a scalar field to the electromagnetic Lagrangian. In such theories, deviations of the standard result for the cosmic distance duality relation, and a variation of the fine structure constant are expected and are unequivocally intertwined. In this paper, we search for these possible cosmological signatures by using galaxy cluster gas mass fraction measurements and cosmic chronometers. No significant departure from general relativity is found regardless of our assumptions about cosmic curvature or a possible depletion factor evolution in cluster measurements.

astro-ph.CO↗

arXiv2021

Probing the time variation of fine structure constant using galaxy clusters and quintessence model

We explore a possible time variation of the fine structure constant ($α\equiv e^2/\hbar c$) using the Sunyaev-Zel'dovich effect measurements of galaxy clusters along with their X-ray observations. Specifically, the ratio of the integrated Compto-ionization parameter $Y_{SZ}D_A^2$ and its X-ray counterpart $Y_X$ is used as an observable to constrain the bounds on the variation of $α$. Considering the violation of cosmic distance duality relation, this ratio depends on the fine structure constant as $\sim α^3$. We use the quintessence model to provide the origin of $α$ time variation. In order to give a robust test on $α$ variation, two galaxy cluster samples, the 61 clusters provided by the Planck collaboration and the 58 clusters detected by the South Pole Telescope, are collected for analysis. Their X-ray observations are given by the XMM-Newton survey. Our results give $ζ=-0.203^{+0.101}_{-0.099}$ for the Planck sample and $ζ=-0.043^{+0.165}_{-0.148}$ for the SPT sample, indicating that $α$ is constant with redshift within $3σ$ and $1σ$ for the two samples, respectively.

astro-ph.CO↗

arXiv2021

Probing the dark matter density evolution law with large scale structures

We propose a new method to explore a possible departure from the standard time evolution law for the dark matter density. We looked for a violation of this law by using a deformed evolution law, given by $ρ_c(z) \propto (1+z)^{3+ε}$, and then constrain $ε$. The dataset used for this purpose consists of Strong Gravitational Lensing data obtained from SLOAN Lens ACS, BOSS Emission-line Lens Survey, Strong Legacy Survey SL2S, and SLACS; along with galaxy cluster X-ray gas mass fraction measurements obtained using the Chandra Telescope. Our analyses show that $ε$ is consistent with zero within 1 $σ$ c.l., but the current dataset cannot rule out with high confidence level interacting models of dark matter and dark energy.

astro-ph.CO↗

arXiv2021

A test of cosmic distance duality relation using SPT-SZ galaxy clusters, Type Ia supernovae, and cosmic chronometers

We carry out a test of the cosmic distance duality relation using a sample of 52 SPT-SZ clusters, along with X-ray measurements from XMM-Newton. To carry out this test, we need an estimate of the luminosity distance ($D_L$) at the redshift of the cluster. For this purpose, we use three independent methods: directly using $D_L$ from the closest Type Ia Supernovae from the Union 2.1 sample, non-parametric reconstruction of $D_L$ using the same Union 2.1 sample, and finally using $H(z)$ measurements from cosmic chronometers and reconstructing $D_L$ using Gaussian Process regression. We use four different functions to characterize the deviations from CDDR. All our results for these ($4 \times 3$) analyses are consistent with CDDR to within 1$σ$.

astro-ph.CO↗

arXiv2021

A model-independent test of the evolution of gas depletion factor for SPT-SZ and Planck ESZ clusters

The gas mass fraction in galaxy clusters has been widely used to determine cosmological parameters. This method assumes that the ratio of the cluster gas mass fraction to the cosmic baryon fraction ($γ(z)$) is constant as a function of redshift. In this work, we look for a time evolution of $γ(z)$ at $R_{500}$ by using both the SPT-SZ and Planck Early SZ (ESZ) cluster data, in a model-independent fashion without any explicit dependence on the underlying cosmology. For this calculation, we use a non-parametric functional form for the Hubble parameter obtained from Gaussian Process regression using cosmic chronometers. We parameterize $γ(z)$ as: $γ(z)= γ_0(1+γ_1 z)$ to constrain the redshift evolution. We find contradictory results between both the samples. For SPT-SZ, $γ(z)$ decreases as a function of redshift (at more than 5$σ$), whereas a positive trend with redshift is found for Planck ESZ data (at more than 4$σ$). We however find that the $γ_1$ values for a subset of SPT-SZ and Planck ESZ clusters between the same redshift interval agree to within $1σ$. When we allow for a dependence on the halo mass in the evolution of the gas depletion factor, the $4-5σ$ discrepancy reduces to $2σ$.

astro-ph.CO↗

arXiv2020

Constraints on variation of fine structure constant from joint SPT-SZ and XMM-Newton observations

We search for a variation of the electromagnetic fine structure constant ($α\equiv e^2/\hbar c$) using a sample of 58 SZ selected clusters in the redshift range ($0.2<z<1.5$) detected by the South Pole Telescope, along with X-ray measurements using the XMM-Newton observatory. We use the ratio of the integrated SZ Compto-ionization to its X-ray counterpart as our observable for this search. We first obtain a model-independent constraint on $α$ of about 0.7%, using the fact that the aforementioned ratio is constant as a function of redshift. We then look for a logarithmic dependence of $α$ as a function of redshift: $Δα/α= -γ\ln(1+z)$, as this is predicted by runaway dilaton models. We find that $γ$ = $-0.046 \pm 0.1$, which indicates that there is no logarithmic variation of $α$ as a function of redshift. We also search for a dipole variation of the fine structure constant using the same cluster sample. We do not find any evidence for such a spatial variation.

astro-ph.CO↗