Confronting the Chaplygin gas with data: background and perturbed cosmic dynamics
In this paper, we undertake a unified study of background dynamics and cosmological perturbations in the presence of the Chaplygin gas. This is done by first constraining the background cosmological parameters of different Chaplygin gas models with SNIa and $H(z)$ data for detailed statistical analysis of the CG models. Based on the statistical criteria we followed, none of the models has substantial observational support, but we show that the so-called `original' and `extended/generalised' Chaplygin gas models have {\it some observational support} and {\it less observational support}, respectively, whereas the `modified and `modified generalised Chaplygin gas models miss out on the category {\it less observational support}, but cannot be ruled out. The so-called `generalised cosmic Chaplygin gas model, on the other hand, falls under the {\it no observational support} category of the statistical criterion and can be ruled out. The models which are statistically accepted are considered for perturbation level in both theoretical and observational aspects. We also apply the $1+3$ covariant formalism of perturbation theory and derive the evolution equations of the fluctuations in the matter density contrast of the matter-Chaplygin gas system for the models with some or less statistical support. The solutions to these coupled systems of equations are then computed in both short-wavelength and long-wavelength modes. Then feed these observationally restricted parameters into the analysis of cosmological perturbations {to address the growth of density contrast through redshift}. Using the most recent linear growth of the data $f_{σ8}$, CG models are considered to study the linear growth of the structure.