International Astronomy and Astrophysics Research Journal

In this work, we use statistical methods of analyses to find effects of the intergalactic medium (IGM) and interstellar medium (ISM) of some extragalactic radio sources on dark energy. We carry out linear regression analysis of observed source linear sizes (D) of the more extended radio quasars against their corresponding observed redshifts (Z) in our sample. Also, we carry out similar analysis on the observed linear sizes of compact steep spectrum (CSS) quasars against their corresponding observed redshifts. Results of the regression indicate that if we take D to be distance between any two positions in the IGM/ISM, then cosmic evolution shows an inverse power-law function with the magnitude of the distance between the two positions according to the relation, \((1+z) \sim D^{-\psi}\); where \(\psi=0.6\) and 0.4 for the more extended quasars and CSS quasars respectively. Since “a higher redshift implies an earlier epoch”, and redshift has a direct dependence on expansion velocity between any two points in space, the results of the analyses simply suggest that at earlier epoch, the expansion rate of the universe is higher. Our results also indicate that the effect of cosmic evolution in the extended quasars is more than the effect in the CSS quasars \({ (i. e. } \left.D_{z(E G R Q)}>D_{z(\operatorname{css} Q)}\right)\). Since the linear sizes of the extended radio-loud quasars are projected into the IGM, while the linear sizes of the CSS radio-loud quasars are confined within their individual host galaxies, the result \(\left(D_{z(E G R Q)}>D_{z(\operatorname{cSS} Q)}\right)\) can be interpreted to mean that cosmic evolution shows greater effect in the IGM (i.e. more rarefied medium) than in the ISM (i.e. less rarefied medium). Hence, from the results of the analyses, we may state that if dark energy is defined as the intrinsic tendency of vacuum (or free space) to increase in volume, then the inconsistency in \(D_{z(E G R Q)}\) and \(D_{z(CSSQ)}\) is simply a manifestation of dark energy. Therefore, we may conclusively say that dark energy constitutes a driving parameter behind cosmic evolution. Moreover, we estimate the percentage dilution on dark energy caused by the presence of matter to be \(\approx\) 33%. This implies that if we assume IGM to be approximately an ideal vacuum, then matter present in the ISM offers \(\approx\) 33% dilution effect on dark energy.