Abstract
In this paper, we use analytical methods with some plausible assumptions to develop a mathematical model which may be used to obtain estimate of density of the intergalactic medium (IGM). This relation suggests that the plot of the linear sizes against the bolometric luminosities of the extragalactic radio sources in our sample should be able to furnish us with an estimate of the density of IGM in which the radio sources are domiciled. Moreover, for the purpose of obtaining an empirical relation similar to the theoretical model, we carry out linear regression analysis of linear sizes and luminosities of the 31 radio galaxies in our sample. The regression result shows an empirical relationship between observed source linear sizes and observed bolometric luminosities with slight correlation whose coefficient is 4. Moreover, we compared the theoretical relation and the empirical relation to obtain an estimate of the particle number density of the IGM in which the radio sources are located. The estimate indicates a very low density when compared with the values obtained by authors for the compact steep spectrum (CSS) sources. However, while the linear sizes of the CSS sources are of sub-galactic dimensions – they are located within the interstellar media (ISM) – those of the large extended extragalactic radio sources extend into the intergalactic media. The staggering difference in these obtained densities of IGM and ISM simply supports the general notion that there is a sharp decrease in the density at the IGM–ISM interface. Moreover, using theoretical approach again, with some plausible assumptions, we find another relation which may be used to estimate the ages of extragalactic radio sources. This relation possibly indicates that the plot of the linear sizes against velocities of the radio jets of the radio sources in our sample should be able to supply us with an estimate of the sources’ ages. We find from the simple linear regression analysis of linear sizes and jet velocities of the radio galaxies in our sample, a relation with correlation coefficient given as 4, which is also marginal. Comparison of the two relations – theoretical and the empirical relations – gives an estimate of age of the radio sources. The value shows that these large extended extragalactic radio sources are old sources.
Highlights
Extragalactic radio sources (EGRSs) are those sources with a high ratio of radio to optical emission, commonly defined by the ratio of the two flux densities, ⁄10 [1]
The linear sizes of compact steep spectrum (CSS) sources are of sub-galactic dimensions, m 30 kpc; while those of the larger radio sources extend into the intergalactic media [7, 9, 10]
We find from the simple linear regression analysis of the 31 radio galaxies in our sample, a relation of the form shown in equation (12); with correlation coefficient, d 0.4, which is marginal
Summary
Extragalactic radio sources (EGRSs) are those sources with a high ratio of radio to optical emission, commonly defined by the ratio of the two flux densities,. The lobes contain hotspots believed to be the termination points of the jets [310] They constitute sources whose radio morphologies range from being compact (e.g. compact steep spectrum sources) to the more extended conventional doubles (e.g. radio galaxies) [7,8,9,10]. In this work, we modify the model and use it to estimate value of ambient media density and ages of the larger radio sources. The radio sources used in the analyses are obtained from [11] They are made up of 31 EGRS (radio galaxies) with linear sizes, > 80 kpc. These sources are those whose jets have estimated velocities from [12]
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