On Size Evolution / Radiated Power of Extragalactic Radio Sources and Implication

Abstract

We have applied in this work, statistical methods of analyses to find empirically some effect posed by source expansion on radiated power of extragalactic radio sources. The subclasses of the sources used are radio-loud quasars and radio galaxies. We have done this by carrying out linear regression analyses of observed source angular sizes \((\theta)\) of the quasars against their respective observed redshifts \((z)\) ; as well as, observed source luminosities \((P)\) against their respective observed redshifts. For the quasars, result indicates that with good correlation coefficient \((r \approx 0.5)\) observed angular size shows an inverse relationship with observed redshift, and is given by \((\theta \sim(1+z)^{-1.9}\). For the galaxies, the result indicates similar trend; we obtain \theta \sim(1+z)^{-3.7}, where \(r \approx 0.6\) (which is also a good correlation). Moreover, on the \(P-z\) plane, we obtain a direct relationship given by \(P \sim(1+z)^{0.04}\) for the quasars; where \(r \approx 0.8\) (which is a good correlation). However, for the galaxies, luminosity/redshift relationship is poor \(\text { (with } r \approx 0.1 \text { ) }\). This poor correlation may possibly have stemmed from lack of observation of galaxies at high redshifts unlike observation of their quasar counterparts. The \(\theta / z\) relationships for the quasars and the galaxies simply indicate positive source size evolution with time. However, the converse is the case for \(P / Z\) relationship – it shows negative source luminosity evolution with time. These results suggestively indicate that extragalactic radio sources, though small scaled at earlier epoch, were more powerful sources than what they are at present epoch. Their luminosity/angular size relation is given by \(P \sim \theta^{-0.01}\). Therefore, conclusively the results suggestively indicate that the mechanisms of size evolution of these sources simply bring about diminution effect on their radiated power.