Reflections on works by I.S.Shklovsky regarding the nature of radio galaxies

TL;DR

This paper reviews I.S. Shklovsky's extensive 30-year research on the activity and evolution of radio galaxies, highlighting his pioneering ideas and how they compare to modern understanding.

Contribution

It provides a comprehensive overview of Shklovsky's work, including the development of evolutionary diagrams and his theories on gas inflow and jet ejections in radio galaxies.

Findings

Shklovsky's 1962 evolutionary diagram for radio sources.

His hypothesis on gas inflow leading to high-velocity ejections.

Modern perspectives on galactic nucleus activity.

Abstract

The paper is a brief overview of the works by Iosif S. Shklovsky (1916--1985), carried out over almost 30 years (1955--1985), on the nature of activity (primarily in the radio frequency range) in nuclei of some galaxies. Worthy of note is Shklovsky's pioneering work of 1962, in which he made an attempt to consider possible evolutionary tracks of extragalactic radio sources by constructing an analog of the Herzsprung--Russel diagram for stars (radio luminosity at 160 MHz was taken instead of optical luminosity; total radio size at the same frequency, as the other parameter). Later works by other authors are also discussed, where similar diagrams were plotted using a larger observational material. Special attention is paid to the evolution of Shklovsky's views regarding the possible ways of gas getting into radio galaxies' central regions, followed by high-velocity ejections of magnetized plasmons from their nuclei. In his assumptions, Shklovsky was mainly based on the observational data for the properties of the closest radio galaxy, NGC 4486 (Virgo A, M87), which he believed to be the same reference standard for extragalactic radio astronomy as the Crab Nebula for galactic radio astronomy. Shklovsky's approach to the recurrence of the activity phenomenon in galactic nuclei and the one-sided character of radio ejections from them is discussed. Modern views on these issues are also briefly considered.