Relationships of the Active Nucleus, Galaxy, and Environment

Abstract

INTRODUCTION 35 years ago Baade and Minkowski (1954) suggested that a galaxy collision -diagnosed from the peculiar appearance of the parent object and its strong emission lines -is responsible for the strong radiosource CygA. This was the first time that gravitational interactions between galaxies were suggested to trigger nuclear activity. Over the following decades after the detection of the quasars and the gradual realization that quasars, comparable to the Seyfert phenomenon, are events at the nuclei of seemingly isolated galaxies, the collision hypothesis was abandoned. Efforts concentrated on the understanding of the activity as internal processes in the host galaxies, possibly aided by infall of gas from the intergalactic medium (cf. Rees, 1978;Gunn, 1979) .It was only during the last decade after Adams (1977) had noticed from his image-tube survey a "surplus of Seyfert nuclei in disturbed and interacting systems", and later-on when more resolved and deeper quasar imaging became possible that the concepts of triggering interactions gained ground. Presently, the "interaction model" seems to be the dominating paradigm for explaining the origin of nuclear activity in galaxies. In this connection also the wider environment of AGN's and its evolution on cosmical time scales received much attention recently-In this review we concentrate on clues to the origin of AGN's within the interaction picture which we have adopted as working hypothesis. Thus, we shall not much consider here the influence of an already established active nucleus on its galaxy and environment. Consequently, radio jets,galactic winds,and other outflow phenomena, as well as the impact of the active nucleus on the stellar populations of its host galaxy etc. will not be in the main focus of this review talk.Much of the earlier work on the topics covered here is contained in a review article by Balick and Heckman (1982).In the first part we shall consider the environment of QSO's as distant AGN's. Here main aspects and problems of the interaction picture will emerge. In the major second part we concentrate on clues 425 D. Ε. Ο sterbrock and J. S. Miller (eds.), Active Galactic Nuclei, 425-444. © 1989 by the IAU. use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0074180900141580 Downloaded from https://www.cambridge.org/core. IP address: 44.224.250.200, on 05 Jul 2020 at 02:22:25, subject to the Cambridge Core terms ofregarding this picture from observations of nearby AGN's like the Seyfert galaxies. A. QSO's 1. Host galaxies During the last 5 years first by using photographic and later-on CCD imaging convincing evidence has been collected that QSO's are the highluminous nuclei of distant galaxies. The host galaxies of QSO's have been spatially resolved up to redshifts ζ < 0.5, and the continuity of the QSO properties to the lower-level nearby AGN's seems now to be established. Besides being a very difficult task observationally and methodologically the morphological classification of the host galaxies of quasars ha...

QSO Luminosity Functions and Evolution

“…The evolution of the luminosity function is also important in determining the contribution of QSOs to the X-ray background and to the UV ionising field at high redshift. Further clues concerning the evolution of quasars may come from the study of the environment of quasars (see e.g., Yee 1987;Fricke and Kollatschny 1988); the local galaxy density, frequency and type of interactions with other galaxies and the state of the intracluster medium may all affect the formation and fuelling of quasars.…”