FIELD GALAXIES MARKARIAN GALAXIES OPTICALLY SELECTED^ QUASARS (LOCAL! KVKRT MF.rRS A/1 INI S-mf—8648 THE SEYFERT GALAXY POPULATION a radio survey; luminosity functions; related objects THE SEYFERT GALAXY POPULATION a radio survey; luminosity functions; related objects proefschrift ter verkrijging van de graad van Doctor in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit te Leiden, op gezag van de Rector Magnificus Dr. AAH. Kassenaar, hoogleraar in de Faculteit der Geneeskunde, volgens besluit van het College van Dekanen te verdedigen op maandag 14 juni 1982 te klokke 14.15 uur door Evert Johan Alexander Meurs geboren te Amsterdam in 1950 Sterrewacht Leiden 1982 Beugelsdijk Leiden B.V. r Promotor: Prof. Dr. H. van der Laan Referenten: Prof. Dr. H.C. van de Hulst Dr. A.G. de Bruyn Voor mijn noeder, in herinnering, en voor Wouter TABLE OF CONTENTS CHAPTER I INTRODUCTION AND SYNOPSIS page 1. Seyfert galaxies 2. Contents of this thesis CHAPTER II OPTICAL POSITIONS OF SEYFERT GALAXIES 15 1. Introduction 2. Accurate Optical Positions of Seyfert Galaxies A.S.Wilson and E.J.A. Meurs, 1978, As iron.As trophys. Suppl.Ser. 33_,407 3. Further measurements CHAPTER III A RADIO SURVEY OF SEYFERT GALAXIES 25 1. A 1415 MHz Survey of Seyfert and Related Galaxies-II E.J.A. Meurs and A.S. Wilson, 1981, Astron.Astrophys. Suppl.Ser. 45,99 2. A 14)5 MHz Survey of Seyfert and Related Galaxies-III (In collaboration with A.S. Wilson.) CHAPTER IV LUMINOSITY FUNCTIONS OF SEYFERT GALAXIES 57 1. Introduction 2. Observational data 3. The optical luminosity function of Seyfert galaxies 4. The radio luminosity function of Seyfert galaxies 5. Conclusions CHAPTER V STUDIES OF RELATED OBJECTS 107 1. Radio Observations at 1.415 GHz of Four Optically Bright Quasars (In collaboration with H.R. de Ruiter.) 2. On the identification of the high-latitude X-ray source 2A1219+305 A. 3. Wilson, M.J. Ward, D.J. Axon, M. Elvis, E.J.A. Meurs, 1979, Mm.Not. R.A.S. 187,109 (continued) r 3. VBLUW Photometry of the Seyfert Galaxy NGC 1566 A.M. van Genderen and E.J.A. Meurs3 1981, Astron.Aatrophys. 96,78 SAMENVATTING 133 CURRICULUM VITAE 135 NAWOORD 136 Front cover: A comparison of the optical luminosity functions of four probably related categories of extragalactic objects (chapter IV, figure 5). Back cover: Characteristic antenna pattern pertaining to the radio observations reported in chapter III.l. CHAPTER I. INTRODUCTION AND SYNOPSIS 1. Seyfert galaxies. 1.1. Definition and tvj>es. The galaxies that are observed in the universe show a variety of forms, ranging from apparently rather dull elliptical systems, via flat systems in which spiral patterns are seen in the light distribution, to very irregular objects. In the past two decades galaxies have been studied in increasing detail, and the observations were extended to other regimes of the spectrum besides the optical region. Different components of galaxies were recognized, of which the galactic nuclei deserve special interest here. Many such nuclei appeared to be very prominent constituents in certain categories of galaxies, observed at various frequencies. The discovery of strong radio emission associated with the centres of elliptical galaxies played an important role in turning general interest towards the study of galactic nuclei. At that time (the end of the 1950's) also more attention was given to an investigation by Seyfert (1943) of a few spiral galaxies with small, very bright nuclei that show emission line spectra. The emission lines of these galaxies appeared to be very broad, with Doppler widths of the order of 10 km s . Galaxies with such broad emission lines are now called Seyfert galaxies. The bright starlike nuclei sometimes form an explicit, photometric element in the definition of Seyfert galaxies. As there are also galaxies with bright nuclei whose spectra show narrow emission lines, we use here the spectros- copie definition which is rather generally accepted. Implicitly, this photo- metric criterion discriminates between the Seyfert galaxies and the quasars, which can be spectroscopically very similar. A study by De Ruiter (1978) showed convincingly that, for certain combinations of redshift and magnitude difference between nucleus and underlying galaxy, the classification of the object as a galaxy or a quasar is determined by the plate scale. The Seyfert galaxies satisfy the original definition of N-galaxies According to Morgan (1958) these are stellar systems having "small brilliant nuclei super- posed on a considerably fainter background". This definition was sharpened subsequently by Matthews, Morgan and Schmidt (1964) to systems in which the nucleus contributes most of the luminosity of the galaxy. It is often applied to compact radio galaxies with such nuclei. Radio galaxies that in recent years were found to have Seyfert-like spectra received names like broad-line and narrow-line galaxy. Weedman (1977) discusses the operational definition of Seyfert galaxies in a comprehensive review on these objects. The subject is also nicely summarized in Weedman (1979). The optical spectra of Seyferts and radio galaxies are described by Osterbrock (1979). Among the Seyferts, two types have been recognized. The type 1's show the very broad lines that are so characteristic for these objects. The widths are of the order of (several times) 10 km s , and involve the permitted (hydrogen) lines. The forbidden lines are narrower, showing widths of 400 - 800 km s .In the spectra of the type 2's both permitted and forbidden lines have widths of 400 - 800 km s . Galaxies with emission line widths smaller than about 400 km s are then called narrow emission line galaxies. There is not a sharp boundary between type 2 Seyferts and narrow emission line galaxies, although Shuder and Osterbrock (1982) find a better distinction between these galaxies when they use line ratio criteria as well. Much valuable information on Seyfert galaxies and related objects, on observations as well as on interpretations and theories, is found in the conference proceedings edited by Ulfbeck (1978) and Hazard and Mitton (1979). 1.2. Sources of Seyfert galaxies. The Seyfert galaxies and also many narrow emission line galaxies have UV excess in comparison with normal galaxies. Because of this property, the objective prism survey for galaxies with UV excess, conducted by B.E. Markarian at the Byurakan Observatory (references in chapter IV.2.1) provided a large number of emission line galaxies. This material proved to be a rich source of Seyfert galaxies. About two-third of this survey, that comprises in total 1400 objects, has been further investigated spectroscopically, resulting in about 100 Seyferts. There are some other well-known categories in which Seyfert galaxies occur: Arakelian galaxies, Zwicky compact galaxies, Tololo galaxies (see references in Weedman 1977). In recent years a number of Seyferts has been found after their discovery as an X-ray source. 1.3. Observations_of_Seyfert_galaxies. In addition to the general references cited in § 1.1, we mention in this section some useful collections of observational data, partly published after those general references. 10 It has been noted that the classical NGC-Seyferts are ail spiral galaxies (this is not very clear in the case of NGC 1275, but its classification as Seyfert is not clear either). An ir ige-tube survey of a large number of Seyferts (Adams 1977), generally much further away than the NGC Seyferts, showed most of them to be spiral galaxies as well. It would be interesting to have photometric data (optically), pertaining really to the nuclear region of the Seyferts. Attempts have been made to obtain JBV data observing photo-electrically with small apertures (Weedman 1973), or employing short-exposure photographs (Véron 1979). Such data include as yet only a rather small part of ail (Ma:karian) Seyferts. Spectroscopy of Seyfert galaxies was already mentioned in § 1.1. Much information on the spectral energy distribution is contained in the absolute spectrophotometry of De Bruyn and Sargent (1978). A number of IR fluxes are given by Rieke (1978). Compared with normal spiral galaxies, the Seyfert galaxies are strong radio emitters. This is discussed extensively in chapter IV of this thesis, based on observations with the Westerbork Synthesis Radio Telescope (WSRT). Many aspects of their radio properties are discussed by De Bruyn rad Wilson (1978). The observational programs that presently are conducted at the VLA reach a much higher resolution than was achieved with the WSRT. The \ ^A. observations offer the possibility to explore the central regions of Seyferts in considerable detail. Prominent among the VLA results, aptly summarized by Wilson (1982), is the occurrence of small-scale (kpc or less) double-lobed or jetlike structures. A number of Seyferts was detected in X-ray radiation with the Ariel V and Uhuru satellites. A review by Wilson (1979) cf this material contains a wealth of information on the continuous spectra of these galaxies. The Einstein satellite further increased the number of detections (Kriss et al. 1980). 1.4. Natureof th The possible nature of the nuclei of Seyfert galaxies has led to many theories and speculations. The role of a compact object in the very nucleus of these galaxies is generally accepted. The favourite identification for this object is a massive black hole, because it can convert mass with high efficiency into enormous amounts of energy. The fuel that is needed for this central engine is provided by stars and/or gas. Near this very nucleus, within 1 pc, the broad wings of the permitted lines in type 1 Seyferts 1 I are thought to be formed in a region with dense gas. The narrow line region 2 3 is of the order of 10 - 10 pc, presumably the same region with much less dense gas where the radio emission steins from (De Bruyn and Wilson 1978).