The Compton reflection of X-rays by low temperature electrons has received much attention in the recent past. It is a useful framework for the explanation of some features of the spectra of AGNs and a basic ingredient for understanding the X-ray background spectrum, together with the cosmological evolution of AGN. Since the basic works of Illarionov et al. (1979) and of Lightman et al. (1981), principally based on a semi-analytical approach to the problem, many authors have developed careful Monte Carlo methods to include the effects of the Klein-Nishina cross-section and to extend the study up to the hard X- and γ-ray regions. However, the semianalytical approach has some useful advantages. Firstly it allows us to obtain directly the reflected spectrum in the energy region and at the inclination angle of interest; in addition it may be versatile enough to link with other methods for the computation of the spectrum in the UV and IR regions, where other physical processes are important, but where the X-rays reprocessed by thermal matter may be an important part of the overall luminosity.

The basic assumption of this approach is the separability of the spatial and energy transport problems and of the absorption due to bound-free transitions.

Abstract

One zone chemical evolution models are developed for application to QSO broad emission line regions. The elemental abundances derived from the broad line ratios imply that the gas is highly evolved, with metallicities ranging from ∼1 to ≳ 10 times solar. The short timescales (i.e. ≲ 1 Gyr if qo ≈ ½) and relatively flat initial mass functions (compared to the solar neighbourhood) needed to fit most of the high redshift line ratios are almost identical to the parameters used in one zone models of elliptical galaxies. We conclude that the QSO phenomenon generally follows an episode of rapid star formation, exactly like that expected in massive, young galactic nuclei.

An observed trend in the emission line data suggesting higher metallicities at high redshifts could result from a mass–metallicity–redshift relation among the QSOs. Thus the highest mass QSOs (and/or host galaxies) might form only at high redshifts (e.g. z > 2).

Introduction

The broad emission line spectra of QSOs show that heavy elements are present at redshifts up to nearly z ∼ 5. Therefore some amount of star formation must have occurred before the QSOs ‘turned on’. Unfortunately, the line strengths are not indicative of the overall metal content of the gas, but some of the line ratios are sensitive to the relative abundances (see Ferland & Hamann this volume). The relative abundances can in turn be used to constrain both the metallicity and the past evolution because the elements form by different processes and on different timescales; cf. [2].

Abstract

Two Seyfert 1 galaxies of comparable intrinsic luminosity, NGC 5548 and Markarian 279, have varied by a factor 2 in the optical band within a period of 5 years (1985–1990) during which both have been frequently observed. The large amplitude of the long-term variations reveals evidence that the profile of the broad emission lines depends on the luminosity of the line itself, in the sense that the asymmetry of the lines is stronger when the objects are brighter. This indicates that the structure of the broad line region in these two sources is stable on time scales of 5 years, and that their transfer functions are illumination-dependent in at least part of the radial velocity space. The effect, however, is absent in other, lower luminosity Seyfert 1 galaxies.

Introduction

The technique of reverberation mapping described by Blandford & McKee (1982) has been applied successfully in recent years to derive the transfer function (TF) of the broad line region (BLR) of well-monitored Seyfert 1 galaxies (e.g. Krolik et al. 1991). Until now the common assumption has been that the shape of the TF does not depend on the illumination of the BLR: this implies that if the continuum of a source were constant, the resulting broad lines would have the same profile irrespective of their intensity. The data presented in this paper, however, indicate that the broad lines of two Seyfert 1 galaxies, Markarian (Mkn) 279 and NGC 5548, display different characteristic profiles at different intensities, and therefore that the respective TFs have illumination-dependent shapes in at least part of the radial velocity range.

Abstract

We present results from an analysis of Hα, [OIII] images and long slit spectroscopy of the Seyfert 2 galaxy NGC5953. These show that the nucleus is extended in the northeast direction and surrounded by a vigorous burst of recent star formation.

Introduction

Some interacting Seyfert galaxies show strong circumnuclear emission associated with recent star formation, and one good example of these objects is NGC 5953. This Sa galaxy has a Seyfert 2 nucleus and is in interaction with the late type Scd galaxy NGC 5954 which has a LINER type nucleus, shows distorted spiral arms and is located 44″ to the northeast of NGC 5953.

The radio continuum map at 1.4 GHz shows a diffuse structure over the main body of the galaxy and an enhanced extended component NE of the nucleus. There is a local maximum at p.a. 90°, 5” from the nucleus (Jenkins 1984); this component has been identified with a supergiant HII region (Rafanelli et al., 1990)

We present narrow band images in Hα, [OIII]λ5007 and the nearby continuum, that were obtained with the 4.2m William Herschel Telescope, using the Taurus II box in imaging mode with the f/4 camera. The spatial resolution was 0.27″/pixel. In addition we obtained long-slit spectroscopy with the IDS spectrograph at the 2.5m Isaac Newton Telescope. We used an EEV CCD detector with a spatial resolution of 0.6″/pixel, covering the spectral regions 3300–5200 Å and 5000–6900 Å. A slit of width 1.5″ was oriented in the position angle 44°.

Abstract

We apply the binary black hole model to explain the wiggles in the milliarcsec radio jet of the superluminal quasar 1928+738 (4C73.18) observed with VLBI at 1.3 cm wavelength by Hummel et al. (1992). The period and amplitude of the wiggles can be explained as due to the orbital motion of a binary black hole with mass of order 108 solar masses, mass ratio larger than 0.1 and orbital radius ∼ 1016 cm. The jet's inclination to the line of sight should be small, confirming the standard interpretation of superluminal motion and one-sidedness as due to relativistic motion in a direction close to the line of sight. The small orbital radius suggests that the binary has been losing a significant amount of orbital energy during the last 107 years, possibly by interaction with the matter which is flowing through the active galactic nucleus.

Introduction

Galaxy mergers must have been a common phenomenon especially during the collapse and virialisation of rich groups and clusters of galaxies. These mergers lead to the formation of massive binary black holes in galactic nuclei if black holes of 107−9M⊙ are formed in the nuclei of most bright galaxies at redshifts of about 2. A massive binary black hole (MBBH) may manifest itself by Lens-Thirring precession of a jet emitted along the spin axis of one of the holes (Begelman et al. 1980, hereafter BBR).

Abstract

We present evidence for changes in the transfer function of the broad line region (BLR) in NGC 3516 on time scales of a couple of months. If this occurs in most AGN, it would mean a serious complicating factor for mapping the BLR by reverberation methods. Furthermore, the Hβ profile in this object shows a time-variable dip at the same velocity shift as the strong absorption in CIV λ1550. A corresponding feature is not present in Hα. The question addressed is whether the Hβ dip is absorption or a dip between two emission peaks. These results are part of the LAG project: during the first five months in 1990, a sample of 6 Seyfert-1 galaxies and 2 QSO's were monitored spectroscopically and photometrically. Significant line-profile changes were found in the lower luminosity objects in the sample. The higher luminosity objects displayed continuum variations only.

The time variable transfer function in NGC 3516

In this section we will show that the transfer function of the BLR in NGC 3516 changed significantly over a time scale of several months. This observation could have a profound impact on the use of reverberation mapping as a means to map the structure of the BLR, because it is one of the basic assumptions of reverberation mapping that the transfer function does not change during the experiment.

Abstract

We review the evidence that ejected radio material plays a fundamental role in the formation and kinematics of the Narrow Line region and the extended emission line regions associated with radio jets in radio galaxies and QSO's. In Seyfert galaxies, the key observation is the existence of high-velocity (several hundred km s−1 from the systemic velocity of the galaxy) emission line components which are found systematically closer to the nucleus that the radio emission peaks. We describe how this result can be explained with a high speed bowshock model. In radio galaxies, the strong shock created by the jet results in a surrounding hot cocoon of gas expanding away from the jet axis. These expanding cocoons are visible in the form of double velocity structure in high resolution optical spectra and have now been detected in 3C120, 3C 171, 3C405 and 3C265. The velocity separation between the components can be as high as several thousand km s−1 We briefly discuss how these cocoons can be used to verify the relativisic beaming hypothesis in systems with strong one-sided jets.

Introduction

Extended emission line regions (EELR) closely aligned with the radio structure have been found in Seyferts [20] and radio galaxies at both low [3] and high redshift [10]. The physical conditions and kinematics of these EELR provide a probe of both the radiation field of the AGN and the role played by ejected material in exciting the emission [13].

Abstract

Magnetic forces seem likely to play the dominant role in both the acceleration and initial collimation of relativistic jets in AGNs. I describe recent developments in the theory of hydromagnetic jets and winds.

Introduction

Hydromagnetic propulsion as a mechanism for accelerating jets has become attractive largely through a process of elimination. Other mechanisms, such as acceleration by gas or radiation pressure, have been examined and found inadequate. The observational case for relativistic flow velocities, on both pc and kpc scales, continues to mount (see, e.g., and for recent reviews). Models involving acceleration by radiation pressure would have to be stretched to extremes in order to account for the Lorentz factors ∼ 2 – 10 which are needed to explain most instances of onesidedness and superluminal motion. Losses due to catastrophic cooling place even more severe constraints on acceleration by gas pressure. Recent observations of “intra-day” radio variability, may require Lorentz factors as high as ∼ 100 if catastrophic Compton losses are to be avoided.

Magmetic propulsion has other attractive features besides the ability to produce the high speeds indicated by observations. Chief among these is the tendency of magnetically driven flows to “self-collimate” due to the development of a predominantly toroidal magnetic field. Thus, it may not be necessary to invoke a “funnel” or external confining medium to explain the collimation of jets.

The Seyfert 1 galaxy NGC5548 has been monitored between 1988 December and 1989 October in the optical by an international collaboration (Peterson et al., 1991). Parallel to the optical monitoring, this galaxy was observed every 4 days with the IUE-satellite from Dec. to Aug. (Clavel et al., 1991). The internal calibration of the spectra was done by scaling with respect to narrow forbidden lines.

The optical emission lines Hα, Hβ, HeI5876, and HeII4686 show the same variability pattern as the UV continuum, the Lyα, and CIV1548 lines, but with different delays for the various lines (Fig. 1a — d) (Dietrich, Kollatschny, et al., 1992). We estimated the extent of the broad line region for different lines by cross-correlating the UV-continuum and the emission lines. For the Hα and Hβ lines we got lags of 17 and 19 days respectively. The helium lines originate closer to the central continuum source, as indicated by delays of 7 days (HeII4686) and 11 days (HeI5876).

In Figure 2a,b we have plotted the temporal evolution of the difference spectra of Hα and Hβ for several epochs with respect to that epoch when the galaxy was in the minimum state. The full width at zero intensity (FWZI) remained constant. This indicates a turbulent velocity field in the broad-line region of NGC5548. Furthermore, a blue component (vblue ≈ −2000kms−1) is visible in addition to the central component. This blue component varies independently and with a different amplitude than the central component (Kollatschny and Dietrich, 1991).

Introduction

The existence of microvariability at optical wavelengths has been clearly demonstrated for BL Lacertae objects by a number of groups during the past several years (Miller & Carini 1991, Carini & Miller 1992, Wagner et al. 1991). However, in no instance has the nature of the microvariability been investigated when a blazar was near a minimum in brightness in its long-term variability. Thus, the blazar AO 0235+164 was selected to be monitored with the goal of determining whether or not rapid variations are present when the object is near its minimum brightness level, based on its known historical variability.

Observations

The observations of AO 0235+164 reported here were obtained with the 42-inch telescope at Lowell Observatory equipped with a direct CCD camera. The observations were made through an R filter with an RCA CCD. Repeated exposures of typically 300 seconds were obtained for the star field containing AO 0235+164 and several standard stars. These standard stars, located on the same CCD frame as A0 0235+164, provided comparisons for use in the data reduction process. The observations were reduced using the method of Howell & Jacoby (1986). Each exposure is processed through an aperture photometry routine which reduces the data as if it were produced by a multi-star photometer. Differential magnitudes can then be computed for any pair of stars on the frame.

Abstract

Recent work on the quasar luminosity function at optical and X-ray wavelengths is reviewed. It is shown that the evolution of the quasar luminosity function in these regimes is marked by a strong and approximately similar power law increase in luminosity, L ∝ (1 + z)3±0.5, between the present epoch and z ∼ 2. At z > 2, a slow-down in the rate of quasar evolution is witnessed in both regimes with possible evidence for a decrease in the space density of quasars being seen amongst optically faint (MB > −27) QSOs at z > 3.5.

Introduction

The quasar luminosity function (LF) is one of the most fundamental statistics relating to the quasar population. Estimates of the quasar LF and its evolution with redshift are normally obtained from the statistical analysis of large unbiased quasar surveys with complete spectroscopic identification. As such, the rapid increase in the number of such surveys in recent years, particularly in the optical and X-ray regimes, has led to a dramatic improvement in our knowledge of the quasar LF and its evolution. The purpose of this review is to describe the current observational status of the quasar LF in the optical (4400Å) and X-ray (∼ 2keV ≡ 6.2Å) regimes.

The Optical Luminosity Function

As a result of the recent improvement in quasar statistics at B > 20, it has become increasingly clear (Koo 1983, Marshall 1987, Boyle et al. 1988, Koo & Kron 1988) that the low redshift (z < 3) quasar optical LF (OLF) exhibits a significant break in its power law slope at faint absolute magnitudes.

Introduction

The intense X–ray emission of AGN (active galactic nuclei) can heat the gas in these objects to high temperatures, driving a wind from regions in which the thermal velocity is comparable to or greater than the escape velocity (Begelman et al. 1983). Other mechanisms, such as heating due to dissipation of magnetic fields, or acceleration by rotating magnetic fields or radiation pressure, can also produce winds in AGN; thus, X–ray heated winds may be considered to be the minimum required by observation. These winds are important both because they can alter the accretion rate onto the central object by extracting mass, and because they provide important diagnostics of the distribution and dynamics of gas in AGN (Begelman and McKee 1983).

The nature of the wind is determined by the geometry of the gas relative to the source of the X–rays. The variability of the X–ray emission in AGN indicates that the source of the emission is compact (e.g., Turner and Pounds 1988). The gas may be distributed around this compact source in several possible ways: First, it could be in an accretion disk, although direct observational evidence for this assumption is lacking at present; by contrast, there is good evidence for accretion disks in many binary X–ray sources in the Galaxy. A wind will be driven from an accretion disk either if the disk flares (as it does in the standard α disk—Shakura and Sunyaev 1973) or if the source of the X–rays is above the disk (as in Compton reflection models—Fabian, this volume).