This contribution considers the consequences of an active nucleus (AGN) inside a galaxy with a nuclear starburst. General arguments suggest that many AGN generate supersonic winds (Smith 1993a, see also Voit et al. 1993) with velocities vw ∼ 0.1 vo.1c, and the interaction of such a wind with a surrounding starburst is considered below. The large number of quasars indicate that some starburst galaxies should contain the remnant black holes of these “dead” AGN. Even if fueled by only a small amount of gas, the resulting AGN wind can have a significant effect on starburst hydrodynamics.

Note that it is unlikely that a black hole (BH) and subsequent AGN could form due to accretion during the lifetime (10τ10 Myr) of the starburst. Since Eddington limited accretion has a timescale of ∼ 500 Myr, a seed black hole would have to accrete at a rate greater than ∼ 50/τ10 times the Eddington rate to grow substantially.

Mass and energy injection by the supernovae and stellar winds of the starburst will form an outflowing wind. A nuclear wind produced by the AGN will evacuate the central region out to the radius where the mass flux injected by the starburst activity is greater than the mass flux in the nuclear wind. At this point the nuclear wind becomes mass loaded, subsonic, and will merge into the developing starburst wind (Smith 1993b). For a uniform starburst the nuclear wind (with kinetic luminosity will become mass loaded at a radius is the starburst mass injection rate, parameterized as the supernova rate times the mass injected per supernova (including stellar winds).

ABSTRACT

Using new high-resolution imaging at optical wavelengths, we study the morphology of the inner kpc of two barred spirals, NGC 4321 and NGC 4314. In the case of NGC 4321, we present evidence for the existence of a nested bar and a nested spiral structure. In the case of NGC 4314, the inner star formation activity is not organized in spiral arms, but has a ring-like appearance. The role of large scale bars and of possible nested bar structure in the fueling of nuclear starbursts is briefly discussed.

INTRODUCTION

The need to dissipate angular momentum of material flowing into the central region of a galaxy is one of the problems in the process of fueling active galactic nuclei (AGN). Non-axisymmetric potentials are capable of achieving an efficient dissipation of angular momentum, and bars may well trigger the nuclear activity of galaxies (see e.g. Simkin et al. 1980). Shlosman et al. (1989) proposed a mechanism where a set of nested bars can play an important role in this process. “Bars within bars”, possibly of a similar kind to those proposed by Shlosman et al., have been observed in a number of galaxies (see e.g. de Vaucouleurs 1974; Friedli and Pfenniger 1993 and references therein).

We show here preliminary results from an imaging study of two barred spiral galaxies which show a mild form of nuclear activity: a (circum-)nuclear starburst. These galaxies, NGC 4314 and NGC 4321, are well-known cases where strong formation of massive stars takes place in a region within about 1 kpc in radius from the center (see e.g. Pogge 1989).

ABSTRACT

Observational evidence for the existence of bars in the central parts of Seyfert galaxies Mkn 744, Mkn 573, and NGC 4151 is presented.

INTRODUCTION

Afanasiev (1981) investigated rotation curves of 28 Seyfert galaxies and found local maxima at distances 0.5–2 kpc from the centers in 20 objects. The rotation velocity declined with the increasing distance from the local maximum more rapidly than for the Keplerian law. This suggests a possibility of development of Kelvin-Helmholtz instability leading to essential turbulization of the circumnuclear disk (global gas instability in the disk) (Morozov 1979). Observed solid body rotation, from the center to the local maximum, indicates a possible presence of bars in the centers of Sy s.

GAS MOTION FEATURES IN THE BAR'S REGION

Gaseous disk in the region of the bar is thinner than the latter, has lower chaotic velocities and rotates faster than the bar Ωd > Ωb (Fridman 1987). If the radius R1, where the relative linear velocity ΔVR reaches the sound speed in the gaseous disk ΔVR = (Ωd – Ωb)R > Vs, is within the bar region (Rb), then a shock may arise for R1 < Rb. The shock front then will be observed on the rear side of the bar with respect to the direction of rotation, if the disk and the bar rotate in the same direction. Depending on the ΔVR value, either strong or weak shocks will be observed in the optical band (mainly in the forbidden lines) as linear structures.

ABSTRACT

Recent observations of non-circular cold gas motions in the central 100 pc — 1 kpc regions of galaxies are summarized, with an emphasis on relating the observed local motions to net inflow and outflow rates.

INTRODUCTION

Non-circular gas motions have been detected in many galaxies, providing empirical evidence that radial gas flows continue to affect the evolution of galaxies long after the initial epoch of galaxy formation. This paper reviews observations of non-circular motions of the cold (molecular and atomic) gas in the 100 pc – 1 kpc circumnuclear regions of disk galaxies. This is typically the region of galaxies where bulges begin to dominate the potential, where rotation curves change from steeply rising to flat, and where circumnuclear starbursts occur. Molecular gas is generally the dominant phase of the interstellar medium by mass in the central regions of gas-rich disk galaxies, and for this reason many of the observations discussed in this review are of CO or other tracers of molecular gas. The weakness of HI emission in circumnuclear regions, and the related difficulty of determining HI kinematics at high resolution, make HI results less common but valuable. Although on average inflowing gas is probably colder than outflowing gas, there are examples of both outflowing molecular gas and inflowing ionized gas.

The relationships between the observed local non-circular motions and the net radial flow rates vary considerably, and in several important cases the net flow rates are much smaller than the local non-circular motions.

ABSTRACT

VIA H I observations of the interacting pair IC 2163/NGC 2207 are presented. The velocity and structural anomalies of IC 2163 agree with predictions of N-body galaxy encounter simulations if IC 2163 recently underwent a strong, prograde, in-plane encounter with NGC 2207. The velocity disturbances in NGC 2207 suggest that the main tidal force on NGC 2207 was perpendicular to the disk of NGC 2207.

INTRODUCTION

The spiral galaxies IC 2163 and NGC 2207, shown in Figure 1, are involved in a close tidal encounter. IC 2163 has an ocular shape (an eye-shaped central oval with a sharp apex at each end), intense star formation along the eyelid regions, and a double-parallel arm structure on the side opposite its companion, NGC 2207.

The optical morphology of IC 2163 is consistent with N-body simulations by Elmegreen et al (1991) if IC 2163 underwent a strong, in-plane, prograde encounter with NGC 2207 during the last half-rotation. One component of the double arm is the usual tidal tail; the other component is produced by rapid streaming of tidally perturbed stars and gas from the companion (western) side of the galaxy. The simulations predict a velocity difference of 50 to 100 kms-1 between the two components of the double arm and large streaming motions along the oval.

Using the VLA, we made H I observations of this galaxy pair to study the early stages of post-encounter evolution and to look for the velocity anomalies predicted by the numerical simulations.

ABSTRACT

We are studying the optical, radio, and X-ray morphologies of interacting galaxies in which at least one member is also an active galaxy. Deformed gas distributions are seen in galaxies that also show optical evidence of tidal deformation, indicating significant gas redistribution in these interacting systems, thereby providing compelling evidence for a causal connection between tidal and nuclear activity in “interactive” galaxies.

THE INTERACTION-ACTIVITY CONNECTION

Stockton (1990) and Heckman (1990) have reviewed the wealth of evidence indicating that galaxy interactions are somehow related to the generation of starburst and AGN activity in galactic nuclei. For example, a large fraction of low-luminosity radio and active galaxies have nearby companions or show evidence for a recent gravitational encounter (e.g., MacKenty 1989). In an optical study of galaxies selected on the basis that they all contain well defined radio jets, it was found that almost half of the sample consists of pairs of elliptical galaxies (Colina and Pérez-Fournon 1990a, b). Many of these low-luminosity radio galaxies with companions (e.g., 3C31, 3C278, and 3C449) show a well defined distorted radio jet structure at the VLA scale with an S– or C-shaped morphology. We are currently studying these systems across many wavebands (optical, radio, and X-ray) in an attempt to model the observed morphologies in each case and thereby constrain the various properties of the system (orbital parameters, jet parameters, and hot gas distribution, respectively). These system constraints will hopefully offer some physical insight into the interaction-activity connection.

Broad-Line Radio Galaxies (BLRG) are the most extreme species of AGN regarding line width and structure of their optical emission line spectra. The FWZI amounts to Δv ≃ 35,000 km s-1 for some objects. Furthermore, the broad line profiles are more structured than these of Seyfert galaxies and show often double hump features (Chen, Halpern, and Filippenko 1989; Halpern 1990; Veilleux and Zheng 1991). The detailed analysis of the line profile variations of these AGN provides a powerful tool to get information about fundamental parameters of the Broad-Line Region (BLR) like size, geometry and especially the kinematics of the line emitting gas (Robinson, Pérez, and Binette 1990; Welsh and Home 1991).

In 1989 we started a monitoring campaign of line profile variations of Broad-Line Radio Galaxies at Calar Alto Observatory/Spain on time scales of weeks to years. In the following we present some examples of emission line profile variations of BLRGs we are studying.

3C390.3 is a well known BLRG with prominent double-peaked Hα emission line profile. The spectra shown in Figure 1 were taken in October 89 and August 92. The line flux was scaled with respect to the narrow forbidden [OIII]λλ4959, 5007 and [OI]λ6300 emission lines. The corresponding difference spectrum is displayed at the bottom of Figure 1. The Hα and the Hβ line profiles show a double-peak structure in the difference spectrum. The humps are separated by Δv ≃ 9,000 km s-1. A component at vrel = 4600 km s-1 described by Veilleux and Zheng (1991) is not visible for these epochs.

ABSTRACT

Results of 3D numerical simulations of a two-component self-gravitating galactic disk embedded in a ‘live’ halo are presented. The pure stellar disk is chosen to be globally unstable and forms a stellar bar. A ‘seed’ black hole (BH) of 5 x 107 M⊙ with an ‘accretion’ radius of 20 pc is placed at the center. The details on the numerical method are given in Shlosman and Heller (these proceedings and references therein). Here we study the effects of star formation (SF) which is introduced when (1) the gas is Jeans unstable; and (2) the gas density exceeds ∼ 100 M⊙ pc-3. The formed massive stars account for the gas heating by means of line-driven winds and by supernovae, assuming an efficiency of kinetic-to-thermal energy conversion of a few percent. Models with and without SF are compared and only the robust features are emphasized.

We find that the SF has induced angular momentum loss by the gas and has increased the radial inflow by a factor < 3. We also find that (1) SF is concentrated at the apocenters of the gaseous circulation in the bar and in the nuclear region; (2) the nuclear starburst phase appears to be very luminous (quasar-like) and episodic; and (3) the nuclear starburst phase correlates with the catastrophic growth of the BH. Without the pre-existing BH, the gas at the center (few x 100 pc) becomes dynamically unstable and forms a gaseous bar which drives a further inflow. The gaseous bar may fission into a massive cloud binary system.

ABSTRACT

We have performed broad-band CCD imaging of a sample of 24 low luminosity radio galaxies containing radio jets. Their optical properties, photometric parameters, and their local environments have been studied and compared with other samples of radio galaxies.

Radio galaxies can be classified in two groups, powerful radio galaxies (PRG, with total power P≥ 1025 W Hz-1 at 1.4 GHz) and low luminosity radio galaxies (LLRG, with total power P≤ 1025 W Hz-1 at 1.4 GHz), both from their radio as well as their optical properties. Among the main works that allowed to establish the differences in line emission, photometric structure, and environment between the two classes we should mention those by Hine and Longair (1979), Heckman et al. (1985, 1986), Lilly and Prestage (1987), Owen and Laing (1989), and Smith and Heckman (1989a, b). PRG usually show Fanaroff-Riley type II radio morphology (Fanaroff and Riley 1974), strong optical emission lines, and photometric structure similar to normal ellipticals. LLRG generally show FR I morphology, weak emission lines or pure absorption line spectra, and optical luminosity and light profiles similar to bright cluster galaxies.

One feature that powerful and low luminosity radio galaxies have in common is the morphological evidence of ongoing or past interaction/merging processes in these systems (Heckman et al. 1986; Lilly and Prestage 1987; Smith and Heckman 1989a, b; Colina and Pérez-Fournon 1990a, b; González-Serrano and Pérez-Fournon 1992 and references therein). However the indications of interaction of each class appear in different form.

ABSTRACT

We describe a program of N-body simulations of clusters of galaxies. Results concerning merging histories and the kinematic properties of multiple nuclei are presented.

THE MODELS

We have completed nine N-body evolutions of models containing 50 galaxies using a total of N = 4 × 104 particles. The models are fully self-consistent in that each galaxy is represented as an extended structure containing many particles and the total gravitational potential arises from the particles alone. The evolutions are carried out with a direct N-body code based on the Barnes and Hut (1986) TREE algorithm for computing the gravitational potential; it is the code developed by Lars Hernquist (1987, 1990) with some modifications (Bode, Cohn, and Lugger 1993).

For all the models, 10% of the particles are ‘luminous’ and the rest represent ‘dark’ matter; the former are given a smaller softening length than the latter. The dark matter is apportioned between galaxy halos and a smoothly distributed cluster background. The percentage of mass initially in this intra-cluster background, β, is varied from 50% to 90%.

The initial mass distribution of the galaxies follows a Schechter function. For β = 50%, the smallest galaxy contains 125 particles and the largest 3500 particles. Galaxies are given a core-halo structure by identifying the most bound particles in each galaxy as luminous. Since the total amount of mass in the cluster is the same for all models, increasing β has the effect of removing mass from the galaxy halos and distributing it through the cluster.

ABSTRACT

Using the VLA in A-configuration we have obtained λ21cm absorption spectra of 12 Seyfert galaxies with bright, extended continuum radio emission. Currently, we have completed the data reduction for three galaxies: NGC 1068, Markarian 3, and NGC 3079. No absorption is detected in Mrk 3, but multiple and broad absorption lines were detected in NGC 1068 and NGC 3079. Here we present the preliminary analysis for these galaxies.

NGC 1068

The radio continuum emission from NGC 1068 is dominated by a 13″ radio triple extending SW–NE (e.g., Wilson and Ulvestad 1987). We have detected HI absorption over the entire SW radio lobe and the southern half of the central source. Three kinematically distinct regions are apparent: the radio nucleus, the linear radio structure 1–2″ SW of the nucleus (the SW “jet”), and the SW radio lobe. Using the technique of Dickey, Brinks, and Puche (1992), we extracted optical depth spectra for each of these regions (Fig. 1). Broad (FWHM = 130 ± 25 km s-1), double absorption lines are present in the nuclear region. Adopting usys(HI)= 1137 km s-1 (de Vaucouleurs et al. 1991, RC3), the lines are offset by +55 ± 11 and -283 ±11 km s-1. We suspect that these lines may arise in a region of rapid rotation and streaming near the active nucleus. In the SW “jet” multiple absorption lines centered at usys are apparent. Since this region lies along the 2.2 μm stellar bar (Thronson et al. 1989), these multiple absorption lines may be due to gas streaming in the bar potential.

ABSTRACT

We present a new model for the dynamics of molecular clouds in the innermost ≈ 200 pc from the Galactic Center. Our analysis allows us to determine the characteristic parameters of the accretion disk as well as the positions of individual clouds with respect to the Galactic Center. Finally, we show that the results are in good agreement with independent determinations of the same parameters and discuss a physical mechanism that allows for the theoretical understanding of these parameters.

OVERVIEW

We assume that the dynamics of accretion disks in the innermost ≈ 200 pc from the Galactic Center (GC) can be modelled in the framework of an accretion disk description. The two parameters that mainly determine the structure of the disk are the radial mass flow rate through the disk (Ṁ) and the dynamical viscosity (v). For a pair of these two parameters, one can calculate the radial velocities (us) in the disk with respect to the GC and, consequently, the observable quantity ux, the radial velocity with respect to the observer (of course, after applying all the relevant corrections). In an iterative process, with this method, we determine the pair (Ṁ, v) that gives the best agreement between the observed and modelled values of vx. Having found such a solution, we also determined the location of the individual clouds with respect to the GC. Thus, this technique allows us also to construct a map of the distribution of molecular clouds close to the GC. In the next section, we summarize our ansatz for describing the accretion disk.

ABSTRACT

We calculated the orbital evolution of stars due to interaction with an accretion disk around a massive black hole in a galactic nucleus. After circularization the radius of a stellar orbit with initial inclination i to the disk shrinks by a factor 4/(1 + cos i)2 before it settles in the plane of the accretion disk. Next, we calculate the rate at which stars from the star cluster around the hole are captured by a standard Shakura-Sunyaev disk. We find that the majority of captured stars are on retrograde orbits. These stars may reach a small separation from the hole before settling in the disk. AGN with M ∼ 106 M⊙ and Ṁ = MEdd are likely to have stars on inclined orbits with small separation from the hole, i.e. just outside the tidal disruption radius. Observational effects will be most conspicuous in low luminosity AGN.

EVOLUTION OF STAR ORBIT

The pre- and post-impact velocities v and v1 can be calculated from conservation of momentum: m*v + Δmw = (m*, + Δm)v1, where Δm is the mass swept up by the star and w is the velocity of the accretion disk at the impact point. These three equations together with the requirement that the pre– and post–impact positions are the same, provide a set of four relations between the old and new orbital parameters. It is possible to find explicit expressions for the changes in the orbital parameters by linearizing these equations (Roos and Kaastra 1993, in preparation).

ABSTRACT

Galaxy bars can be important triggering agents for star formation, radial gas flows, and nuclear activity. This paper reviews the observational evidence for bar-induced star formation and gas redistribution in spiral galaxies. Specific topics include the global star formation rates in barred vs normal galaxies, the spatial distribution and abundances of star forming regions in barred systems, and circumnuclear hotspots.

INTRODUCTION

Barred galaxies present one of the clearest cases of mass-transfer induced activity, and as such are valuable laboratories for understanding the triggering of starbursts and nuclear activity in a broader context. As reviewed by Athanassoula elsewhere in this volume, hydrodynamic simulations suggest that bars can trigger a wide range of phenomena, including large-scale gas compression, star formation, and radial transport of gas into the nuclear region (also see Sellwood and Wilkinson 1993).

This paper reviews the observational evidence for bar-induced star formation and circumnuclear activity. I begin by discussing the integrated properties of barred vs normal spirals, based on surveys in Hα, radio continuum, and the infrared (section 2). Section 3 summarizes the star formation properties of individual barred systems, with emphasis on the bars themselves and their surrounding disks. In section 4 I discuss the circumnuclear “hotspot” star formation regions, which are probably the most distinctive signatures of bar-induced activity. I conclude with a summary of outstanding questions and important areas for future work.

INTEGRATED PROPERTIES OF BARRED VS NORMAL SPIRALS

The first systematic comparisons of the global properties of barred and normal galaxies were based on radio continuum surveys (Cameron 1971; Dressel and Condon 1978; Dressel 1979; Heckman 1980).

ABSTRACT

The idea that Seyfert nuclear activity might be fueled by material inflow induced by a perturbing companion has been fashionable for over a decade. However, the recent literature on the prevalence of Seyfert galaxy companions, is confusing and somewhat contradictory. To clarify this we have constructed a statistical profile of Seyfert galaxy companions in the CfA ZCAT. We use a random sampling technique to estimate the statistical significance of the observed excess of Seyfert companions relative to the rate of pairing found in non-active galaxies. We find the excess of close pairs for Seyfert galaxies to be highly significant.

RESULTS

More than a decade ago, the morphological similarities between patterns seen in Seyfert galaxies and those produced by gravitational forcing led to the suggestion that Seyfert activity might be fueled by material inflow induced by either a central bar or a perturbing companion (Simkin, Su, and Schwarz 1980). The recent literature on the prevalence of Seyfert galaxy companions, however, is somewhat confusing and, at initial glance, contradictory (cf. the extensive review in Osterbrock 1991). Most authors have attributed their disparate conclusions to observational selection effects, (op. cit.). The problems arise because to obtain a valid statistical profile of the non-AGN “control” galaxies requires either an enormous observational effort or a series of ad hoc assumptions which differ with each study.

An alternative approach to this statistical problem is to draw the Seyfert galaxy sample from a larger catalog of galaxies all subject to the same measurement errors and selection effects. With this approach, the non-Seyfert galaxies provide the statistical profile necessary for interpretation.

ABSTRACT

I describe studies of the incidence of nuclear activity and star-formation rates for galaxies in two paired samples, as functions of the encounter direction and kinematic properties of the disturbed disk. One sample, designed to test star-formation diagnostics, is a geometrically derived subset of the Karachentsev catalog. A separate sample, of paired Seyferts, is used to search for common kinematic characteristics among interactiontriggered AGN. Both starbursts and Seyfert nuclei occur with about equal frequency in direct and retrograde encounters. Nuclear and disk star formation are correlated with the form of the velocity curve, and with the normalized amplitude of velocity disturbance in the disk. Seyfert nuclei in pairs show a high fraction of galaxies with large solid-body regions in the rotation curves. Such kinematic properties are associated with higher then normal star-formation rates in the K-pair spirals (but not the highest). For both AGN and starformation processes, the theoretical scheme most nearly accounting for the observations gives a prominent role to a Toomre-style disk instability on large scales, perhaps driving more local processes such as cloud collisions or pressure-induced cloud collapse. Including kinematic information offers a more refined way to identify externally-triggered phenomena than do disturbed morphology or presence of companions alone.