ABSTRACT

Preliminary results of a search for gas transfer between the galaxies in E+S pairs are presented. In the pair considered K542, ionized gas is detected in the nucleus of the elliptical but no gas in the process of being transferred between the two components has been found.

INTRODUCTION

In the past ten years observations of the ionized (Phillips et al. 1986) and HI (Knapp et al. 1985) gas content of early type galaxies have shown that 50-60% of these galaxies contain a modest amount of interstellar gas. On the basis of the H I data, Knapp and coworkers have suggested that the interstellar gas in ellipticals may be of external origin. At least two external sources for the gas have been suggested: the capture of small gas-rich companions and accretion from nearby gas-rich galaxies. Mixed morphology E+S pairs make an ideal laboratory to test the second hypothesis, since the presumed external source for the gas is relatively unambigous. Two possible strategies exist to test the hypothesis, 1) define a sample of E+S pairs and a control sample of isolated ellipticals and compare the global gas content of the two samples, or 2) examine a sample of E+S pairs that are likely candidates to be currently crossfueling and attempt to catch them in the act. We have chosen the second strategy, since optical spectra had already been obtained for several E+S pairs.

ABSTRACT

I briefly discuss several specific issues regarding the possible inter-relationships between starbursts, quasars, and their extranuclear environments. First, I will argue that the case for fueling starbursts from the extranuclear environment is very strong. The luminosities of extreme starbursts are so large that they essentially require the complete conversion of a galaxy's interstellar medium into massive stars within a single dynamical time. Such starbursts should make good local laboratories for studying the processes involved in galaxy (spheroid) formation. Next, I will discuss the recent proposal by Terlevich and Boyle that the population of high-redshift radio-quiet quasars can be understood as the post-starburst-cores of young/proto elliptical galaxies (with no supermassive black holes required), and will argue that it has a serious energetics problem. Finally, I will describe the effects that the mechanical energy released by starbursts (and possibly quasars) has on their gaseous environments.

INTRODUCTION

The subject I have been asked to review — the complex inter-connections between starbursts, quasars, and their surrounding environment — is far too broad in scope to adequately summarize here in its entirety. I will therefore restrict my review to discussing some specific topics, all pertaining in some way to two general issues.

The first general issue concerns the connection between starbursts and quasars. How can we tell starbursts and quasars apart? Is there any causal or evolutionary connection between them? These issues have been recently reviewed by several different authors (Blandford 1992; Filippenko 1993; Heckman 1987, 1991). The second general issue concerns the two-way communication between starbursts or quasars and their environments.

ABSTRACT

The evolution of the gas distribution in a globally unstable galactic disk embedded in a ‘live’ halo is studied numerically on scales ∼ 100 pc –10 kpc. The gas and stars are evolved using a 3D hybrid SPH/N-body code and gravitational interactions are fully accounted for. The gas is assumed to obey the isothermal equation of state with T – 104 K. The effect of a massive object at the disk center is simulated by placing a ‘seed’ black hole (BH) of 5 x 107 M⊙ with an ‘accretion’ radius of 20 pc. Modifications introduced by star formation in the disk are discussed elsewhere (Heller and Shlosman, these proceedings).

We find that the global stability of a stellar disk can be heavily affected by the gas, given that the gas mass fraction fg is high enough and the gas is dissipative. We also find that the rate of radial inflow in disk galaxies is a robust function of global parameters: the inflow is bar-driven for small fg and dynamical friction-driven for largefg. Without star formation the radial inflows lead to (1) domination of the central kpc by a few massive clouds that evolve into a single object via a cloud binary system; and (2) sporadic accretion onto the BH.

ABSTRACT

We have measured the line-of-sight velocity profiles of M32. The major axis velocity profiles are asymmetric, with opposite asymmetry on opposite sides of the nucleus. Existing models for M32 cannot account for these asymmetries. We present new models which assume the distribution function to be of the form f = f(E, Lz). Such models require a central black hole of ∼ 1.8 × 106 M⊙ to fit the observed rotation velocities and velocity dispersions. Without invoking any further free parameters, these models provide a good fit to the observed velocity profile asymmetries.

OBSERVED VELOCITY PROFILES

The presence of a massive black hole has been invoked to match the observed rotation velocities and velocity dispersions at the center of M32 (Tonry 1987; Richstone, Bower and Dressier 1990). Previous studies have assumed the line-of-sight velocity distributions of the stars, henceforth referred to as the velocity profiles, to be Gaussian. We have determined the velocity profile shapes of M32 from high S/N spectra taken with the William Herschel Telescope at La Palma (van der Marel et al. 1993), using the techniques of Rix and White (1992) and van der Marel and Franx (1993). The velocity profiles are asymmetric, with the asymmetry changing sign upon going from one side of the nucleus to the other (see Fig. 1). None of the existing models, in which the local (unprojected) velocity distributions of the stars are assumed to be Gaussian, can reproduce the observed asymmetries of the velocity profiles.

ABSTRACT

Radial gas flows can be induced in a galactic disk by a bar potential, and its implied gravitational torques. All gas inside corotation is driven towards the center, and forms a nuclear ring at the inner Lindblad resonance (ILR). When the mass concentration is high enough, there exists two ILRs, and the existence of periodic orbits perpendicular to the bar makes the gas response to shift in phase with respect to the stellar main bar. This produces a strong torque on the gas, and drives a rapid nuclear gas flow inside ILR. With a more viscous gas, however, a second bar of stars and gas can decouple from the primary one, with a higher pattern speed. In this “bar within bar” configuration, the gas is in phase with the stellar component, and the gravity torques are minimised. The gas inside the second corotation flows slowly inwards. The nuclear bar is relatively long- lived, which explains its frequent occurence in observed barred spirals.

NUCLEAR BARS AND THEIR POSSIBLE INTERPRETATIONS

Bars are the way to redistribute angular momentum in a galaxy, and to reshape the mass distribution. The induced gas flow towards the center is the cause of star-bursts, hot spots in nuclear rings, and may be of nuclear activity. A clue to the detailed mechanisms of the central gas flow is the observation of nuclear bars and central isophote twists. This phenomenon in barred spiral galaxies has been observed for a long time. Already de Vaucouleurs (1974) had noticed bars within bars, and Sandage and Brucato (1979) high surface brightness nuclear bars, as independent entities.

ABSTRACT

We present details of galaxy morphology in the compact group Seyfert's Sextet obtained with the HST-WFC.

INTRODUCTION

Seyfert's Sextet (SS, HCG 79) exhibits one of the highest galaxy surface density enhancements (> 103, Sulentic 1987) outside the core of a rich galaxy cluster. There are convincing signs of interaction between the component galaxies, including: 1) optical evidence of bridges, tails and a common low light level envelope (Sulentic and Lorre 1983), and 2) a distorted distribution of neutral hydrogen (Williams et al. 1991).

HST OBSERVATION AND DECONVOLUTION

SS was observed with the WFC on 12 May 1992. Nine 15-minute exposures were taken with the F439W (B) filter and processed with the standard STScI pipeline. The frames were accurately registered (to within 1 pixel), allowing us to combine them into a single averaged picture. Cosmic rays were removed by ignoring pixels which were significantly (3σ) deviant from the corresponding pixels on other frames.

Deconvolution was performed using both the Richardson-Lucy package bundled in IRAF/STSDAS (refer to the STSDAS User Guide), and the σ-CLEAN algorithm (Keel 1991), optimized to change the point-spread function (PSF) according to position on the chip. PSFs were computed using the Tiny Tim (refer to The Tiny Tim User's Manual) package. A 50 iteration deconvolution was carried out with the Lucy package. After 80,000 iterations with CLEAN the model brightness distribution showed little change. Each of these algorithms presents strong and weak points. Lucy handled very well large structures (low spatial frequencies), such as the halo connecting the galaxies. However, the final brightness distribution seemed to be dependent on the number of iterations used.

ABSTRACT

We use published data for 31 early-type members of binary systems in order to estimate the slope of the (Dnσ) relation. This is considered to be a representation of the Fundamental Plane (FP) for ellipticals. We find a slope for this relation of a = 0.92 ±0.18 when computed with a simple model for the distances. A similar slope has been obtained by others for galaxy groups and it is comparable to values obtained for clusters with a low Abell richness. The scatter of pair values around the FP does not correlate with galaxy properties such as ellipticity, isophotal twisting and total color index. The larger deviations from the (Dnσ) relation tend to involve pairs with smaller projected separations.

INTRODUCTION

Concerns about independence of the FP from environmental conditions have been expressed by Djorgovski et al. (1988), Lucey et al. (1991a, b) and De Carvalho and Djorgovski (1992). On the contrary, Burstein et al. (1990) suggest that the FP does not depend on environment demonstrating, in particular, that the (Dnσ) relation does not depend upon cluster properties.

Isolated binaries represent a different environment from that of a cluster center where galaxies have had time to homogenize. Binary galaxy evolution is driven by a combination of three time scales which are roughly of the same order: the orbital period, the rotational period of the individual galaxies and the burst duration of star formation (SF) triggered by the encounters. Theoretical simulations suggest that they merge rapidly (compared to a Hubble time) into E galaxies, because tidal friction is very efficient.

This book includes contributions to the International Astrophysics Conference on Mass–Tranfer Induced Activity in Galaxies, held at the University of Kentucky, Lexington, on April 26–30, 1993. More than 140 participants from 17 countries attended, compared to 70 planned originally. We feel that such interest was fueled at least in part by the Conference being solely devoted to this fascinating subject.

This Conference was based on a number of review talks which prepared the audience for the follow-up discussion and contributed papers. We aimed at providing a balanced view of the field which by now has become well defined, reaching a certain degree of maturity. Some overlap between different review papers was planned and the careful reader will enjoy sometimes contradictory explanations of the same ‘facts’.

The main question concerning the origin of active galaxies is tantalizingly simple: how does nature remove all but ∼ 10-7 of the angular momentum (in AGNs) initially residing in the gas a few kpc from the center, accomplishing this on the orbital timescale? And how do the nuclear starbursts fit within this picture — as a passive by-product or a major player forcing the gas inwards and/or outwards?

We proceed from ‘inside out’ (in the footsteps of the Creator?) by addressing first the angular momentum transfer within the central parsec. Next, the kinematics and molecular, atomic and ionized gas distributions in the circumnuclear region are reviewed followed by large-scale gas properties in barred and normal disk galaxies and in ellipticals.

ABSTRACT

Rapid optical variations have been detected for the Seyfert 1 galaxy Akn 120 with time scales shorter than an hour. These variations are the most rapid which have been detected for any Seyfert galaxy, and, for the first time, clearly demonstrate that radio-quiet AGNs exhibit the phenomenon of microvariability. This result suggests that these variations are indepentent of the radio properties of these objects and are thus unlikely to be associated with any disturbance in a relativistic jet.

INTRODUCTION

Akn 120 was first identified as a Seyfert galaxy by Arakelian (1975) in a survey of high surface brightness galaxies. It has long been known to exhibit optical variations with time scales ranging from years to days (Miller 1979). In this paper, we report the first results of a program to determine if radio-quiet AGNs exhibit optical variations on time scales much shorter than a day.

OBSERVATIONS

The high time resolution optical observations of Akn 120 reported here were obtained with the 42-inch telescope at Lowell Observatory equipped with a direct CCD camera and an autoguider. The observations were made through a V filter with an RCA CCD. Repeated exposures of 60 seconds were obtained for the star field containing Akn 120 and several comparison stars. These standard stars, located on the same CCD frame as Akn 120 provide comparison stars for use in the data reduction process. The observations were reduced using the method described in Carini and Miller (1992).

INTRODUCTION

A wealth of information has been presented at this conference illustrating the basic theme that large-scale gas inflows can result in the release of large amounts of energy in galactic nuclei by starbursts and by non-thermal processes associated with black hole accretion. Particular attention has been paid to two situations in which such phenomena frequently occur: (1) bar-driven inflows in barred spiral galaxies can lead to gas accumulation and star formation in nuclear rings of ‘hot spots’, and (2) tidal interactions and mergers between galaxies can cause large amounts of gas to fall rapidly into their nuclei and produce luminous starburst and non-thermal activity. Although it is difficult to observe the gas inflows themselves directly, partly because they may be masked by more conspicuous outflows, inflows are commonly predicted by numerical simulations of barred and interacting galaxies, and the success with which these simulations match many of the observed properties of such systems leaves little doubt that inflows occur quite generally whenever a non-axisymmetric gravitational potential is present. Evidence that gas inflows from regions of galactic size are responsible for triggering the most energetic outbursts of activity in galactic nuclei is provided by the fact that in many of the most luminous systems, an amount of molecular gas comparable to the gas content of an entire large spiral galaxy is observed to be concentrated into a small nuclear region only a few hundred parsecs across.

OBSERVATIONS

The MBG survey (Montreal Blue Galaxy) is a spin-off project of the Montreal Cambridge Tololo (MCT) survey of southern subluminous blue stars (Demers et al. 1986). Using a subset of the plate material covering 7000 deg2, with b ≤ -40∘, we pick up all extended UV-bright objects. The analysis of our follow-up spectroscopy has shown that the bulk of our UV-bright candidates consists of H II galaxies or starbursts; the fraction of AGNs being somewhat less than 10% (Coziol et al. 1993). We expect to find ∼ 500 such galaxies, with magnitude B ≤ 15.5.

Recently, we undertook an imaging follow-up of our candidates to determine their morphology and search for clues to the origin of their activity. Our first sample consist of 11 MBG galaxies with strong H II-region like spectra suggesting an intense phase of star formation. Usually, these galaxies also possess relatively hot IRAS color typical of starburst galaxies (Sekiguchi 1987). Using our 1.6m telescope, located on mont Mégantic in Québec, Canada, we obtained CCD images, with BVRI filters. Details of the observations, reductions and analysis will be published elsewhere (Coziol, Barth, and Demers 1993). Following, is a summary of our first results.

We find mostly spiral galaxies with bright nuclear regions. There is a strong tendency to find early type galaxies. Further analysis of the surface photometry reveals that the bursts are located, preferentially, in the circumnuclear region prolonging far into the nucleus. This confirms the earlier spectral classification of our objects, using the excitation diagnostic diagram of [O III]λ5007/Hβ versus [N II]λ6584/Hα, which suggested that MBG objects are mostly starburst nuclei galaxies (see Salzer et al. 1989 for a definition).

NGC 3079 is a remarkable spiral galaxy which exhibits an unusual range of nuclear activity. Viewed edge-on, it harbors a reddened LINER (Low Ionization Nuclear Emission-line Region) that is kinematically complex, with several distinct components of Ha emission. It also contains a compact, flat spectrum nuclear radio source, and shows well-defined, kiloparsec-scale radio lobes of considerable complexity, as well as a smaller loop of Hα+[N II] emission extending approximately along the minor axis of the galaxy. The optical emission lines indicate that gas is outflowing from the nucleus in an energetic, bipolar outflow or “galactic superwind.” Armus et al. (1990) have suggested that this wind is driven by a powerful, central starburst. A number of different lines of evidence — its infrared brightness (measured by IRAS, the extended 10 μm emission, the spatially coincident, circumnuclear molecular gas, and the extremely luminous H2O maser — point to the presence of ongoing, vigorous star formation within the nucleus, in agreement with this idea. However, other authors (e.g., Irwin and Sofue 1992; Filippenko and Sargent 1992) argue that the nuclear activity originates from an AGN, perhaps supplemented by a powerful starburst.

We have obtained ROSAT PSPC observations of NGC 3079 and the adjacent spiral galaxy NGC 3073. Preliminary analysis indicates that X-ray emission from NGC 3079 consists of a point-like source, superposed on lower level emission which is extended by 2.5′ in approximately the same direction as the radio jet, Hα loop, and radio lobes (Figs. 1, 2). The extended emission is roughly coincident with two Hα filaments detected by Heckman et al. (1990), and may consist of either a shell-like or a filled structure.

ABSTRACT

The balance of energy in AGNs and quasars is assessed. It is shown that there is no “energy budget” problem in AGNs and quasars and the covering factor of the broad line region in these objects is around 0.1-0.2 and this does not change with the luminosity.

INTRODUCTION

It has been claimed that there is an “energy budget problem” for some continuum energy distributions (CEDs) used to model the broad line region (BLR) in AGNs and quasars. In this paper the budget of energy in AGNs is assessed from UV and soft X-ray observations.

ENERGY BUDGET

Soft X-ray observations of AGNs were obtained from the ROSAT/PSPC archive (at the University of Leicester, England) and reduced in the standard way (see Gondhalekar et al. 1993 for details). A single power law was found to be adequate to represent the data and the power law index (Γ) is given in Table 1. The details of this analysis will be the subject of a separate publication. The soft X-ray spectra deviate significantly from the (best fit by eye) models of Laor and Netzer (1989) at energies higher than 0.5 keV.

RESULTS

Maffei 2, a nearby SBb pec galaxy behind the Galactic plane, is the site of a nuclear burst of star formation as evidenced by near infrared (Rickard and Harvey 1984, A. J., 89, 1520; Ho et al. 1989, Ap. J., 344, 135), Brackett line (Ho et al. 1990, A. J., 349, 57), and radio continuum emission (Seaquist, et al. 1976, Astr. Ap., 48, 413; Turner and Ho 1993, preprint). Its proximity (∼5 Mpc) and large angular extent (∼10′) make it an ideal candidate for high resolution neutral gas studies which are necessary for understanding the processes driving the nuclear starburst.

The integrated HI emission ∫ I(v)dv is shown in greyscale in Figure 1. These VLA observations combine C and D configurations and, with tapered uniform weighting, achieve 20″ resolution. The peak column densities of 3.7 × 1021 cm-2 can be seen to lie in two arms around the nucleus, coincident with enhanced 20 cm continuum emission (Fig. 1, left). This continuum emission traces the spiral arms of Maffei 2 as seen in the near infrared (Hurt, et al. 1993, A. J., 105, 121). Very little HI is present in the nucleus, although the region between the dashed lines is strongly affected by extinction/emission from foreground Galactic HI clouds. There is a strong N/S asymmetry in the HI distribution that reflects the observed peculiar morphology in the radio continuum near infrared.