Rotation curves of spiral galaxies have been thought to rise rigidly in the central a few kpc, while they are flat in the outer regions (Rubin et al 1982; Persic 1996). On the other hand, CO-line and recent Hα observations have revealed steeply rising rotation curves near the nucleus (Sofue 1996,1997; Sofue et al 1997a,b; Rubin et al 1997).

Sofue (1996, 1997) presented accurate rotation curves of nearby galaxies, which are almost completely sampled from the inner to outer regions. The conspicuous common feature of the rotation curves is a steep rise at the inner bulge. The rise suggests a compact massive concentration near the nucleus (Sofue 1996). The study of the light distribution at the inner bulge demands accurate surface photometry at near-infrared wavelengths, where dust extinction is much less effective than in the optical. Most of Sofue's samples are nearby large galaxies, so that observations with a wide field view is clue to constructing reliable light distribution models.

One of the main aims with respect to the evolution of spiral galaxies is to clarify how the disk and bulge were formed. The study of bulges has usually been focused on how bulges resemble to elliptical galaxies. For the study of the evolution of elliptical galaxies, the color-magnitude relation (C-M relation) gives us a clue to understanding the formation and evolution of ellipticals. In fact, the tight C-M relation of ellipticals (Bower et al. 1992) was interpreted as the sequence of the metallicity difference (Kodama and Arimoto 1997). On the contrary, there are few observations for the C-M relation of bulges. On the analogy of elliptical galaxies, the C-M relation of bulges, if it exists, may be one of the most important clues to understanding the formation process of bulges. The main goal of the present study is to investigate the C-M relation of bulges.

There are two star clusters near the Galactic Center which might be similar to the central parsec cluster. One is the Quintuplet cluster at (l = 0.16°, b = −0.06°), and the other is the Object #17 cluster at (l = 0.12°, b = 0.02°). The Quintuplet, first found in a polarimetric survey by Kobayashi et al. (1983), includes five very bright stars whose color temperatures are in the range of 600-900K (Okuda et al. 1990; Nagata et al. 1990). Object #17 is a cluster of emission line stars (Nagata et al. 1993, 1995; Cotera et al. 1996; Morris & Serabyn 1996). Spectral features of these two objects observed with the ISOCAM (Kessler et al. 1996; Cesarsky et al. 1996) have been reported (Nagata et al., 1996); absorption features due to O-H (2.8μm) CO2(4.3μm), and CO (4.7μm) are present. In this paper, we report diffuse emission components detected in these two fields.

The Quintuplet cluster contains over two dozen post main sequence descendants of massive O-stars, including Wolf-Rayet and OBI stars.

The five Quintuplet-proper members (QPMs) may be dusty late-type Wolf-Rayet carbon stars (DWCLs), and the Pistol star may have a very high luminosity, ≈ 106.7±0.5 L⊙. Coupled with its rather cool temperature, 12–23 kK, the Pistol Star is well in violation of the Humphreys–Davidson limit. We argue that the surrounding “Pistol” nebula was ejected from the star a few thousand years ago.

The cluster stars imply the following approximate cluster properties: tage ∼ 2 to 7 Myrs, M ∼ 104 M⊙, L ∼ 107.3±0.2 L⊙, and NLy,c > 1049.9 s−1. The “Sickle” (G0.18–0.04) radio feature and the mid-IR ring (seen in MSX images) may naturally be explained by the presence of a young cluster and a nearby molecular cloud.

The details of current and past star formation episodes and the stellar content of the central parsecs of our galaxy are still not very well known (Mezger et al., 1996). We have therefore begun an observing program to study star formation processes in the nuclear bulge. Here we discuss the technical aspects of this program, while the scientific goals are presented by Zylka et al. (1997).

Massive but invisible black holes (BH) are often assumed to lurk in the center of many galaxies but definitive proof of their existence has not yet been established. However, in the surrounding stellar cluster stars are unavoidably being destroyed by tidal disruptions and stellar collisions liberating of order 1M⊙ in each event. The subsequent accretion of this gas by the BH could bring it back to “life” and reveal its presence.

Star formation in the Galactic Center (GC) happens under unusual conditions, which include high gas temperatures, high velocity dispersions, and strong tidal shear (Spergel & Blitz 1992; Blitz et al. 1993). All these conditions may lead to an initial mass function (IMF) dominated by massive stars (Morris & Serabyn 1996). A history of chemical evolution dominated by massive stars is expected to result in enhancements of α-elements (Mg, Si, Ca, Ti) relative to Fe (Wheeler et al. 1989). This argument is the main motivation to study the abundance of Fe and Mg in GC stars.

The analysis of resolved DENIS (Deep Near Infra Red Survey of the Southern Sky) I,J and K band data shows good evidence (≳ 3σ) in the J and K band number counts to support the existence of a kiloparsec-scale bar with its major axis in the first quadrant. A star by star dereddening of this K data combined with supplementary nbL band data (3.6μm) gives number count contrasts consistent with low angle (≲ 20 degrees) bar models in the literature.

In 1993 I have started an observational program to search for decoupled galactic nuclei with the Multi-Pupil Field Spectrograph (MPFS) of the 6m telescope (Afanasiev et al. 1990); a list of 34 northern candidate galaxies with photometrically distinct red nuclei (Sil'chenko 1994) is used.

Because it is inevitable to lose some information in the process of one dimensional luminosity profile extraction, we developed a two dimensional luminosity decomposition method in order to examine the structure of galaxy such as bulge, bar and spiral arms.

Generally, it is believed that there is a supermassive black hole and a surrounding accretion disk in a central region of active galactic nuclei (AGN). However, it is quite difficult to obtain direct information about the center of AGN, because the accretion disk size is far too small to resolve.

Dynamical collapse of rotating cloud and subsequent mass supply to the central object is the basic physical process on the formation of the central black holes in the high-z QSO cosmologically. Considering the formation of super massive black holes, the centrifugal barrier plays an important role. In this contribution, I consider the viscous effect to the self-gravitating disk which formed cosmologically. In particular, unsteady growth of the central core is treated consistently with surrounding accreting disks semi-analytically. A new self-similar solution of axisymmetric viscous accretion onto an evolving point mass is obtained. Application to QSO progenitor black hole formation is briefly discussed.

We investigated the oscillation of a dense stellar system which harbours a massive object, presumably a supermassive black hole, in its center. The central mass moves in response to the oscillation of the stellar system. This phenomenon may explain the asymmetric structure observed in M31 (Lauer et al., 1993), or NGC4486B (Lauer et al., 1996). Moreover, the motion of the central massive black hole may well induce the accretion of gas onto the black hole itself and ignite the activity in galactic nuclei. We first investigated the stability of a fluid disk around a massive object by linear modal analysis. Next, we performed N-body simulations for spherically symmetric, rotating, particle systems with a central mass.

We study numerically the dynamical evolution of models of stellar systems which contain two heavy centers of gravity and extended shells inside and around orbits of these binaries. Initially the binary components surrounded by numerous small-mass particles on shells with small initial velocities. It is shown that at some moment of time there is a collapse of these particles on to the heavier component of the binary. We have the strong interactions of bodies at this time. Frequently, the ‘gravitational slingshot’ effect occurs. Further in time, some part of particles which initially were outside the binary orbit escape from the system. Other particles are captured by binary components forming in the center a ‘dumb-bell’ bar. During evolution of our models different kinds of structures of systems often are very similar to the observed structures of galaxies: spiral and elliptical galaxies, interacting galaxies, different kinds of flows and jets. Totally systems are expanding. Formation of different kinds of structures of galaxies depends on motions of particles with respect to the line of apses of the nuclear binary: 1. in the case of almost orthogonal motion (the gravitational slingshot effect), these particles escape from systems and before an escape form open expanding spirals; 2. in the alternative case (small angles of motion of the particles with respect to this line), these particles are captured by the binary components; 3. in the intermediate cases, particles form different kinds of flows like jets, rings, close spirals etc.

The spectrum of the dwarf Seyfert 1 nucleus in NGC 4395 was first reported about a decade ago (Filippenko & Sargent 1989), showing high ionization narrow emission lines and broad permitted lines. The later detection of radio and X-ray compact nuclear sources and of a featureless UV continuum gave support to the idea that NGC 4395 is a genuine low luminosity AGN (Sramek 1992; Filippenko, Ho & Sargent 1993). However, it has been claimed that, unlike classic Seyferts, NGC 4395 does not vary at all (Shields & Filippenko 1992).

We present the velocity fields for the ionized gas and the stars obtained from 2D fibre spectroscopy in the central regions of a sample of active (NGC 985, NGC 1052, NGC 6500) and non-active (M31, M32) galaxies.

Star formation presently occurs in our Galactic nucleus at a rate of several 10−1 M⊙ yr−1. If this value represents the long-term average, some 109 M⊙ of stars should have been generated in our Galaxy's central few hundred parsec volume over the Milky Way's lifetime. As the expected stellar yield is actually in rough agreement with the mass of our Galaxy's bright near-infrared “central r−2 cluster”, it is possible to hypothesize that this massive “nuclear” cluster is in fact the product of long-term nuclear star-formation, rather than being a remnant of the Galaxy's formation epoch. Several lines of evidence supporting this hypothesis are laid out in Serabyn and Morris (1996), to which the reader is referred for a complete discussion and reference list; here only a brief summary of the main arguments is presented.

Since its launch in November 1995, the Infrared Space Observatory ISO has converted mid-infrared spectroscopy into a mature tool. Due to its proximity, brightness, and the wealth of complementary information, the center of our Galaxy remains a unique testbed for studies of galactic nuclei. A first analysis of the 2.4-45μm spectrum obtained with ISO-SWS (Fig. 1) has been presented by Lutz et al. (1996a). One of the surprises is a determination of the mid-infrared extinction law from comparison of the Galactic center hydrogen recombination line fluxes and case B expectations: The extinction law clearly lacks the deep minimum near 7μm expected for standard graphite/silicate mixes. External galaxies are less close to the ideal ‘screen’ case and cannot provide the detail of the GC recombination line spectrum needed to derive an extinction law. However, simple ratios of the strongest recombination lines are inconsistent with a classical extinction law and any dust configuration.

I discuss the role of galactic bars in the fuelling of (circum)nuclear activity. Since the majority of all galaxies are barred, the presence of a bar in a Seyfert galaxy cannot be the sole reason for their activity, although it appears to be a necessary condition for activity. Two options for further work are being explored, high-resolution near-infrared imaging of samples of active and non-active galaxies, and detailed case studies of selected galaxy cores.