The early study of radio sources at visible wavelengths and the first empirical evidence that galaxies can have strong dynamical interactions are closely intertwined. Baade & Minkowski's (1954) model of Cygnus A as a pair of galaxies in collision, while now believed to be incorrect, presaged the merger-driven picture for the generation of radio sources (e.g. Heckman et al. 1986) by some 30 years. Morphological evidence for an association between mergers and radio loud AGN is seen in both the nearest radio galaxies (e.g. Cen A; Schweizer 1986) and in the most powerful sources at z ~ 0.1 - 0.3 (Stockton & Mackenty 1983; Hutchings et al. 1988; Heckman et al. 1986).

The first statistical study of the environment of Seyfert galaxies (of both types 1 and 2) was done by Petrosian (1982), who found that Sy2 galaxies had an excess of nearby companion galaxies with respect to field galaxies. Dahari (1985) made a similar study, and obtained that both types of Seyfert galaxies are found five times more often in interacting systems that “normal” galaxies. Fuentes-Williams & Stocke (1988) obtained the opposite result: that Seyfert galaxies have no significative excess of nearby companions, and MacKenty (1989) obtained the same result as Petrosian. The last papers appeared in 1995: Rafanelli, Violato & B.aruffolo (1995) obtained a similar result as Dahari. Laurikainen & Salo (1995) made a careful attempt to understand the discrepancies; they concluded that the incompatibilities in the results were mainly due to control sample selection, and problems in background galaxy determination. Their work confirmed the result of the first study. However, in order to explain the discrepancies between previous results, they also used incorrectly defined control samples. Objections can be made against all of these works for this only reason. We have repeated the study using, for the first time, the digitized Palomar Sky Survey plates (paSS), an automated selection procedure, and correctly defined control samples (Osterbrock 1993).

The distribution of black hole (BH) masses M• in galaxies is constrained by photometric and kinematic studies of individual galaxies, and by the properties of the quasar population. I review our understanding of these topics, present new results of adiabatic BH growth models for HST photometry of elliptical galaxies with brightness profiles of the ‘core’ type, and discuss the implications of ground-based stellar kinematical data. It is not yet possible to uniquely determine the BH mass distribution, but the available evidence is not inconsistent with a picture in which: (i) a majority of galaxies has BHs; (ii) there is a correlation (with large scatter) between M• and spheroid luminosity Lsph of the form M• ≈ 10−2Lsph (solar B-band units); and (iii) the BHs formed in a quasar phase through mass accretion with efficiency ε ≈ 0.05.

One of the most important results of the IRAS survey is the discovery of a class of “Luminous Infrared Galaxies” (LIGs), which emit most of the energy in the infrared and are the dominant population in the local universe at luminosities above 1011L⊙ (e.g., Sanders & Mirabel 1996). All LIGs appear to be extremely rich in molecular gas, and many of them show evidence of recent interacting/merging activities. Hence it is now accepted that strong interactions of gas-rich galaxies triggers large central concentration of molecular gas, and makes optimal conditions for both enormous nuclear starbursts and building and/or fueling AGN. Actually, various observations show evidence of starburst activity as well as that of AGN in many LIGs (Sanders & Mirabel 1996).

The CFHT adaptive optics camera uses a visible light guide signal from a star to operate a bimorph mirror. The system is a unit that is operated by the observer and can be used with CCD or HgCdTe detectors. Pixel sizes are of order 0.04″. The amount of correction varies as the guide star brightness, the angular distance from it, and the natural seeing at the time. With good CFHT conditions, a guide star of 13 mag will give JHK images of FWHM near to the diffraction limit (0.1 to 0.15″) up to 20″ away. Correction is worse in the optical, but images of 0.2″ or better can be obtained in R and I-band. The camera performance is described by Rigaut et al (1998).

NGC 4314 (Benedict et al. 1996) has a complex nuclear morphology with recent star formation confined to a nuclear ring. HST observations resolve the nuclear ring into multiple sites of new star formation and resolve the associated dust lanes into discrete clouds. We construct dynamical models of this galaxy in order to provide plausible identification of the dynamical processes that led to the formation of the observed structure. We assume that the center of this galaxy contains a very massive double black-hole, surrounded by relatively low-mass particles - the star clusters as well as gas and dust complexes. Our previous work (Anosova & Anandarao 1994, Anosova & Tanikawa 1995) showed that the dynamical evolution of such a model produces many structures similar to those observed in galaxies of diverse types: spiral and elliptical galaxies, interacting galaxies, and various types of flows and jets. In the present work, we consider a number of such models with different initial parameters. We study their dynamical evolution of the gravitational N-body problem, taking into account strong interactions of bodies. Comparison of the evolution of our models with the observed structure, distributions and motions of stars, gas, and dust complexes in NGC 4314 shows good agreement. The model predicts the velocity fields observed in this galaxy.

Galaxy formation is a diverse range of ongoing processes. Numerical simulations suggest that disk galaxies in collision pass through a massive burst of star formation, and produce ‘elliptical–like’ remnants similar to bone fide elliptical galaxies. The observed relative numbers of merging systems and elliptical galaxies are consistent with this picture (Toomre 1977). We here investigate further by studying the distribution of old stars in a sample of merging galaxies : the ultraluminous IR galaxies (ULIRGs). We selected ten ULIRGs from the literature (Clements & Baker 1996; Leech et al. 1994; Zhenglong et al. 1991; Melnick & Mirabel 1990) by two criteria: proximity (redshifts z < 0.15), for good spatial resolution; and confirmed signs of merging. We obtained deep K–band images (tint ~ 1000 - 2700s) in good seeing using MAGIC on the Calar Alto 3.5m telescope. Our data have a field–of–view roughly equivalent to 10 - 20 effective radii for the galaxies. We have fitted analytic surface brightness profiles to the data for the exponential disk and the de Vaucouleurs r1/4 elliptical descriptions. We strongly favour the elliptical-like description in 8 out of 10 cases, supporting the picture that collision and merger of classical spiral galaxies can produce classical elliptical galaxies, through tidal disruption, violent star formation accompanied by prodigious infrared emission, and gravitational relaxation. These data can also constrain the properties of the ULIRG (double) nuclei and hence the lifetime of the ULIRG phase (Baker & Clements 1998).

A connection is suspected between quasars and ultraluminous IR galaxies (ULIRGs). Almost all ULIRG activity is triggered by mergers (e.g. Clements et al. 1996, MNRAS, 279, 477). We thus investigate the relationship between quasars and ULIRGs by examining the relationship between FIR luminosity and host morphology in quasars. We use the z < 0.3 imaging survey of PG quasars by McLeod & Rieke (1994, ApJ, 420, 58; 431, 137), and ancillary data, to determine which quasars in the survey have disturbed hosts. This is combined with FIR data from Sanders et al. (1989, ApJ, 347, 29). We apply Survival Analysis techniques to see if the FIR luminosity of the disturbed and undisturbed host quasars differ. We find, with 99.99% confidence, that the disturbed host quasars have higher FIR luminosity. We observe a small, but complete, sample of six quasars selected to have LFIR > 1011.8L⊙, and a comparison sample of quasars with similar redshifts and B-band absolute magnitudes, but without detected FIR emission. At least 3 of the FIR luminous quasars are found in disturbed hosts while the non-FIR luminous quasars all lie in undisturbed hosts. The FIR luminosity in ULIRGs is triggered by interactions. If ULIRGs evolve into quasars we would expect FIR luminous quasars to be younger, and to share more characteristics with ULIRGs, especially disturbed host morphology. These studies are consistent with this model for quasar evolution.

We present the results of a continuing programme to investigate the properties of the Ultraluminous IRAS Galaxies (ULIRGs) in a large sample selected from the IRAS Faint Source Catalogue and identified with the APM galaxy catalogue (for details of the survey selection and initial results see Clements et al. 1996, MNRAS, 279, 459). Observations now include optical imaging for a complete subsample to BJ = 19.5 (Clements et al. 1996, MNRAS, 279, 477) and near-IR imaging for a complete subsample to BJ = 19 (Clements et al. in preparation). Moderate resolution optical spectroscopy, ISOPHOT photometry and ISOSWS spectroscopy have also been obtained for smaller subsamples of this survey. New redshift measurements have identified 11 new ULIRGs, extending the sample size to 102 ULIRGs. These observations have extended the maximum redshift to 0.44, and have also discovered a new broad-line ULIRG at z = 0.351. Initial analysis of our ISOPHOT data, while subject to substantial calibration uncertainties, shows a broad range of 160–120μm flux ratios which might indicate the presence of cold dust (T ~ 20 K) in some objects. Such dust would not have been detectable by IRAS. Our continuing multiwavelength studies of ULIRGs will be used to examine the nature of the power source in these objects, and their relationship to other extragalactic populations.

Direct observational evidence of interaction driven inflow of gas toward a Seyfert nucleus remains scant. UGC 3995 is one of the rare systems of galaxies that, at a first glance, offers direct evidence of this phenomenon: a bright filament appears to connect the bar of the spiral galaxy UGC 3995A (whose nucleus shows a Seyfert 2 spectrum) to the nucleus of a smaller spiral companion (UGC 3995B) whose radial velocity exceeds by only 30 km s−1 that of UGC 3995A. Narrow (redshifted Hα) and broad band (R, B) images of UGC 3995, along with long slit spectra in the Hα region were collected at the 2.1 m telescope of the Observatorio Astronómico Nacional at San Pedro Mártir (SPM), México, in January-February 1995. From the B-R color map we infer that UGC 3995B is partially obscuring UGC 3995A. It is likely that a conspiracy of chance alignments and obscuration is giving the bar of UGC 3995A a disrupted appearance suggestive of stripping. The fairly regular profile of the HI 21 cm line suggests that the neutral hydrogen disks of both UGC 3995A and B have not yet undergone strong perturbations. However, while on the eastern side of UGC 3995A we observe HII region gas approximately following the rotation of the HI gas, on the western side we may be observing shock-heated “minority” gas whose motion is not exclusively rotational. We conclude that most of the morphological peculiarities observed in UGC 3995 cannot be easily related to infall of gas toward the Seyfert nucleus. Nevertheless, the kinematics of ionized gas in the western part of the disk of UGC 3995A has been affected by the intruder, probably because UGC 3995B is already physically in contact with UGC 3995A.

We present K′-band imaging and millimeter (CO) spectroscopy of a 60 and 100 μm flux-limited sample of 35 low redshift, powerful radio galaxies (LzPRGs: P178MHz > 1023.5 W Hz−1 and 0.01 < z < 0.22). These observations are being obtained to test the hypothesis that the radio activity in LzPRGs is triggered by the merger of gas-rich galaxies, as well as to look for evolutionary correlations between the degree of irregularity in the K′-band morphologies, the amount of star-forming molecular gas, and the radio morphologies.

Rest-frame 0.48–1.1 μm emission line strengths and molecular gas mass (H2) upper limits for three luminous infrared sources – the hyperluminous infrared galaxies (HyLIGs: Lir ≥ 1013L⊙ where Lir ~ L(8 – 1000μm) IRAS F09105+4108 (z = 0.4417), IRAS F15307+3252 (z = 0.926), and the optically-selected QSO PG 1634+706 (z = 1.338) - are presented. Diagnostic emission-line ratios ([O III] λ5007/Hβ, [S II] λ6724/Hα, [N II] λ6583/Hα, and [S III] λλ9069+9532/Hα) indicate a Seyfert 2-like spectrum for both infrared galaxies, consistent with previously published work. Upper limits on the molecular gas mass for all three sources are M(H2) < 1 - 3 × 1010h−2M⊙ (q0 = 0.5, H0 = 100h km s−1 Mpc−1), less than the H2 mass of the most gas-rich infrared galaxies in the local Universe. All three sources have Lir/L′CO ~ 1300 – 2000, the most extreme values for extragalactic sources measured to date. Given the relatively warm far-infrared colors for all three objects, much of their infrared luminosity may emanate from a relatively small quantity of hot dust near an AGN.

The role played by environment on nuclear activity in galaxies is not clear and largely debated (see e.g. Barnes & Hernquist 1992, Kelm 1996). To overcome statistical uncertainties, environment properties of two large samples of Seyfert galaxies (Sy 1 and Sy 2 have been kept separated) have been computed and compared with equivalent size “normal galaxy” sample ones. Seyfert samples have been extracted from the Veron & Veron catalogue (Veron & Veron 1996), whilst “normal galaxies” have been randomly extracted from ZCAT (Huchra 1993). The samples are limited in cz ([1500–9500] km/sec) and contain 149 Sy 1, 173 Sy 2 and 160 “normal galaxies” (hundreds of random extractions from ZCAT). For each galaxy neighbors have been computed (from ZCAT) within two variables radii, R (isolation radius) and r (pair separation), which span [0.2 - 2] h100 Mpc. and [20–90]h100 kpc. respectively. Neighbors must lie also within 700 km/sec from the galaxy. In this way, for each value of R and r, environment of each galaxy has been “quantified”.

As a solid physical mechanism to link between starburst activity and AGNs, we have proposed a radiative avalanche, where the mass accretion is driven by radiation drag exerted by stellar radiation from circumnuclear (ring-like) starburst regions (Umemura et al. 1997a,b). We here examine a radiative avalanche for a case of spherically distributed sources (Fukue et al. 1997). The results of the present spherical case are qualitatively similar to those of the ring-like case. For example, the drift timescale tdrift is found to be tdrift = 1.86×109 yr (m+1)(b/100 pc)2 (L∗/1012L⊙)−1g(r)−1, where m is the power of rotational velocity (vϕ ∝ rm), L∗ the starburst luminosity, b the radius of the starburst region, and g(r) a function of the order unity. This timescale is sufficiently shorter than the viscous timescale of the relevant region. In contrast to ring-like starbursts, the advantage of spherical starbursts is the large solid angle subtended by the starburst region. Hence, the luminosity of the starburst region is fully available to avalanche on the surface of the disk. Furthermore, the radiation field of the starburst region has no angular momentum, which is in favor for the avalanche.

We show that the nearby peculiar interacting galaxy NGC 2782 (Arp 215) harbors a clumpy molecular CO bar. The gas bar has a radius of ~7.5″ (1.3 kpc), a mass of ~ 2.4 × 109M⊙, and leads a nuclear stellar bar of similar extent (Jogee et al. 1997b). We estimate the gravitational torque exerted by the nuclear stellar bar and find large gas inflow rates (≫ 1 M⊙ yr−1) into the central 200 pc where the starburst activity peaks. We suggest that the nuclear gas bar will disappear on timescales ranging from few × 108 years to a Gyr, under the effect of star formation, dynamical friction, and gravitational torque. We also show that NGC 2782 harbors a starburst-driven outflow with a remarkable bubble morphology that has not been observed to date in any other starburst galaxy of comparable luminosity (Jogee et al. 1997a). The outflow is driving hot, warm, and possibly cold phases of the ISM out of the central kpc. The estimated outflow rate is less than the inflow rate, and this suggests the dynamical mass in the inner 100 pc might increase by several folds within a Gyr. These results might be relevant to theory (Shlosman et al. 1989) and simulations (Friedli & Martinet 1993) which propose nuclear bars and ‘bars within bars’ as efficient mechanisms for fueling central starbursts/AGNs.

We are investigating a sample of nearby interacting and merging galaxies showing starburst properties and/or nonthermal nuclear activity (e.g. Mrk 231, Mrk 739, Mrk 1027, NGC 2992, Arp 92).

We report the detection of a FR I-like radio galaxy with a total extent of more than 200 kpc in a disk-dominated host. Traditional wisdom maintains that these types of radio sources are only found in elliptical hosts. We confirm the optical classification of this galaxy from deep, multicolor optical/NIR imaging and the detection of a spiral arm, an optical rotation curve, and line-ratios in the disk consistent with HII regions and star formation. At 20cm, we find a 36kpc knotty, jet extending into the southern lobe. At 3.6cm we detect a kpc-scale jet with the same position angle. With the exception of the radio source, this galaxy appears to be a fairly ordinary, dusty, star-forming spiral, with some evidence for a weak, obscured, AGN.

We observed two ULIRGs, IRAS 20551–4250 and IRAS 23128–5919 with the X-ray satellite ASCA. Both of them are merger, 100μm bright galaxies with LIR ~ 1012L⊙ and have a “warm” IRAS color (25μm/100μm ≥ 0.2), so the presence of an AGN would be expected.

We report the results of near-infrared observations of a type-2 QSO, AX J08494+4454 at z = 0.9 which was identified in our optical follow-up observations of the ASCA Lynx deep survey. This object has a hard X-ray spectrum with an X-ray luminosity of about 1×1044 erg s−1 in 2–10 keV. The optical spectrum shows high-excitation and high-ionization lines but no significant broad Hβ emission. These properties strongly suggest that this object is a “type-2” QSO (Ohta et al. 1996).

We have made a CO(J=2-1) observations using the Nobeyama 45m telescope aimed at examining the physical properties of the molecular gas in this object. The upper limit obtained is 1.8 mK (3σ) at a velocity resolution of 100 km s−1, which leads to an upper limit on the molecular gas mass of 5.3 × 1011M⊙, if we assume a line width of 250 km s−1 obtained in the CO(J = 5 - 4) line (rest-frame) and the Galactic CO-to-H2 conversion factor of 4.5 (M⊙ K km s−1 pc2). The line ratio between the 2–1 line and the 5–4 line as well as those from the 7–6 and the 4–3 lines (Omont et al. 1996, Nature, 382, 428) imply that the mean gas density is as high as 103–5 cm−3, which is comparable to that in nearby star burst galaxies (e.g., Solomon et al. 1992, ApJ, 387, L55).