Photoionization and shock models of the extended emissionline regions (EELRs) in active galaxies demonstrate that the optical emission lines alone are a poor discriminant of the excitation mechanism. Combining optical and UV data provides a discriminant between nuclear photoionization and autoionizing shock models. Hubble Space Telescope UV spectrophotometry of two Seyferts suggests that the EELRs in these objects are probably photoionized by the nucleus.

We present measurements of the central ionizing photon flux q across three spatially resolved Seyfert NLRs, with implications for the ionization mechanisms.

The excitation mechanism of the extended emission-line regions (EELRs) in Seyfert galaxies is commonly thought to be nuclear photoionization. However, some Seyfert galaxies have EELRs with disturbed kinematics, outflows, and morphology which is indicative of interaction between radio plasma and the ISM of the host galaxy. In these cases shock excitation must also be considered (BickneU 1993).

To investigate the importance of shocks and photoionization, we have taken two approaches: mapping the spatial dependence of the line ratios, and using UV line ratios which are sensitive discriminants between shocks and photoionization.

Studies of OH and H2O masers contribute to our understanding of the dynamics and physical conditions in the innermost few parsecs of AGN. Angular and velocity resolutions that may be routinely achieved with radio interferometry are substantially better than those possible with traditional observational techniques in the optical and ultraviolet.

The presence of two quasars symmetrically displaced from the nucleus of the galaxy NGC 4258 (Pietsch et al. 1994) has given rise to some speculation that they might have some dynamical connection with the high-velocity maser emission seen in the nucleus (Burbidge 1996; Ozernoy 1996). The case that the masers define a simple Keplerian disk is very compelling; nonetheless, it is instructive to investigate whether any other dynamical models could fit the available data.

The evidence that the masers define a thin Keplerian disk can be found in Miyoshi et al. (1995) and Moran et al. (1995). Some of the relevant data are shown elsewhere in this volume (Fig. 2 of Greenhill’s paper). The basic analysis is as follows. The features near the systemic velocity of 470km s−1 show a linear dependence of line-of-sight velocity versus distance along the major axis, while the redshifted and blueshifted high-velocity features show a nearly Keplerian dependence with distance.

III Zw 35 is an OH megamaser galaxy which is of great interest. In this paper, the spectrum has been fitted and the position map has been studied. A new model of multiple and distinct rotating and expanding rings in a thin disk is proposed in this paper.

We present a numerical example of a warping mode in the maser disk of NGC 4258. We find that the characteristics of the mode agree with the observed position and velocity distribution of the maser sources.

The preliminary results of several on-going AGN programs using the 2.16-m telescope at Xinglong Station of Beijing Astronomical Observatory are described. About 150 new AGNs including QSOs, BL Lac objects, and Seyferts have been discovered in the last two years.

In order to discover emission-line galaxy (ELG) candidates towards the Hydra Void, an objective-prism survey was undertaken. As a first step, five fields were observed with the UK Schmidt Telescope, and we discovered a total of 33 candidates on a single prism plate through the [O III] λλ4959, 5007 emission feature.

A cross-correlation between the IRAS PSC and the ROSAT All-Sky Survey has provided 242 sources detected in both surveys (Boiler et al. 1992). About half of these have redshifts in the literature and a spectral classification. An unexpected result was the discovery of many galaxies with X-ray luminosities up to a few 1043 ergs s−1, yet without Seyfert characteristics in their optical spectra (e.g., Boiler et al. 1993). To investigate this problem further and evaluate the frequency of occurrence of these peculiar objects, a spectroscopic follow-up has been undertaken to:

1. • Determine velocities and luminosities for all the unclassified objects.

2. • Reevaluate the classification of high X-ray luminosity objects previously not recognized as Seyferts. In particular, spectral resolution or coverage and variability are important parameters to consider if one wants to detect faint signs of Seyfert activity.

Through combined ROSAT and VLA observations, we have identified 19 BL Lac/quasar candidates. In 1994 December, 1995 January and October, and 1996 January 1996, we obtained spectra of all 19 candidates using the 2.16-m telescope of Beijing Astronomical Observatory. The dispersion used is 195 Å mm−1, which yields a dispersion of about 4.65 Å pixel−1, and the wavelength coverage is 3500–7800 Å. Five of these objects are uniformly featureless, and we identify them as BL Lac objects. Three new quasars are also identified. Table 1 presents VLA positions and redshifts for the 5 new BL Lac objects and three new quasars. By checking them in the NASA/IPAC Extragalactic Database (NED) and Véron-Cetty & Véron’s (1993) Catalogue of Quasars and AGNs, and other recent reports about discovery of new BL Lac objects and quasars, we find that these sources are previously unreported.

A program to identify bright ROSAT sources is being carried out with the 216-cm and 60-cm telescopes at Xinglong station. As the result of the first run, five bright low-redshift quasars have been discovered.

We used the CCD camera and spectrograph of the 2.16-m telescope of Beijing Astronomical Observatory to identify the ROSAT All-Sky survey sources in two 2° Ü 2° fields. Of a total of 16 X-ray sources, we identified 13 of them as follows: two QSOs, two Seyfert galaxies, two active galaxies, two clusters of galaxies, and five late-type stars. Three X-ray sources remained unidentified.

We describe a new sample of Seyfert nuclei discovered during the course of an optical spectroscopic survey of nearby galaxies. The majority of the objects, many recognized as AGNs for the first time, have luminosities much lower than those of classical Seyferts and populate the faint end of the AGN luminosity function. A significant fraction of the nuclei emit broad Hα emission qualitatively similar to the broad lines seen in classical Seyfert 1 nuclei and QSOs.

Redshift surveys of the extragalactic IRAS sources have revealed a class of galaxies, ultraluminous infrared galaxies (ULIRGs), that radiate an enormous amount of energy in the far-infrared (Soifer et al. 1986), typically LIR ≥ 1012L⊙, which is comparable to the luminosities of quasars. The energy source for most ULIRGs is believed to be massive nuclear starbursts triggered by galaxy interactions or mergers (Rigopoulou et al. 1996, Crawford et al. 1996). There is much debate about the evolution of ULIRGs. Sanders et al. (1988) suggested that ULIRGs are forming QSOs. However, it is not clear how merging galaxies evolve to QSOs. Meanwhile, observations and N-body simulations show that mergers between disk galaxies can form ellipticals. Some ULIRGs, such as Arp 220 and NGC 6240, do have elliptical characteristics. What is the evolutionary connection between QSOs and elliptical galaxies? About 10% of ULIRGs are IR QSOs or Seyfert 1 galaxies, on the basis of their optical spectra and appearance. Some of them are hosted in ellipticals (Hutchings et al. 1988, Lipari et al. 1994). Also, most of them are strong Fen emitters. Studying this subsample of ULIRGs in detail may give some clues to understanding the evolutionary process mentioned above.

We have constructed composite spectra of a large sample of flat-spectrum radio sources. The spectra are all very similar over a wide range of radio and optical properties, and are also similar to a composite of optically selected QSOs. We find, however, that the forbidden lines of the very reddest objects are anomalously strong.

Luminous infrared galaxies (LIRGs), denned by the criterion LIR ≳ 2 × 1011L⊙ (for H0=75 kms−1 Mpc−1), are the most powerful IR sources in the Universe, with most of their emission (~ 90%) in the far-IR. Most LIRGs are interacting/merging galaxies with large amounts of molecular gas as revealed by CO surveys (Sanders et al. 1991; Solomon et al. 1996). However, whether starbursts or dust-enshrouded AGNs/QSOs dominate the IR luminosity is not resolved.

CO may not trace the active star-forming regions where gas density is more than one order of magnitude higher than the average. Dense molecular gas is better traced by high dipole-moment molecules like HCN and CS (e.g., Nguyen-Q-Rieu et al. 1992; Gao & Solomon 1996). Therefore, it is essential to survey HCN emission in a large sample of LIRGs to better reveal the nature of LIRGs. We here study IR and molecular gas properties vs. galaxy-galaxy interactions in LIRGs over various merging phases to trace their evolution and explore some links among interactions, starbursts, and AGN phenomena.

An equivalent-width limit EW < 5 Å has been imposed as a selection criterion for BL Lac objects. However, such sharp cutoff has no physical meaning, and it is likely to be biasing BL Lac samples. This result is suggested by the analysis of a sample of low-luminosity, flat radiospectrum sources selected for the purpose of investigating the limits of BL Lac phenomena. In this work it is proposed that, instead of imposing sharp limits on the quantities observed, we should look for clear breaks occurring in the distributions of the observed properties for each sample.

We discuss new optical spectra and DSS images of a complete sample of very luminous IRAS galaxies. The statistics of classification of spectral types and interactions show that interaction can account for the nuclear activity (AGN and starburst) of ultraluminous infrared galaxies.

Unification theories have been central to much of our recent progress in the study of active galactic nuclei (AGN). These theories often explain the differences between some observationally defined classes of objects as due to what might be considered ‘uninteresting’ or nonfundamental parameters, such as viewing angle. In this presentation, I discuss not only such orientation-dependent unification theories, but also expand the concept to unification through other means, such as evolutionary effects.