The ISO SWS spectrometer has enabled us to detect for the first time the emission lines from the pure rotational transitions of molecular hydrogens (H2). We have been investigating the physical conditions and the excitation mechanisms of H2 in bright IR galaxies. Here, we present the preliminary results for NGC 6240, which is probably the most interesting object in our sample because of its largest known H2 luminosity.

Non-axisymmetric gravitational potentials are likely to play an important role in generating central activity in galaxies, i.e. starbursts and/or active galactic nuclei (AGN). For instance, the often observed secondary bars embedded in larger, primary, ones (Friedli & Martinet 1993; Wozniak et al. 1995; Friedli et al. 1996) might play a key role in feeding AGN, by accreting gas down to the centre at scales of a few parsecs. On the other hand, the frequent presence of a nuclear ring of star formation located between both bars indicates that double-barred galaxies are intimately linked to the formation of some circumnuclear starbursts. This type of galaxies might give useful clues to the connection between starbursts and AGN.

Below, as part of a larger sample of nearby barred galaxies (Wozniak et al. 1997a) being taken by ISOCAM on board of the ISO satellite, we briefly discuss the characteristics of the circumnuclear mid-infrared (MIR) emission of two double-barred galaxies, namely NGC 4321 (M100) and NGC 1097. The observations were done using LW2 (5–8.5μm) and LW3 (12–18μm) broad band filters at the 1.5″ px−1 PFOV.

Data which are obtained today can be re-acquired better and faster in the future. Their only enduring value, after they have been interpreted, is as historical markers. With electronic archiving one can envision archives covering decades, centuries and even longer periods of observations of selected objects or classes of objects. Such a data base would allow the study of phenomena with low temporal frequencies, and of rare events.

First hints of such phenomena in AGN have been discovered recently: 1) The Seyfert 1s, the best studied AGN at present, exhibit flux variations on time scales ranging from hours to several years (see Ulrich et al. 1997). The faster variations (up to months) have been extensively observed, and they are best understood as being caused by magnetic flares in the corona above the central part of the accretion disk (Blandford and Payne 1982). The origin of the long term and large amplitude UV/optical flux variations (factor 20 in several years as observed in NGC4151 and F9), however, remain essentially unknown.

We present speckle masking observations of Seyfert galaxies with the Russian 6 m telescope. Diffraction-limited resolution of 76 mas in the K-band was obtained for the first time. This resolution is similar to the resolution of recent MERLIN and VLA observations of galactic centers, thus allowing us to study the radio-IR spectrum of the same structures. Figure 1 shows the decreasing K-band visibility function of NGC 1068 and the contour plot of our reconstructed image. The results show that NGC 1068 is resolved with a FWHM diameter of 30 mas or 2 pc for an assumed Gaussian flux distribution. The image is elongated in northern direction, which is approximately the direction of the radio jet. In the right panel of figure 1 the observed flux values at 5,15 and 22 GHz (from) are plotted together with our K-band flux. The spectral index between 5 GHz and the K-band is approximately 1/3. This spectrum can be explained by synchrotron emission of quasi-monoenergetic relativistic electrons (as for our Galactic Center by). Assuming that the observed flux is mainly nuclear light (from, for example, scattering lobes above and below a torus, without absorption and re-emission) we use the same synchrotron model as has been used for the Galactic Center to explain our data. With this model, we find a source radius of R ∼ 1015 cm, a magnetic field of B ∼ 11 G, a electron number density of ne ∼ 1.1103 cm−3 and a mean electron energy of ∼ 2.7 GeV. The corresponding model spectrum is shown in the right panel of fig. 1. The observed flux value at 2.2 μm lies slightly above the model spectrum. This could be caused by flux contributions from additional components, for example, a central stellar cluster, an accretion disk or thermal radiation from a dusty torus. We have also observed the central regions of other galaxies. For example, for NGC 4151, we found a dominant central core, which is not resolved, and therefore has a diameter of < 20 mas.

It is well known that about 10% of galaxies harbour an Active Galactic Nuclei (AGN). A debated question is whether the activity influences the stellar population, or inversely, whether the level of activity is induced by the stellar population. By inspection of AGN spectra of low activity level, it is obvious that starlight contributes to a substantial fraction of the light.

NGC 1275 is one of the enigmatic blazars. The nature of central sources of blazars is open to discussion. Variability measurement of continuum is a major touchstone in the understanding of the nature of central sources of AGNs. Below we examine the intranight optical variability of NGC 1275 nucleus using our observations in 1982-1994.

Although the galaxies in our sample are heterogenous in their optical classifications (LLAGN: M51, NGC 3147, NGC 4258; LINER: NGC 3079, NGC 3310, NGC 3998, NGC 4579, NGC 4594; starburst: M82, NGC 253, NGC 3628, NGC 6946), they are fit well by a “canonical” spectrum with a hot, optically-thin thermal component with T ~ 8 × 106 K and an absorbed (NH ~ 1022 cm−2) power-law with an energy index α ~ 0.7–0.8. Both the “soft” component, most likely due to SN or superwind-heated ISM, and the “hard” power-law, most likely due to a micro-AGN and/or blackhole candidates, appear to be common in low-activity galaxies. If the soft component is associated with a superwind outflow, than ~ 10% of the X-ray emission is due to “swept-up” ISM rather than superwind emission. The abundance of Fe relative to α-process elements tends to be sub-solar, possibly due to dust-depletion and/or type-II SN enrichment. The lack of short-term variability in the hard component suggests that if it is due to an AGN, then the mode of accretion is probably fundamentally different from “normal” Seyfert galaxies.

As an example of the power of near-infrared (NIR) Adaptive Optics imaging in the detailed study of central regions of galaxies, we present high-resolution K-band imaging of Mrk 273, in combination with interferometric radio continuum data.

We present preliminary results of our ongoing programme to obtain subarcsec resolution near-infrared (NIR) images and colour maps of the central regions of a sample of barred galaxies with circumnuclear starbursts, using the CFHT. In those cases where structure is seen in the broad band images, the NIR colour index maps confirm the location of dust lanes and regions of star formation. In those galaxies where the NIR broad band images appear featureless, the colour maps do show evidence for tightly wound spiral or ring structure, as hinted at in the optical.

Aoki et al. (1996) found outflowing gas in the Seyfert galaxy NGC 7319. The velocity of the outflow comes up to 500 km s−1 and its extent is 4 kpc. This outflow is one of the largest outflowing phenomenon that have ever been found in Seyfert galaxies. The radio emission found by van der Hulst & Rots (1981) aligns the outflowing gas. It suggests the radio emission has relation to the outflow. We have made higher resolution radio imaging of NGC 7319 with VLA to study in detail relation of radio emission to outflowing gas. These radio images have been compared to Hubble Space Telescope (HST) archival broad-band WFPC2 image. The systemic velocity 6740 km s−1 (Aoki et al. 1996) gives a distance of 90 Mpc for NGC 7319 assuming a Hubble constant H0=75 km s−1 Mpc−1. Thus 1″ corresponds to 450 pc.

Little is known about the long-term infrared variations of Seyfert galaxies. Are they large or small, fast or slow, regular or irregular? Do they possess variable components hidden at visible wavelengths? Can their variational time-scales give us information about activity on sub-milliarcsecond spatial scales? Do the infrared measurements show well-defined flux variation gradients? Is the infrared flux delayed with respect to changes in the output of the central engine? And do the infrared variability studies support the “Unified Model”?

A narrow-band imaging observation of the Seyfert galaxy NGC1068 was made in the Fabry-Perot mode of the Kyoto 3D Spectrograph attached to the 188cm telescope of the Okayama Astrophysical Observatory. We observed at wavelengths of Hα, [S ii]λ6716, [S ii]λ6731 and adjacent continua of the respective lines with a “tunable filter”, i.e. a gap-scanning etalon with a spectral resolution of 20 Å.

In this short paper, we report the main results of a comprehensive theory of bar-driven spiral density waves. The theory offers explanations of the morphological difference of the spirals observed in the gas-dominated central disks as well as the different patterns of isovelocity curves distorted by the waves. It also gives reliable estimates of the induced mass flux to fuel the AGNs and starburst ring activities and hence the lifespan of the central disks. In particular, we compare our results with the CO and HCN observations of NGC1068 and M100. Based on these results, we can speculate the possible origin of the central bars and will propose two critical observational tests of the theory.

We have analyzed a sample of 1150 type ab, and 550 type c RR Lyrae stars found in 24 of 94 bulge fields of the MACHO database. These fields cover a range in Galactocentric distances from 0.3 to 1.6 kpc. In combination with the data on the outer bulge fields of Alard (1997) and Wesselink (1987), here we present the surface density distribution of bulge RR Lyrae between 0.3 and 3 kpc.

The central unresolved source of the galaxy NGC 1275 in red has a dimension of about 8″, but in blue its bright part is about of 0.″5. HST observations, obtained with the filter λ 2200Å cannot reveal the structure of the source inside 0.″26. Now we have collected the observed features of NGC 1275 nucleus in optics and radio domains, which are possibly associated with the complex structure of the nucleus.

Large numbers of Wolf-Rayet stars in the nearby (4.1 Mpc) star-bursting dwarf galaxy NGC 5253 indicate the starburst is only ~ 5 million years old (Schaerer et al. 1997). This makes NGC 5253 an ideal object for studying the early phases of starburst activity, in particular superbubbles blown by supernovae and winds from massive stars.

Previous low resolution observations suggested the observed X-ray emission was due to a superbubble. We use the enhanced resolution available with a long ROSAT High Resolution Imager (HRI) observation and find that the X-ray emission arises from several unresolved sources associated with the young star clusters seen in the optical. We discuss the possible origins of the point-like emission, and find that they could be small superbubbles blown by the individual clusters of massive stars.

We have surveyed the Galactic center (GC) for OH/IR stars, evolved late-type stars of different masses - and thus ages - in a short-lived stage of heavy mass-loss. By observing the 1612 MHz OH masers generated in their circumstellar shells, it is found that a considerable fraction of these OH/IR stars has the same high-valued shell expansion velocity of 19 km s−1.

M82 (NGC 3034) is a nearby (D = 3.3 Mpc) “prototypical” starburst galaxy which emits most of its luminosity in the infrared (LIR = 3×1010L⊙, see Rieke et al. 1980). M82 is also a strong radio source 3C 231, with numerous compact knots which are thought to be young SNR's (Kronberg et al., 1981; Muxlow et al., 1994). Its strong 1.4 GHz radio continuum is extended over the entire 500 pc nuclear starburst region, and the HI absorption is easily mapped at 2″ (30 pc) resolution using the VLA. The resulting velocity integrated optical depth (τΔV) map can be converted to HI column density map if HI spin temperature (Tsp) is known.

The main results of this study can be summarized in the following:

1. (a) Magnitude-limited complete sample of barred galaxies was constructed. Space density of barred and unbarred galaxies at low luminosity range (M >-20) almost the same. At the high (M<-20) luminosity range about 30% of the galaxies are barred ones.

2. (b) Bars do not have obvious influence on active nuclei. Presence or absence of bars does not related with the large scale galaxy environment.

3. (c) Barred spirals, on average, have significantly higher relative star formation rate than that do unbarred galaxies.

4. (d) Barred spirals exhibit tight correlations between FIR, radio and X-ray luminosities, while for unbarred spirals these luminosities do not correlated, which indicates on enhanced star formation activity in barred galaxies.

5. (f) Group and non-group barred galaxies may differ by star formation activity.

We study star formation and chemical evolution in the LMC Bar centre with the HST PC and uvby photometry. For all bands, mean turn off star data have σ around 0.015 mag. Present data have zero points from stars in M67. b-y of these stars coincides with target turn off. All measurement bands have zero point accuracy better than 0.010 mag.