The results from optical and radio studies of a flux limited sample of luminous infrared galaxies in the Southern Hemisphere are reported. The detailed study of the nearest (z ≤ 0.13) ultraluminous infrared galaxies (Lir ≥ 1012L1) show that these are mergers of giant gas-rich systems with critical separations of 10 kpc. Merging of gas-rich galaxies enhance molecular cloud formation, as well as the infrared luminosity per nucleon of interstellar gas.

Arp 299 (Mrk 171), is an interacting system at 42 Mpc, comprising the galaxies IC 694 and NGC 3690. Interferometric CO maps at 6″ resolution (Sargent et al. 1987) showed compact molecular condensations at the nucleus of IC694 and in the overlap region of the galaxy disks [positions A and C – C in the terminology of Gehrz, Sramek, and Weedman (1983)].

As part of a multi-wavelength study of IRAS galaxies with large far-infrared-to-blue luminosity ratios, we observed an infrared-complete distance-limited sample of southern extreme IRAS galaxies in the CO(J=1−0) line with the 15 m Swedish-European Submillimeter Telescope (SEST) at the European Southern Observatory in March 1990.

We have surveyed a sample of 40 ultraluminous (L60μm > 1012L using H0 = 50 km s−1 Mpc−1 and Ω0 = 1) and 7 high-luminosity (11.7 < log(L60μm) < 12.0) IRAS galaxies with the aim of obtaining a better estimate of the fraction of ultraluminous IRAS galaxies in interacting systems. This is the largest imaging survey of such high-luminosity galaxies. The galaxies were selected from the North Galactic Wedge (Lawrence et al. 1986) and QDOT (Rowan-Robinson et al. 1990 MN in press) area and flux limited IRAS galaxy samples with complete z information. Imaging observations were carried out at the Observatorio del Roque de los Muchachos (La Palma) using the CCD imaging system at the f/3 focus of the 2.5m Isaac Newton Telescope. The average total exposure time per galaxy was 2000s, reaching a limiting isophote of R=26.

We report on the first sub-arcsecond resolution mid-IR images of the nuclei of galaxies from the IRAS ultraluminous sample. This sample contains galaxies which emit most of their energy in the far-infrared (10-100μm) and have luminosities approaching that of quasars. Previous observations in the mid-IR using single element detectors suggest that the IR luminosity is derived from a region smaller than the instrumental aperture, typically 5″(1.6 kpc at 65 Mpc). Our observations are capable of imaging the morphology of the mid-IR emission region to a factor of eight smaller than previously known.

1.3mm continuum observations for a complete sample of optically selected southern quasars show that most objects have flux densities below ≈40mJy at that wavelength. This clearly indicates that previously claimed detections at Jy level are erroneous. The sample is divided into radio-quiet and radio-loud objects. While for the first group a thermal origin of the FIR emission is very likely the latter group shows energy distributions dominated by Synchrotron radiation.

Megamaser emission of galaxies in the OH main lines 1665 and 1667 MHz /see, e.g., Baan, 1989/ is analysed. A semi-analytical time-dependent solution is obtained of a system of differential equations which includes the radiative transfer equation and the equation for population difference of the maser levels. The system was solved by the Euler's method. Various cases of solution perturbations, caused by time variability of the central radio continuum source are considered.

The physics of megamasers OH and H2O is considered shortly. Both phenomena concern clouds. OH megamasers are clouds of nearnuclear disk, H2O megamasers are clouds flying from or to AGN.

In a study based on the analysis of an IR colour-colour diagram (see Figure 1) of galactic nuclei associated with OH megamasers and water megamasers we conclude that:

1) OH megamaser galaxies are usually associated with galactic nuclei which are undergoing a burst of star formation. The colour temperatures of infrared emission are 50-80 K. The far-infrared spectra of OH megamaser galaxies are characterised by high excess in the 60 pm band over the 25 μm and 100 μm bands.

2) The known water megamaser galaxies are associated with two kinds of galactic nuclei which are characterised by starburst and disc components and starburst and Seyfert components respectively. The luminosities of far-infrared emission are much less than for OH megamasers. The colour temperatures of T(100/60) are almost double the colour temperatures of T(60/25). The infrared spectra have less excess in the 60 μm band than do OH megamasers.

3) We understand the mechanism of OH megamaser amplification in broad outline but not in detail. To make progress a programme of detailed calculations of OH populations must be initiated. In this manner we may be able to establish the nature of the environment in the maser zone and important properties of the parent galaxies. In particular we need to be able to reproduce observed line ratios in the 1667 and 1665 MHz main lines and to be able to show why 1667 MHz is strongly dominant. The nature of water megamasers remains obscure although observations do suggest that, as for OH megamasers, they operate through amplification of the background continuum emission.

About 40 OH megamasers have been discovered up to now, occuring in luminous IR galaxies; their far-infrared (FIR) luminosities, however, span a rather large range, from a few 1010 to several times 1012 solar luminosities.

In a comparative study, optical and radio spectra are presented in order to further investigate violent turbulent motions in starburst galaxies. Emission-line, HI and OH profiles of IRAS 10039-3338 exhibit signs of a highly perturbed far-infrared galaxy. Remarkably narrow and distinct OH components are shown in the megamaser spectra. A molecular mass of 1010 MO is deduced from CO observations. The presence of comparable numbers of blue and red-shifted components is apparently not in favor of an outflow interpretation.

During last two years (1988-1990) nineteen galaxies with megamaser emission have been observed in optical and radio wavelengths. Prime photographies of megamaser galaxies were obtained on 2.6m telescope of Byurakan Observatory. Spectral observations were carried out on 6m telescope of Special Astrophysical Observatory. Radio continuum observations at 3950 MHz have been done on the RATAN-600 radio telescope. Spectrogrammes of the galaxies were obtained with 1000 cannal one dimension scanner and in a few cases with two dimension scanner.

The 18-cm and 21-cm surveys of luminous infrared galaxies achieved with the Nanlay radiotelescope led to the detection of OH and/or HI absorption lines in 7 bright IRAS galaxies. We show that a careful comparison of optical radial velocities and 1) HI absorption line radial velocities or 2) HI emission line radial velocities gives valuable indication on the radial motions of the circumnuclear gas in our sample of galaxies and in the IRAS galaxies studied by Mirabel and Sander (1988).

We present the results from an HI survey of 160 IRAS galaxies with luminosities larger than 1010 L⊙. The observations were made with the Nanlay Radiotelescope and the overall detection rate is about 75%.

12CO (J=1−0) emission has been detected in the extremely extinguished galaxy NGC4418 with a 15″ beam on the 45-m telescope at the Nobeyama Radio Observatory. The inferred molecular mass is 4 108 MO at a distance of 25 Mpc. The CO line profile is single peaked with the FWHM of 85 km/s, suggesting that molecular clouds highly concentrate towards the center. For the column density estimated from these observations to be consistent with the extinction value 55 < Av < 120 derived from the 10μm silicate absorption by Roche et al (1986), most of the clouds should be confined within a central region of 3.8″ (500pc) in diameter, through which beam Roche et al detected the 10 and 20μm fluxes comparable to the IRAS ones.

Markarian 171 is a well known ultra-luminous far-infrared source, as discovered by the Infrared Astronomical Satellite, (IRAS). It is assumed to be undergoing a massive burst of star formation. Our HI observations are part of an effort to determine how merging galaxies might trigger star formation, by careful analysis of the information on the velocity and spatial structure of the gas provided by HI spectral line observations.