[en] The model of halo-type radio sources in clusters in galaxies is considered, in which this extended structure in the central part of the cluster is formed by remnants of radio galaxies. In this objects, the activity of the parent galaxy has declined, and the main factors influencing the evolution of the radio clouds radiation, due to the effective confinement of these by the thermal pressure of the hot intraclustor gas, are synchrotron and inverse Compton losses. The qualitative analysis and estimates are complemented by computer simulations. The results of the calculations are in a good agreement with the observational data. From general model considerations, some observable features of the halo-type cluster radio sources are predicted as well

[en] A fourth OH megamaser has been found in the luminous IR galaxy Mrk 273 ( = U08696). The characteristics of this masing galaxy are similar to those of the other powerful extragalactic masers in NGC 3690, IC 4553, and Mrk 231. The 1667 MHz line luminosity of Mrk 273 is 335 L. The IR photon to OH photon conversion efficiency is calculated for all OH megamasers and is found to be close to 1%

[en] The purpose of this investigation is to study the possibility that the lack of galaxies in the area between the Virgo and Coma clusters, to which OKROY (1965) drew attention, is due to an intergalactic cloud. Using Zwicky's Catalogue of Galaxies and Clusters of Galaxies, it is shown that there is a shortage of galaxies in the suspected area for all magnitude classes. The absorption of the cloud is calculated to be 0.45+-05 mag. A quantity called the areal colour index (ACI) is introduced and defined as ACI=a sub(b) b sub(b)/(a sub(r) b sub(r)) where a and b are the lengths of the major and minor axes of a galaxy, respectively, and the subscripts b and r respectively refer to measurements on the blue and red prints of the Palomar survey, given in the Uppsala Catalogue of Galaxies. The average ACI is found to be 1.25 for the control area, and 1.04 for the area covered by Okroy's alleged obscuring cloud. On the basis of this colour data an approximate map showing the shape of the cloud is given. The effect of the alleged cloud on the shape frequency of types of galaxies is discussed. It is found that the cloud significantly increases the ratio of elliptical and dwarf galaxies to SO's. The determination of the distance to the cloud and its density is discussed. (author)

[en] A number of issues related to the development of galactic clusters are discussed. The formation of individual galaxies earlier or later than the first contraction of the cluster in which they reside is debated, and the relation of the Hubble type of galaxy to its environment is discussed. The question whether the invisible mass in the universe is attached to individual galaxies or is mostly loose is considered, as well as the question whether such loose matter is located mainly at smaller or larger distances from the cluster center than the galaxies. The possibility that low-mass stars and/or massive neutrinos constitute the invisible matter is discussed. 38 references

[en] High energy observations of the Galactic Center on the subparsec scale seem to be consistent with electron-positron production in the form of relativistic jets. These jets could be produced by a approx.10⁶ M/sub sun/ black hole dynamo transporting pairs away from the massive core. An electromagnetic cascade shower would develop first from ambient soft photons and then non-linearly; the shower using itself as a scattering medium. This is suited to producing, cooling and transporting pairs to the observed annihilation region. It is possible the center of our galaxy is a miniature version of more powerful active galactic nuclei that exhibit jet activity. 15 references, 1 figure

[en] Multi-aperture JHKL colours on the new SAAO photometric system are presented for samples of Seyfert 1, Seyfert 2 and HII-region galaxies. Comparisons are made with the colours of 'ordinary' galaxies obtained using the same system. From the tightness of their distribution in the infrared 2-colour diagrams, Seyfert 1s are inferred to be a relatively homogeneous group whose colours can be explained by the addition of nuclei with power-law spectral distributions to ordinary background galaxies. HII region galaxies are like ordinary ones affected to some degree by high dust content. Seyfert 2s form an intermediate category, in some cases being like Seyfert 1s with obscuration and in others being like HII galaxies. (author)

[en] The intensities of [SIII]lambdalambda9069, 9532 in the nucleus of the classic Liner elliptical galaxy NGC1052 have been measured. Their strength favours photoionization as opposed to shock-heating models, which is in agreement with recent [OIII] electron temperature data for NGC1052 and with [SIII] data for some other Liners. (author)

[en] In order to understand the implications of the apparently high abundance of long polyynes in the ISM, some molecules which are closely related chemically are being studied. A radio search for 1-cyanobut-3-ene-1-yne, CH₂=CH-Ctriple bondC-Ctriple bondN, which is very closely related to HCtriple bondC-Ctriple bondC-Ctriple bondN, the first polyyne to be detected, has yielded an upper limit to the abundance. The data suggest that the chemical processes which give rise to interstellar molecules are biased towards the production of highly unsaturated organic species. The implication of this and other results is discussed with regard to the chemistry of the ISM and future investigations of these important processes. (author)

[en] Rapidly cooling gas is commonly found near the centres of clusters of galaxies. The structure of the resulting gas flows is reviewed. Total gas cooling rates of several hundred solar mass per yr have been observed in a number of cases. Thermal instability and the ultimate fate of the cooled gas are discussed. The cooled gas could easily have formed a massive central galaxy. 25 references

[en] Based on spectrophotometric data, by decomposition of the observed continuum, the power-law continuum characteristics of the central source are obtained. The behavior of both electron temperature and density in the Narrow-Line Region (NLR) of NGC 7469 is discussed on the basis of thermal and ionization equilibria calculations. The electron temperatures in NLR of the Sy1 galaxies are higher than the Sy2 ones. A possible explanation is the lack of a dense zone close to the central source in the Sy2 galaxies. 13 references