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The method of combining several negatives together is at last coming into use. Forty years ago this method was used for the first time by Leontovsky in Leningrad. Putting together many negatives he was able to do photometry of M31 to fainter magnitudes than was possible photoelectrically. the method of preliminary baking of emulsions is more effective when it is done in a nitrogen atmosphere and still better in hydrogen. Spectacular results with the last method were obtained by A. Smith (1977). With a 70m exposure on IIIa-J plates there are no traces of the planetary nebula the Helix. After hydronization the same exposure reveals the overexposed image of this object. Arp and Lorre (1976) obtained striking results on IIIa-J emulsions using the process of deconvolution which improves the negatives. By means of some kind of filtration, removing faint stars and those of medium brightness etc., they improved the resolution of the extended images and obtained a better contrast. the authors published their photographs of the Stefan group and of the jet in M87. As a result of deconvolution it becomes evidence that NGC 7320 is much nearer to us than its apparent neighbouring galaxies because it is clearly resolved into HII regions and star clusters.
During recent years the problem of the virial paradox has grown less acute for many galactic systems, especially for those having few members. As an example one can take the revision of virial mass-to-luminosity ratio, f = M/L, for de Vaucouleurs' groups performed by Materne and Tammann (1974). the reduction of the f-estimate is due to various reasons: an increase in accuracy in measuring radial velocities of galaxies, especially noticeable for 21-cm surveys of groups (Fisher and Tully 1975), regard for the sub-structure of systems of galaxies and improved exclusion of accidental members of groups (referred to here as “optical” members). Some very scattered systems proved to be low-contrast fluctuations of the expanding background, and not physical groups in their usual sense.
Galaxies occur in a wide variety of systems ranging from binary pairs through small groups to rich clusters. These systems in turn possess a wide range of densities, with typical separations between bright (L ≫ L* = 3.4 × 1010 L⊙) galaxies varying from ≲ 10 kpc up to ~ 1 Mpc. Among the most common of these systems are small, loose groups containing ≲ 10 bright galaxies with separations ≳ 100 kpc. Such systems probably contain a substantial fraction of all galaxies (de Vaucouleurs 1975; van den Bergh 1962; Karachentseva 1973). Familiar examples include the Local Group and M81 group.
To date, our view of the universe has largely been two-dimensional. Velocity data, the basis for a look in the third dimension, have been too incomplete and uneven in quality to provide a clear picture. Nonetheless, the pioneering work by de Vaucouleurs (1975) has given us a rough idea of what the universe is like locally. At least a good fraction of galaxies are improbably close to their nearest neighbours compared with expectations based on statistical fluctuations of a random distribution. Our vocabulary to describe these associations includes the words: binary, group, cloud, cluster and supercluster. Does the real universe indeed have characteristic scales that make these terms meaningful? Or, as Peebles and his co-workers (Davis, Groth & Peebles 1977, and reference therein) would have us believe, is there structure on all scales, at least up to about 15 Mpc? and associated galaxies aside, are there galaxies truly randomly distributed: are there field galaxies? Looking two-dimensionally, it has been possible to arrive at remarkably different conclusions. Turner & Gott (1975) concluded that roughly 40% of all galaxies are randomly distributed while Soneira & Peebles (1977) set an upper limit of 18%. It was roughly this latter figure that de Vaucouleurs (1975) derived with his early look into the third dimension. So we ask: (1) what are the characteristic scales and densities of galaxy associations, and (2) what are the scales and densities of the voids?
High velocity clouds (HVC) of neutral hydrogen in or around our galaxy and the observations of intergalactic HI in the Local group: Magellanic stream (Mathewson et al., 1974, Astrophys. J. 190, p. 291), M 31 (Davies, R.D., 1975, Mon. Not. R. astr. Soc., 170, p. 45P), and in the Sculptor group of galaxies (Mathewson et al., 1975, Astrophys. J. 195, p. L97) motivated us to search for HVC-phenomena in a number of nearby late-type galaxies with the 100 m Effelsberg radio telescope which has a half power beam width of 8.5′ at the wavelength of 21 cm.
We have recently completed a series of N-body simulations of galaxy clustering in an expanding universe (Aarseth, Gott and Turner 1977). the initial conditions and our results concerning galaxy clustering will be summarized by Sverre Aarseth at this meeting. in this paper I would like to tell about the implications of these models for the value of Ω = 8πGρO/3HO2 (where ρO is the present mean density of the universe and HO = 50 km s−1 Mpc−1 is Hubble's constant). in the standard Friedmann models with Λ = 0, Ω > 1 implies that the universe will eventually recollapse while Ω < 1 implies the expansion will continue forever. As discussed in Gott, Gunn, Schramm, and Tinsley (1974), there are a number of theoretical arguments to suggest that even the unseen matter in the universe is clustered the way the galaxies are so that virial mass determinations from groups and clusters and statistical virial theorem methods can provide good estimates of the mean mass density in the universe. We can utilize our N-body simulations to check the accuracy of these techniques.
Several properties of the 131 galaxies known within 9. 1 Mpc are investigated. 88 of these galaxies are concentrated into eight groups, leaving 33 percent of true field galaxies. There are E/S0 and S0 galaxies among the field galaxies; their types must be of cosmogonic origin. the groups have small velocity dispersion which limits the mean mass-to-light ratio for the different types of group galaxies to m/L < 20. Within the supergalactic plane the deviation from an ideal Hubble flow are small: the changes of ΔHO/<HO> with distance and direction are not larger than ten percent; the radial component of the peculiar motion of field galaxies is <25 km s−1. the differential luminosity function of S/Im galaxies is well approximated by a Gaussian with and . the luminosity function of E/S0 galaxies is much flatter with a possible minimum, separating true E's and dwarf ellipticals (Reaves, 1977). the sample galaxies are strongly concentrated toward the supergalactic plane; at a distance of 4 Mpc of the plane the luminosity density drops to half its value. There is also a pronounced luminosity density decrease with increasing distance from the Virgo cluster centre; at a distance of 30 Mpc the density has decreased by more than a factor of 104. the best estimate of the mean luminosity density within a sphere of 30 Mpc radius centered on the Virgo cluster is 1.5 · 108 L⊙ Mpc−3.
A systematic and automatic classification of groups of galaxies has been made only in two dimensions up to now (Turner and Gott, 1976). They investigated the projected density of galaxies at the sky. in this analysis one can correct for foreground and background galaxies and superimposed groups only statistically. the properties of the groups and their member galaxies will often not be recognized correctly. Therefore, a three dimensional analysis is proposed.
A halo surrounding the edge-on Sb giant spiral galaxy NGC 4565 has been detected in the spectral band 3800–8600 A using a new photometric instrument, an annular scanning photometer. the halo is brightest close to the galactic nucleus and decreases in brightness until it reaches a level of 1 part in 1000 of the sky at a galactic radius of 6.1 arc minutes or 43 kpc from the galactic center. Because the scan path of the ASP is circular, this point corresponds to a distance of 34 kpc from the galactic plane. For comparison, the Holmberg radius of NGC 4565 is equal to 7 arc minutes or 50 kpc. Preliminary V-I photometric data indicate that the halo becomes redder with increasing galactic radius, exceeding V-I = 1.9. Based on a variety of possible origins for the light, it is concluded that the light is due to stars.
Mass-to-luminosity ratios of systems of galaxies as derived by different authors have a large scatter from ~ 10 to ~ 200. the observational data used by different authors differ only slightly, so the differences should lie in the treatment of the data. We have found that in most cases < M/L > differences can be explained in the following ways.
Subclustering might help to solve the virial theorem paradox for systems of galaxies by hiding a major part of the potential energy in gravitationally bound subsystems. We have shown (Ozernoy and Reinhardt 1976, Astr. Astrophys., 52, 31) that even in groups of galaxies there is mass segregation, in the sense that bright group members tend to be concentrated towards the centre. Recently Wesson and Lermann (1977, Astrophys. Sp. Sci., 46, 327), realizing the importance of subclustering, proposed a quantitative method for estimating its effect on the stability of systems of galaxies. However, their assumption about the frequency of subsystems of multiplicity n is not in accord with Holmberg's (1962) result. the mean frequency of galaxies in pairs is 0.37 for the Turner and Gott groups (1976) and 0.23 for the de Vauceulours groups (1976), in good agreement with the value of 0.25 required by Holmberg's distribution. Assuming Holmberg's frequency of gravitationally bound subsystems and that they are homogeneously distributed throughout the system, we have for the ratio of the total potential energy of a system of N equal masses Ω to the potential energy calculated in the usual way neglecting subclustering Ωs, Ω/Ωs≈ 1+(Rc)/(<r2>N), if the velocity dispersion <σr2(n)> = constant. Here Rc is the effective radius of the system and <r2> the mean distance of binaries. the assumption σr2(n) = const is reasonable for n ≤ 7, when Holmberg's distribution holds, since σr2(2) = 203 km s−1 according to Karachentsev (1974), and increases to only ≃ 1000 km s−1 for rich clusters. Since Karachentsev's data give an <r2> = 33 kpc for HO = 55 km s−1 Mpc−1, we have Ω/Ωs≈ 4 for groups of galaxies with Rc≈ 1 Mpc and N = 10. Thus it seems that subclustering cannot remove the mass discrepancy for rich clusters and for groups only in moderate cases.
We have obtained large scale photographs or electronographs for 40 pairs containing Markarian galaxies: 6 Markarian-Markarian pairs and 34 Markarian-normal pairs, most of which are physical close pairs with two similar components (here “normal” means with no UV excess).
I would like to comment on very preliminary results concerning the cluster membership of Seyfert galaxies. Two years ago van den Bergh stated in a discussion of the bright classical Seyfert galaxies that these objects were mainly field galaxies. We extend this discussion to about seventy objects in the list of Drs Khachikian and Weedman (Astrophys. J., 192, 581, 1974). By a cross correlation of this list with Dr Abell's catalogue of rich clusters taking account both of the positions in the sky and the distances of the objects, we find only two certain cluster members - the well-known case NGC 1275 in the Perseus cluster and Markarian 298 in the Hercules cluster - and three probable or possible other cluster members. Taking into account the fact that only some fifty objects of Khachikian and Weedman fall within the distance range of the Abell catalogue, we find that only a few per cent of the Seyfert galaxies are members of Abell clusters. Within a factor of two, this percentage is the same as the percentage of cluster galaxies relative to all galaxies. Therefore, this result does not point to a pronounced field membership of the Seyfert galaxies.
In the Astronomical Observatory of the town of Belogradchik a one-channel electrophotometer in the UBV system with pulse counting has been installed at the 60-cm Cassegrain telescope. the photoamplifier used is of the type EMI 6256B (1). With this telescope the author has carried out observations of 80 double galaxies during the period 1974 to the middle of 1977, using the differential method of observation with 3 diaphragms (24″, 54″ and 135″) depending on its diameter.
We have gathered data on U, B,V, K magnitudes, radial velocities, spectra, morphological types, radio-emission, dimensions and other characteristics for 47 pairs of galaxies (Metik and Pronik 1978). the following results were obtained:
Saakian, Petrosian and I have studied the central regions of Markarian galaxies using observations made with the SAO 6-metre telescope and the 2.6 m and 0.5 m telescopes of the Burakan Observatory. in a paper soon to be published, we show that in those galaxies which have strong ultraviolet excesses, i.e. Markarian Galaxies, double or multiple nuclei are found with a significantly greater frequency than they are in ordinary galaxies. This result suggests that these are among the most active nuclei. the photographs in our paper show the 60 examples of double or multiple nuclei found in the first 8 lists of Markarian galaxies.