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Our new formulation of the Spherical Collapse Model (SCM-L) takes into account the presence of angular momentum associated with the motion of galaxy groups infalling towards the centre of galaxy clusters. The angular momentum is responsible for an additional term in the dynamical equation which is useful to describe the evolution of the clusters in the non-equilibrium region which is investigated in the present paper. Our SCM-L can be used to predict the profiles of several strategic dynamical quantities as the radial and tangential velocities of member galaxies, and the total cluster mass. A good understanding of the non-equilibrium region is important since it is the natural scenario where to study the infall in galaxy clusters and the accretion phenomena present in these objects. Our results corroborate previous estimates and are in very good agreement with the analysis of recent observations and of simulated clusters.

We analyse a catalogue of simulated clusters within the theoretical framework of the Spherical Collapse Model (SCM), and demonstrate that the relation between the infall velocity of member galaxies and the cluster matter overdensity can be used to estimate the mass profile of clusters, even though we do not know the full dynamics of all the member galaxies. In fact, we are able to identify a limited subset of member galaxies, the ‘fair galaxies’, which are suitable for this purpose. The fair galaxies are identified within a particular region of the galaxy distribution in the redshift (line-of-sight velocity versus sky-plane distance from the cluster centre). This ‘fair region’ is unambiguously defined through statistical and geometrical assumptions based on the SCM. These results are used to develop a new technique for estimating the mass profiles of observed clusters and subsequently their masses. We tested our technique on a sample of simulated clusters; the mass profiles estimates are proved to be efficient from 1 up to 7 virialization radii, within a typical uncertainty factor of 1.5, for more than 90 per cent of the clusters considered. Moreover, as an example, we used our technique to estimate the mass profiles and the masses of some observed clusters of the Cluster Infall Regions in the Sloan Digital Sky Survey catalogue. The technique is shown to be reliable also when it is applied to sparse populated clusters. These characteristics make our technique suitable to be used in clusters of large observational catalogues.

We study morphology and luminosity segregation of galaxies in groups. We analyze the two catalogs of (∼ 2 x 400) groups which have been identified in the Nearby Optical Galaxy sample, by means of hierarchical and percolation ‘friends-of-friends’ methods. We find that earlier-type (brighter) galaxies are more clustered and lie closer to the group centers, both in position and in velocity, than later-type (fainter) galaxies. Spatial segregations are stronger than kinematical segregations. These effects are generally detected at the ≳3-sigma level, with the exception of morphological segregation in velocity, which is the weakest effect. Our main results are confirmed by the analysis of statistically more reliable groups (with at least five members), and are strengthened by the detection of segregation in both hierarchical and percolation catalogs. Luminosity segregation is shown to be independent of morphology segregation. Our conclusions agree with a continuum of segregation properties of galaxies in systems, from low-mass groups to massive clusters.

We discuss a new criterion to estimate the mass in the outer, non-equilibrium region of galaxy clusters, where the galaxy dynamics is dominated by an overall infall motion towards the cluster centre. In the framework of the spherical infall model the local mean velocity of the infalling galaxies at every radius provides information about the integrated matter overdensity $\delta$. Thus, a well-defined value of the overdensity $\delta_t$ is expected at the turnaround radius $r_t$, i.e. the radius where the Hubble flow balances the infall motion. Within this scenario, we analysed the kinematical properties of a large catalogue of simulated clusters, using both dark matter particles and member galaxies as tracer of the infall motion. We also compared the simulation with analytical calculation performed in the spherical infall approximation, to analyze the dependence of the results on cosmology in spatially flat universe. If we normalize cluster mass profiles by means of the turnaround mass $M_t$ (i.e. the mass within $r_t$), they are consistent with an exponential profile in the whole non-equilibrium region ($0.5\la r/r_t\la 2$). Turnaround radii are proportional to virialization radii ($r_t\simeq 3.5 r_v$), while turnaround masses are proportional to virialization masses, i.e. $M_t\simeq 1.7 M_v$, where $M_v$ is the mass within $r_v$. Actually, the mass evaluated within the turnaround radius is a more exhaustive evaluation of the total mass of the cluster. These results can be applied to the analysis of observed clusters., Comment: 10 pages, 7 figures, 3 tables, accepted for publication in MNRAS

Using extensive and well-defined samples of nearby galaxies, we investigate the environment of the galaxies hosting low-luminosity AGNs. The AGNs hosted in luminous early-type spirals tend to reside in denser small-scale environments (

In our sample of 55 clusters the observational relation between the X-ray temperatures and the (robust) galaxy velocity dispersions, T vs. σ, differs, at a s.l. > 99.97%, from the theoretical isothermal relation where T ∞ σ2.

We study morphology and luminosity segregation of galaxies in loose groups. We analyze the two catalogs of groups which have been identified in the Nearby Optical Galaxy (NOG) sample, by means of hierarchical and percolation ``friends-of-friends'' methods (HG and PG catalogs, respectively). In the first part of our analysis we consider 387 and 436 groups of HG and PG, respectively, and compare morphology- (luminosity-) weighted to unweighted group properties: velocity dispersion, mean pairwise distance, and mean groupcentric distance of member galaxies. The second part of our analysis is based on two ensemble systems, one for each catalog, built by suitably combining together galaxies of all groups (1584 and 1882 galaxies for HG and PG groups, respectively). We find that earlier-type (brighter) galaxies are more clustered and lie closer to the group centers, both in position and in velocity, than later-type (fainter) galaxies. Spatial segregations are stronger than kinematical segregations. These effects are generally detected at the larger than 3-sigma level. Luminosity segregation is shown to be independent of morphology segregation. Our main conclusions are strengthened by the detection of segregation in both hierarchical and percolation catalogs. Our results agree with a continuum of segregation properties of galaxies in systems, from low-mass groups to massive clusters., 12 pages, 8 eps figures, submitted for publication in AA

We compare properties of galaxies in loose groups with those in field environment by analyzing the Nearby Optical Galaxy (NOG) catalog of galaxy systems. We consider as group galaxies, objects belonging to systems with at least five members identified by means of the "friends of friends method", and, as field galaxies, all galaxies with no companions. We analyze both a magnitude--limited sample of 959 and 2035 galaxies (groups vs. field galaxies, respectively, B, Comment: 11 pages, 10 eps figures, A&A in press

We analyze a sample of 105 clusters having virial mass homogeneously estimated and for which galaxy magnitudes are available with a well defined high degree of completeness. In particular, we consider a subsample of 89 clusters with B_j band galaxy magnitudes taken from the COSMOS/UKST Southern Sky Object Catalogue. We compute cluster luminosities L_{B_j} within several clustercentric distances and within the virialization radius R_{vir}. In particular, we use the luminosity function and background counts estimated by Lumsden et al. (1997) on the Edinburgh/Durham Southern Galaxy Catalogue. We analyze the effect of several uncertainties connected to photometric data, fore/background removal, and extrapolation below the completeness limit of the photometry, in order to assess the robustness of our cluster luminosity estimates. We draw our results on the relations between luminosity and dynamical quantities from the COSMOS sample by considering mass and luminosities determined within the virialization radius. We find a very good correlation between cluster luminosity, L_{B_j}, and galaxy velocity dispersion, sigma_v, with L_{B_j} proportional to sigma_v^{2.1--2.3}. Our estimate of typical value for the mass-to-light ratio is M/L_{B_j} about 250 (in solar units). We do not find any correlation of M/L_{B_j} with cluster morphologies, i.e. Rood--Sastry and Bautz--Morgan types, and only a weak significant correlation with cluster richness. We find that mass has a slight, but significant, tendency to increase faster than the luminosity does, M proportional to L_{B_j}^{1.2--1.3}. We verify the robustness of this relation against a number of possible systematics., 18 pages, 6 eps figures, accepted by ApJ

We evaluate in a homogeneous way the optical masses of 170 nearby clusters (z< 0.15). The sample includes both data from the literature and the new ENACS data (Katgert et al. 1996, 1998). On the assumption that mass follows the galaxy distribution, we compute the masses of each cluster by applying the virial theorem to the member galaxies. We constrain the masses of very substructured clusters (about 10% of our clusters) between two limiting values. After appropriate rescaling to the X-ray radii, we compare our optical mass estimates to those derived from X-ray analyses, which we compiled from the literature (for 66 clusters). We find a good overall agreement. This agreement is expected in the framework of two common assumptions: that mass follows the galaxy distribution, and that clusters are not far from a situation of dynamical equilibrium with both gas and galaxies reflecting the same underlying mass distribution. We stress that our study strongly supports the reliability of present cluster mass estimates derived from X-ray analyses and/or (appropriate) optical analyses., 13 pages, 7 eps figures, tables are not included, USE LaTeX2e !!, accepted by ApJ

We analyze the internal structures of clusters A1689 and A2218 by applying a recent development of the method of wavelet analysis, which uses the complete information obtained from optical data, i.e. galaxy positions and redshifts. We find that both clusters show the presence of structures superimposed along the line of sight with different mean redshifts and smaller velocity dispersions than that of the system as a whole, suggesting that the clusters could be cases of the on-going merging of clumps. In the case of A2218 we find an acceptable agreement between our estimate of optical virial mass and X-ray and gravitational lensing masses. On the contrary, in the case of A1689 we find that our mass estimates are smaller than X-ray and gravitational lensing ones at both small and large radii. In any case, at variance with earlier claims, there is no evidence that X-ray mass estimates are underestimated., Comment: 8 pages, 2 eps figures, Use LaTeX2e, accepted by Astrophysical Journal, in press November 1997, Vol.490

We compute the distribution of internal velocity dispersions, a, for a sample of 153 nearby Abell-ACO galaxy clusters (z less than or equal to 0.15), each of which has at least 30 available galaxy redshifts. Throughout our work we applied homogeneous procedures to the analysis of the redshifts of the clusters selected. Previous sigma-distributions, based on smaller cluster samples, are complete for the Abell richness class R greater than or equal to 1. In order to improve sigma completeness, we enlarge our sample by including also poorer clusters. By resampling our 153 clusters, according to the richness class frequencies of the Edinburgh-Durham Cluster Catalog (EDCC), we obtain a cluster sample which can be taken as representative of the nearby Universe. Our cumulative sigma-distribution agrees with previous distributions within their sigma completeness limit (sigma greater than or equal to 800 km s(-1)). We estimate that our distribution is complete for at least sigma greater than or equal to 650 km s(-1). In this completeness range, a fit of the form dN alpha sigma(alpha)d sigma gives alpha = -(7.4(-0.8)(+0.7)), in fair agreement with results coming from the X-ray temperature distributions of nearby clusters.

We analyze the presence of substructures in a set of 48 galaxy clusters by using galaxy positions and redshifts. The data are taken from literature sources, with the addition of some new data provided by recent observations of galaxy clusters. We use a multiscale analysis that couples kinematical estimators with the wavelet transform. With respect to previous works, we introduce three new kinematical estimators. These estimators parameterize the departures of the local means and/or local dispersions of the measured radial velocities with respect to their global values for the environment. We classify the analyzed clusters as unimodal, bimodal, and complex systems. We find that about 14% of our clusters are strongly substructured (i.e., they are bimodal or complex) and that about 24% of the remaining unimodal clusters contain substructures at small scales. Thus, in substantial agreement with previous studies, about one-third of clusters show substructures. We find that the presence of substructures in unimodal clusters does not affect the estimates of both velocity dispersions and virial masses. Moreover, the galaxy velocity dispersion is generally in good agreement with the X-ray temperature, according to the expectations of the standard isothermal model for galaxy clusters. These facts suggest that unimodal clusters, which are the most frequent cases in the nearby universe, are not too far from a status of dynamical equilibrium. In contrast, the estimates of velocity dispersions and masses for some bimodal or complex clusters strongly depend on whether they are treated as single systems or as sums of different clumps. In these cases the X-ray temperature and the velocity dispersion may be very different.

Using a large and well-controlled sample of clusters of galaxies, we investigate the relation between cluster velocity dispersions and X-ray temperatures of intra-cluster gas. In order to obtain a reliable estimate of the total velocity dispersion of a cluster, independent of the level of anisotropies in galaxy orbits, we analyze the integrated velocity dispersion profiles over increasing distances from the cluster centers. Distortions in the velocity fields, the effect of close clusters, the presence of substructures, and the presence of a population of (spiral) galaxies not in virial equilibrium with the cluster potential are taken into account. Using our final sample of 37 clusters, for which a reliable estimate of the velocity dispersion could be obtained, we derive a relation between the velocity dispersions and the X-ray temperatures, with a scatter reduced by more than 30 % with respect to previous works. A chi square fit to the temperature-velocity dispersion relation does not exclude the hypothesis that the ratio between galaxy and gas energy density (the so-called spectral beta) is a constant for all clusters. In particular, the value of beta=1, corresponding to energy equipartition, is acceptable., 13 pages, uuencoded gzipped postscript file, fig.1 available upon request, to appear in ApJ on 20th December 1995, corrected misprint in table 5

We analyze the internal velocity dispersions of a sample of 172 nearby galaxy clusters (z < 0.15), each of which has at least 30 available galaxy redshifts, and spans a large richness range. Cluster membership selection is based on nonparametric methods. In the estimate of galaxy velocity dispersion we consider the effects of possible velocity anisotropies in galaxy orbits, the infall of late-type galaxies, and velocity gradients. The dynamical uncertainties due to the presence of substructures are also taken into account. Our cumulative distribution agrees with previous distributions within their completness in velocity dispersion ( > 800 km/s). We estimate that our distributions is complete for at least a dispersion greater than 650 km/s. In this completeness range a power law fit is in fair agreement with results coming from the X-ray temperature distributions., 18 pages, latex file with macros included, 9 figures and 6 tables (automatically included), ApJ in press

We analyze the density profiles and virial radii for a sample of 90 nearby clusters, using galaxies with available redshifts and positions. Each cluster has at least 20 redshifts measured within an Abell radius, and all the results come from galaxy sets of at least 20 members. Most of the density profiles of our clusters are well fitted by hydrostatic-isothermal-like profiles. The slopes we find for many cluster density profiles are consistent with the hypothesis that the galaxies are in equilibrium with the binding cluster potential. The virial radii correlate with the core radii at a very high significance level. The observed relationship between the two size estimates is in agreement with the theoretical one computed by using the median values of the density profile parameters fitted on our clusters. After correcting for incompleteness in our cluster sample, we provide the universal distributions functions of core and virial radii (obtained within half an Abell radius)., 28 pages, LateX file, to appear in ApJ, preprint SISSA ref 77/94/A

Relying on samples of disk galaxies for which a detailed photometric bulge/disk decomposition has been provided in the literature, we examine the dependence of the bulge-to-disk luminosity ratio (B/D) on the blue absolute luminosity and on the environmental density. In our statistical analysis of various B/D data sets we pay particular attention to disentangling the role played by the galaxy morphology--galaxy density relation. Besides, we focus our attention on nearby ($z, LATEX file, 19 pages, figures available on request

The dependence of the luminosity function of cluster galaxies on the evolutionary state of the parent cluster is still an open issue, in particular as concern the formation/evolution of the brightest cluster galaxies. We plan to study the bright part of the LFs of a sample of very unrelaxed clusters ("DARC" clusters showing evidence of major, recent mergers) and compare them to a reference sample of relaxed clusters spanning a comparable mass and redshift range. Our analysis is based on the SDSS DR7 photometric data of ten, massive, and X-ray luminous clusters (0.2, Comment: 11 pages, 12 figures and 9 tables

We have examined the effect of the environmental density on the arm classification of an extensive sample of spiral galaxies included in the Nearby Galaxy Catalog (Tully, 1988a). We have also explored the dependence of the arm class of a galaxy on other factors, such as its blue absolute magnitude and its disk-to-total mass ratio, inferred in the literature either from the gradient of a good galaxy rotation curve or from a photometric mass decomposition method. We have found that the arm class is strongly related to the absolute magnitude in the mid-type spirals (in the sense that grand design galaxies are, on average, more luminous than flocculent objects), whilst this relation is considerably weaker in the early and late types. In general the influence of the local density on the arm structure appears to be much weaker than that of the absolute magnitude. The local density acts essentially in strengthening the arm class--absolute magnitude relation for the mid types, whereas no environmental density effects are observed in the early and late types. Using the most recent estimates of the disk-to-total mass ratio, we do not confirm this ratio to be a significant factor which affects the arm class; nevertheless, owing to poor statistics and large uncertanties, the issue remains open. Neither a local density effect nor an unambiguous bar effect on the disk-to-total mass ratio is detectable; the latter finding may challenge some theoretical viewpoints on the formation of bar structures., Comment: 15 pages, Latex, SISSA 102/93/A openbib.sty and 4 POSTSCRIPT figures appended

Using an extensive sample of nearby galaxies (the Nearby Galaxies Catalog, by Tully), we investigate the environment of the galaxies hosting low-luminosity AGNs (Seyferts and LINERs). We define the local galaxy density, adopting a new correction for the incompleteness of the galaxy sample at large distances. We consider both a complete sample of bright and nearby AGNs, identified from the nuclear spectra obtained in available wide optical spectroscopic surveys, and a complete sample of nearby Seyferts. Basically, we compare the local galaxy density distributions of the AGNs with those of non-AGN samples, chosen in order to match the magnitude and morphological type distributions of the AGN samples. We find, only for the early-type spirals more luminous than $\sim M^*$, that both LINERs and Seyferts tend to reside in denser environments on all the scales tested, from tenths of Mpc to a few Mpc; moreover Seyferts show an enhanced small-scale density segregation with respect to LINERs. This gives support to the idea that AGNs can be stimulated by interactions. On larger scales, tens of Mpc, we find that the AGNs hosted in luminous early-type spirals show a tendency to stay near the center of the Local Supercluster. Finally we discuss the interpretations of our findings and their consequences for some possible scenarios of AGN formation and evolution and for the problem of how AGNs trace the large-scale structures., 16 pages+3 figures, uuencoded postscript file, preprint SISSA 76/94/A , ApJ November 20, 1994

Using a variety of parameters of local galaxy density, we have examined the effects of the environmental density on the presence of bar structures in spiral galaxies of various morphological types. For an extensive sample of nearby galaxies, listed in the ``Nearby Galaxies Catalogue'' (Tully, 1988a), we have found that the spirals characterized by a high local density tend to be barred if they are early-type and early-type if they are barred (at the significance level of $\sim$3 sigma), confirming some earlier suggestion of low statistical significance. This fact, which is observed substantially in low-luminosity spirals, indicates that galaxy interactions can stimulate the formation of bars, primarily in early-type, low-luminosity spirals. This is in partial, qualitative agreement with the most recent relevant N-body simulations. On the other hand, no significant density segregation is observed between pure S-shaped (S(s)) spirals and spirals with inner rings (S(r)), which are often associated with bars. {\it Subject headings:} galaxies: general --- galaxies: structure --- galaxies: interactions --- galaxies: clustering, Comment: 23 pages, LaTeX, SISSA Ref. 178/92/A

While looking for the fundamental parameters of spiral galaxies, Whitmore (1984, hereafter W84), discovered a correlation between the arm structures and the gradients of the rotation curve: the Outer Gradient (OG) was shown to increase with increasing DDO class (van den Bergh 1960), for a sample of ~ 30 galaxies. This result was in contradiction with the previous one by Kormendy and Norman (1979), but consistent with the prediction of the density wave theory (Lin and Shu 1964) that the higher is the fraction of the total mass in the disk (i.e. the lower the gradient of the rotation curve), the better defined and developed are the spiral arms (see, e.g., Toomre 1981, Carlberg and Freed-man 1985). In this work, we have re-addressed this issue using a much larger sample of 94 galaxies, and well defined parameters for the gradients of the rotation curves and the arm morphology. Our results support W84, and hence, the density wave theory. A recent work by Elmegreen and Elmegreen (1990; hereafter EE90), yielded similar results as ours, although for a much smaller sample of galaxies (41).

In the last few years, considerable effort has been devoted to outlining the possible correlations of the galaxy properties with local density. The tightness of the relationship between luminosity and the absolute diameters of galaxies (hereafter referred to as L-D relation) suggests that possible environmental effects should be detectable from the analysis of its shape in different samples. However, Aguilar and White (1986) predicted that the tidal truncation should have a hardly detectable effect on the galaxy isophotal diameter. Peterson et al. (1979) found the Virgo disk galaxies appeared to have smaller diameters than the Hercules disk galaxies. Giuricin et al. (1985) found L-D relations with shallower slopes in samples of spirals located in higher compactness groups. Giuricin et al. (1988) found differences in the L-D relation for disk galaxies in some clusters; but they did not find a dependence of the L-D relation on any cluster properties.

An excess of higher redshift galaxies, relative to the brightest member, in loose groups, was discovered by Arp in 1970, and was later confirmed by several authors. This effect is found to be present also in nearby small groups, identified by Tully in the Nearby Galaxy Catalogue. The asymmetry found is not likely to be ascribed to contamination by interlopers. A significant anticorrelation has also been found between the color excess E(B-V)(0)T and the velocity difference, with an associated E(B-V)(0)T variation on the order of 0.1-0.2. Such anticorrelation is not induced by obvious selection effects, such as the color-magnitude relation. A possible explanation is that groups are still collapsing and contain diffuse dust in the intragroup medium, with a mean optical depth, in the blue bland, on the order of 0.1-0.2. The mean dust density inside groups would be about 4 x 10 exp -31 g/cu cm; if the presence of dust is not only a local effect, the deduced cosmological density Omega(dust) would be in the range 10 exp -4 to 10 exp -5.

A statistical analysis of the soft X-ray emission from spiral galaxies with normal and low-luminosity active nuclei (LINERs and Seyfert 2), derived from published observations obtained with the Einstein Observatory, has revealed a number of previously unrecognized characteristics of the X-ray emission. Seyfert 2 galaxies turn out to be, on average, stronger X-ray emitters (per unit light) than non-Seyfert galaxies, whereas galaxies with LINER nuclei and H II-region-like nuclei exhibit X-ray emissions of comparable strength.

We have analyzed existing data on colours and Tully-Fisher distances of a sample of spiral galaxies in the Virgo cluster. The data seem to indicate a significant correlation between the colour-excesses and distances of these galaxies. This correlation may be due to extinction by intracluster (IC) dust. However, due to uncertainties in the observational data, and the limited size of the sample, such an interpretation may not yet be construed as an unequivocal evidence for dust in the Virgo cluster of galaxies.

The asymmetric distribution of galaxy redshifts in some nearby-group samples is explained as due to the existence of intragroup dust. The existence of a correlation between color excess of galaxies and radial velocity supports the hypothesis made.

An excess of higher redshift galaxies, relative to the brightest member in loose groups, was discovered by Arp (1970, and later confirmed by several authors). We find this effect to be present also in nearby small groups identified by Geller and Huchra (1983) in the Center for Astrophysics Survey.

We examine the 10 microns emission of the central regions of 117 Seyfert galaxies, after having compiled all the ground-based, small aperture (˜5") photometric observations at lambda ˜ 10 microns (N-magnitudes) published in the literature. We also evaluate the compactness of the 10 microns emission through a comparison of these small-beam measures with the large beam IRAS 12 microns fluxes. We apply survival analysis statistical techniques in order to exploit the information contained in "censored" data (i.e., upper limits on fluxes). Seyfert galaxies appear to have more compact and powerful central 10 microns emission than non-Seyfert galaxies have. Interactions do not affect appreciably the 10 microns emission of Seyfert galaxies. Their 10 microns emission, which is quite weakly related to the X-ray emission, correlates well with the nuclear non-stellar near-infrared emission and with the IRAS 12 and 25 microns band emissions, less well with the IRAS 60 microns emission and even worse with the IRAS 100 microns emission. The 100 microns to 25 microns global energy distribution flattens systematically with increasing 10 microns luminosity. Seyferts 1 have, on average, greater 10 microns luminosity than S2 have, but similar surface brightness and compactness. Seyferts 2 have steeper continuum spectra between 12 and 25 microns than Seyferts 1 have. Our results favour thermal dust emission models for the origin of the mid-infrared emission of Seyfert galaxies. Within the context of unified schemes of Seyfert galaxies, our findings support the presence of a moderate amount of anisotropy in the 10 microns emission and are consistent with the presence of Thomson optically thin obscuring dust tori around Seyfert nuclei.

We present the distribution of virial masses for nearby galaxy clusters, as obtained from a data-set of 75 clusters, each having at least 20 galaxy members with measured redshifts within 1 Abell radius. After having accounted for problems of incompleteness of the data-set, we fitted a power-law to the cluster mass distribution., 10 pages (2 figures not included, available upon request), LATEX, Ref.SISSA 54/93/A

The velocity field of galaxies in clusters is investigated on the basis of a sample consisting of 68 clusters with at least 30 galaxies for which redshifts are available in the literature; for 61 of these clusters, most of the galaxy magnitudes were collected. Galaxies brighter than the magnitude of the third-ranked object, m3, have velocities lower than average. These galaxies are preferentially located in the central regions. The effect is not induced by morphological segregation, it is not restricted to cD clusters, and it does not depend on the presence of substructures. The energy equipartition status seems to be achieved by these low-velocity galaxies. This evidence of segregation stresses the importance of m3 as a boundary between different dynamical statuses, and constrains the theory of structure and evolution of clusters of galaxies. A possible interpretation is given in terms of dynamical friction and merging.

Several samples of disk galaxies have been collected in order to study, in each of them, the relation between the blue total corrected absolute magnitude and the absolute corrected isophotal diameter. These luminosity-diameter relations have been compared to detect a possible dependence on the density of the galaxy environment. No significant differences have been found among the several relations, especially if selection criteria relative to the various samples are taken into account. This result is in disagreement with several previous claims. 61 refs.

We have examined a sample of ∼150 elliptical galaxies taken from a recent survey (Bursteinet al., 1987) which includes also new CCD photometric data. The fits of total luminosityL versus three different diameter indicators (i.e., the effective diameterDe, theDn diameter proposed by Dressleret al. (1987), and the isophotal diameterD0 at 25 mag arc sec−2) had given no sign of environmental effect on such quantities. A comparison with previous results based on lower quality data was carried out in order to check the reliability of different photometries and statical tools used.

We have compared the radio continuum emission of three samples of bright (Bto

An investigation of the radio continuum properties of the spiral galaxies which have been classified in the Elmegreen and Elmegreen (1987) arm morphology system reveals no difference in the radio continuum emission (per light unit) for flocculent and grand design spirals. Nor is the X-ray emission (per light unit) of the two classes of spirals different. Furthermore, we find that flocculent galaxies are more frequently encountered in samples of interacting and binary galaxies than among relatively isolated objects.

The aim of this work is to analyze the variation with distance of the values of the classical parameters of galaxy clusters (i.e.: total luminosity L, velocity dispersion V, virial radius R, virial mass M, and mass-to-light ratio M/L), to investigate on possible systematic effects.

Wir haben das Modell von Wood (1972) benutzt, um die lichtelektrischen Beobachtungen von Cerruti-Sola und Scaltriti (1980) des Bedeckungsveranderkuchen BB Peg wiederzuanalysieren. Die photometrischen Elementen, die wir errechnet haben, sind bedeutend verschieden von den vorlaufigen Elementen, die vorher bekanntgegeben worden sind. Unsere Elementen zeigen, das BB Peg ein Kontaktdoppelstern ist, dessen im primaren Minimum bedeckte Komponente kleiner als die andere ist. BB Peg folgt den allgemeinen Eigenschaften der W UMa Typus W Sterne. Using Wood's (1972) model we have reanalyzed Cerruti-Sola and Scaltriti's (1980) photoelectric observations of the eclipsing binary BB Peg. Our photometric elements, which turn out to be considerably different from the earlier preliminary results, describe BB Peg as a contact system, in which the component eclipsed at the deeper minimum is smaller than its companion. BB Peg appears to conform to the general properties of the W-type subclass of W UMa systems.

Seven-colour photoelectric light curves-as yet unsolved-of the single-lined spectrum eclipsing binary HR 9049 (Burki and Rufener, 1980) have been analysed by means of Wood's (1972) model. HR 9049 appeared to be composed of two normal Main-Sequence detached components having appreciably different temperatures, sizes and luminosities. The hotter star, classed approximately as B6 V, is larger and brighter than its cooler companion, for which a spectral type around A5 can be inferred.

The study of the relations between the radio continuum emission of spirals and other global properties (e.g.HI content, colours, Hα emission strengths, infrared emission, arm classification), which are know to be probably different in different environments, can be of aid in understanding the nature of the radio continuum emission. In the present study we examine a sample of nearby spirals (V0 < 3000Km/s).

The extensive survey of photometric data of Burstein et al. (1987) are used to reexamine the luminosity-size relation of about 160 elliptical galaxies belonging to different regions in order to search for possible dependence of this relation on the galaxy environment. For each galaxy, the total blue luminosity, the isophotal diameter, the effective diameter, and the diameter within which a galaxy has a mean surface brightness of 20.75 M mag/sq arcsec are considered. The ellipticals of the Virgo, Coma, and Perseus clusters which are located in the inner and outer cluster regions are separately considered. No significant differences are found in various linear relations relative to different subsamples of ellipticals located in different environments. It is concluded that the data base of Burstein et al. gives no signatures of appreciable environmental effects on the luminosity-size relations of ellipticals. 32 refs.

We present a method capable of determining the evolutionary stage of bound, isolated systems of galaxies. In particular, we shall apply it to a sample of groups, belonging to the Local Supercluster, taken from the Geller and Huchra’s (1983) Catalogue. The knowledge of the evolutionary stage of a system of galaxies is interesting in the framework of theories concerned with the formation of large-scale structures in the universe. Moreover, if one knows the evolutionary stage, it is possible, at least in principle, to determine the mass of the system even when it is not in virial equilibrium, as well as to infer some properties of its initial condition.

We have investigated the luminosity distributions of the first-ranked, second-ranked, and third-ranked cluster galaxies for different cluster morphological types. Basically, we have found that the two magnitude distributions relative to the cD, B and C, L, F, I clusters (according to Rood and Sastry’s classification) differ significantly for the first-ranked members, whereas they are not significantly different for the second- and third-ranked members. This fact points to some differences in the creation mechanism or evolutionary processes relative to the first-ranked members of the cD, B and C, L, F, I clusters.