Compact Radio Sources and Nuclear Activity in Seyfert Galaxies

Using recent high-resolution radio observations of a large sample of Seyfert galaxies (Roy et al. 1994), we analyze the relations between the compact radio core emission and several nuclear and host galaxy properties. Seyfert nuclei hosted in early-type galaxies or in object with nearby companions show stronger radio cores than the norm. Radio core emission show some correlation with total radio emission and with tracers of nuclear activity (mid-IR, hard X-ray and narrow-line emissions). This favours the view that Seyfert radio cores are powered by AGN rather than by radio supernovae.Comment: 20 pages, latex file with macros included, 7 figures and 6 tables (automatically included

The Local Galaxy Density and the Arm Class of Spiral Galaxies

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 appende

Environmental Effects on Local Active Galactic Nuclei

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.Comment: 16 pages+3 figures, uuencoded postscript file, preprint SISSA 76/94/A , ApJ November 20, 199

The Optical Luminosity Function of Virialized Systems

We determine the optical luminosity function of virialized systems over the full range of density enhancements, from single galaxies to clusters of galaxies. The analysis is based on galaxy systems identified from the Nearby Optical Galaxy (NOG) sample, which is the largest, all-sky catalog of objectively- identified bound objects presently available. We find that the B-band luminosity function of systems is insensitive to the choice of the group-finding algorithms and is well described, over the absolute-magnitude range -24.5 < M < -18.5, by a Schechter function with alpha=-1.4, Mstar=-23.1 and phistar=4.8 10^{-4} Mpc^-3 The characteristic luminosity of virialized systems is ~3 times brighter than that of the luminosity function of galaxies. Our results show that half of the luminosity of the universe is generated in systems with L<2.9 Lstar and that 10% of the overall luminosity density is supplied by systems with L>30 Lstar. We find a significant environmental dependence in the luminosity function of systems, in the sense that overdense regions, as measured on scales of 5 Mpc, preferentially host brighter, and presumably more massive, virialized systems.Comment: Latex, 13 pages, 12 embedded figures (2 bitmapped), ApJ submitted. Full resolution figures available at http://astro.berkeley.edu/~marinon

Structures in Galaxy Clusters

The analysis of the presence of substructures in 16 well-sampled clusters of galaxies suggests a stimulating hypothesis: Clusters could be classified as unimodal or bimodal, on the basis of to the sub-clump distribution in the {\em 3-D} space of positions and velocities. The dynamic study of these clusters shows that their fundamental characteristics, in particular the virial masses, are not severely biased by the presence of subclustering if the system considered is bound.Comment: (16 pages in LATEX, 4 tables in LATEX are at the end of the file, the figures not included are available upon request), REF SISSA 158/93/

Orbit and spin evolution of the synchronous binary stars on the main sequence phase

The sets of the synchronous equations are derived from the sets of non-synchronous equations The analytical solutions are given by solving the set of differential equations. The results of the evolutionary tendency of the orbit-spin are that the semi-major axis shrinks gradually with time: the orbital eccentricity dereacses gradually with time until the orbital circularization; the orbital period shortens gradually with time and the rotational angular velocity of primary component speed up with time gradually before the orbit-rotation achieved the circularization The theoretical results are applied to evolution of the orbit and spin of synchronous binary stars Algol A, B on the main sequence phase The circularization time and life time (age) and the evolutional numerical solutions of orbit and spin when circularization time are estimeted for Algol A, B. The results are discussed and concluded.Comment: 8 pages, accepted for publication in RA