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 Mass Function of Nearby Galaxy Clusters

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.Comment: 10 pages (2 figures not included, available upon request), LATEX, Ref.SISSA 54/93/

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

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/

Velocity Dispersions of CNOC Clusters and the Evolution of the Cluster Abundance

We present the results of the analysis of the internal velocity dispersions, \sigma_v, for the CNOC sample of distant galaxy clusters, based on an interlopers removal algorithm, which is different from that originally applied by Carlberg et al. (1996, C96). We find that the resulting \sigma_v values are consistent within <10% with the original C96 estimates. This result points in favor of a substantial robustness of currently applied methods for optical studies of the internal cluster dynamics. The resulting distribution of velocity dispersions is used to trace the redshift evolution of the cluster abundance with the aim of constraining the matter density parameter, \Omega_m. We find that constraints on \Omega_m are very sensitive to the adopted value of \sigma_8, as obtainable from the local cluster abundance: as \sigma_8 varies from 0.5 to 0.6 (for Omega_m=1), the best fitting Omega_m varies in the range 0.3-1.0.Comment: 11 pages, 8 figures, 1 table, LateX, uses apj.sty, ApJ, corrected some typo

Recovery of fluctuation spectrum evolution from tomographic shear spectra

Forthcoming large angle surveys are planned to obtain high precision tomographic shear data. In principle, they will allow us to recover the spectra of matter density fluctuation, at various redshift, through the inversion of the expressions yielding shear from fluctuation spectra. This was discussed in previous work, where SVD techniques for matrix inversion were also shown to be the optimal tool to this aim. Here we show the significant improvements obtainable by using a 7 bin tomography, as allowed by future Euclid data, as well as the question of error propagation from shear to fluctuation spectra. We find that the technique is a promising tool, namely for the analysis of baryon physics throug high-l shear spectra and to test the consistency between expansion rate and fluctuation growth.Comment: 22 pages, 10 figure

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

The baryon content of the Universe

The large discrepancy between the amount of baryons that were synthesized in Big-Bang and that we detect at $z=0$ locked in stars inside galaxies and in hot/cold gas in galaxies. goup and clusters, is a well known crucial issue for present day cosmology. It is also thought that this riddle is at the backbone of how the ordinary matter has formed, inside dark potential wells, the structures we see today. Then, it is useful to reprint, by means of this archive, the first (pre- astro-ph era) published work in which the amount of "luminous" baryons was actually and suitably computed and the disagreement with the BBN predictions strongly claimed. This because 12 years after the method and the results are still up-to-date, and above all, people are occasionally found to know only later works (appeared on astro-ph) that were meant to be just (ours or other's) follow ups of the present paper.Comment: 5 page