Papers by marino mezzetti
Forthcoming experiments will enable us to determine high precision tomographic shear spectra. Mat... more Forthcoming experiments will enable us to determine high precision tomographic shear spectra. Matter density fluctuation spectra, at various z, should then be worked out of them, in order to constrain the model and determine the DE state equation. Available analytical expressions, however, do the opposite, enabling us to derive shear spectra from fluctuation spectra. Here we find the inverse expression, yielding density fluctuation spectra from observational tomographic shear spectra. The procedure involves SV D techniques for matrix inversion. We show in detail how the approach works and provide a few examples.
The Astrophysical Journal, 2015
We study the effects of sample variance in N-body simulations, as a function of the size of the s... more We study the effects of sample variance in N-body simulations, as a function of the size of the simulation box, namely in connection with predictions on tomographic shear spectra. We make use of a set of 8 ΛCDM simulations in boxes of 128, 256, 512 h −1 Mpc aside, for a total of 24, differing just by the initial seeds. Among the simulations with 128 and 512 h −1 Mpc aside, we suitably select those closest and farthest from average. Numerical and linear spectra P (k, z) are suitably connected at low k so to evaluate the effects of sample variance on shear spectra C ij () for 5 or 10 tomographic bands. We find that shear spectra obtained by using 128 h −1 Mpc simulations can vary up to ∼ 25 %, just because of the seed. Sample variance lowers to ∼ 3.3 %, when using 512 h −1 Mpc. These very percentages could however slightly vary, if other sets of the same number of realizations were considered. Accordingly, in order to match the ∼ 1 % precision expected for data, if still using 8 boxes, we require a size ∼ 1300-1700 h −1 Mpc for them.
The Astrophysical Journal, 1998
We evaluate in a homogeneous way the optical masses of 170 nearby clusters (z ≤ 0.15). The sample... more 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.
Large Scale Structures of the Universe, 1988
Observational Evidence of Activity in Galaxies, 1987
Observational Cosmology, 1987
Our examination of the absolute luminosities and sizes of /+* 500 lenticular and spiral members o... more Our examination of the absolute luminosities and sizes of /+* 500 lenticular and spiral members of several clusters has revealed appreciable differences in the galaxy luminosity-diameter relationships for different clusters.
We analyze the presence of substructures in a set of 48 galaxy clusters, by using galaxy position... more We analyze the presence of substructures in a set of 48 galaxy clusters, by using galaxy positions and redshifts. We use a multi-scale analysis which couples kinematical estimators with the wavelet transform. 14% of our clusters are strongly substructured (i.e. they are bimodal or complex) and 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. In unimodal clusters the presence of substructures does not affect the estimates of both virial masses and velocity dispersions, which are generally in good agreement with the X-ray temperatures. Thus, unimodal clusters are not too far from a status of dynamical equilibrium. On the contrary, 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 and X-ray temperatures and velocity dispersions may be very different.
We use the two-point correlation function in redshift space, xi(s), to study the clustering of th... more We use the two-point correlation function in redshift space, xi(s), to study the clustering of the galaxies and groups of the Nearby Optical Galaxy (NOG) Sample, which is a nearly all-sky, complete, magnitude-limited sample of ~ 7000 bright and nearby optical galaxies. The correlation function of galaxies is well-described by a power-law, xi(s)= (s/s0)-gamma, with gamma ~ 1.5 and s0~ 6.4; h-1 Mpc. We find evidence of morphological segregation between early- and late-type galaxies, with a gradual decreasing of the strength of clustering from the S0 to the late-type spirals, on intermediate scales. Furthermore, luminous galaxies (with MB<= -19.5 + 5 log h) are more clustered than dim galaxies. The groups show an excess of clustering with respect to galaxies. Groups with greater velocity dispersions, sizes, and masses are more clustered than those with lower values of these quantities.
The Astrophysical Journal, 1997
The Astrophysical Journal, 1993
We present the distribution of virial masses for nearby galaxy clusters, as obtained from a data-... more 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 1.5 h −1 Mpc. After having accounted for problems of incompleteness of the data-set, we fitted a power-law to the cluster mass distribution.
The Astrophysical Journal, 1994
Using an extensive sample of nearby galaxies (the Nearby Galaxies Catalog, by T ully), we i n v e... more Using an extensive sample of nearby galaxies (the Nearby Galaxies Catalog, by T ully), we i n v estigate the environment of the galaxies hosting low-luminosity A GNs (Seyferts and LINERs). We dene 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 A GNs, identied from the nuclear spectra obtained in available wide optical spectroscopic surveys, and a complete sample of nearby Seyferts. Basically, w e 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 nd, only for the early-type spirals more luminous than 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 i n teractions. On larger scales, tens of Mpc, we nd 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 ndings and their consequences for some possible scenarios of AGN formation and evolution and for the problem of how A GNs trace the largescale structures.
The Astrophysical Journal, 1996
Using a large and well-controlled sample of clusters of galaxies, we i n v estigate the relation ... more Using a large and well-controlled sample of clusters of galaxies, we i n v estigate the relation between cluster velocity dispersions and X-ray temperatures of intra-cluster gas. The cluster selection is based on nonparametric methods. In particular, we present the 2-D optical maps of our sample clusters, obtained via the kernel adaptive technique, using an optimized smoothing parameter. 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 proles over increasing distances from the cluster centers. Both increasing and decreasing integrated proles are found, but the general trend is a attening of the integrated velocity dispersion prole at the largest radii, thus enabling us to take the asymptotic value of the integrated prole as an estimate of the total velocity dispersion which is independent of possible anisotropies. Distortions in the velocity elds, the eect 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 for reducing the errors in the estimate of the cluster velocity dispersions. Using our nal 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 2 t to the temperature-velocity dispersion relation does not exclude the hypothesis that the ratio between galaxy and gas energy density (the so-called spec) is a constant for all clusters. In particular, the value of spec = 1, corresponding to energy equipartition, is acceptable. However, the large data scatter in-T relation may suggest the presence of intrinsic dispersion. This intrinsic dispersion may be due to spurious eects (we consider the eect of cluster ellipticity), as well as to physical reasons, dierent v alues of spec pertaining to clusters with dierent properties.
The Astrophysical Journal, 1996
We analyze the internal velocity dispersion, σ, of a sample of 172 nearby galaxy clusters (z≤ 0.1... more We analyze the internal velocity dispersion, σ, 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. Previous σ-distributions, based on smaller cluster samples, are complete for the Abell richness class R ≥ 1. In order to improve σ completeness, we enlarge our sample by including also poorer clusters. By resampling 153 Abell-ACO clusters, according to the richness class frequencies of the Edinburgh-Durham Cluster Catalog, we obtain a cluster sample which can be taken as representative of the nearby Universe. Our cumulative σ-distribution agrees with previous distributions within their σ completeness limit (σ ∼ > 800 km s −1). We estimate that our distribution is complete for at least σ ≥ 650 km s −1. In this completeness range, a fit of the form dN ∝ σ α dσ gives α = −(7.4 +0.7 −0.8), in fair agreement with results coming from the X-ray temperature distributions of nearby clusters. We briefly discuss our results with respect to σ-distributions for galaxy groups and to theories of large scale structure formation.
The Astrophysical Journal, 1998
We present a new determination of the mass function of galaxy clusters, based on optical virial m... more We present a new determination of the mass function of galaxy clusters, based on optical virial mass estimates for a large sample of 152 nearby (z ≤ 0.15) Abell-ACO clusters, as provided by Girardi et al. (1998). This sample includes both data from the literature and the new ENACS data. The resulting mass function is reliably estimated for masses larger than M lim 4 × 10 14 h −1 M , while it is affected by sample incompleteness at smaller masses. We find N (> M lim) = (6.3 ± 1.2) 10 −6 (h −1 Mpc) −3 for cluster masses estimated within a 1.5 h −1 Mpc radius. Our mass function is intermediate between the two previous estimates by Bahcall & Cen (1993) and by Biviano et al. (1993). Based on the Press-Schechter approach, we use this mass function to constrain the amplitude of the fluctuation power spectrum at the cluster scale. After suitably convolving the PS predictions with observational errors on cluster masses and COBE-normalizing the fluctuation power spectrum, we find σ 8 = (0.60 ± 0.04)Ω −0.46+0.09Ω0 0 for flat low-density models and σ 8 = (0.60 ± 0.04)Ω −0.48+0.17Ω0 0 for open models (at the 90% c.l.).
The Astrophysical Journal, 1995
The Astrophysical Journal, 1994
We have examined the effect of the environmental density on the arm classification of an extensiv... more 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 diskto-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.
The Astrophysical Journal, 1996
Using recent high-resolution (<0.1") radio observations of a large sample of Seyfert galaxies (Ro... more Using recent high-resolution (<0.1") radio observations of a large sample of Seyfert galaxies (Roy et al., 1994), we analyze the relations between their compact radio core emission and several nuclear and host galaxy properties (galaxy morphology, optical, infrared, X-ray, extended radio emissions, interaction parameters, and some emission line properties). We apply survival analysis techniques in order to exploit the information contained in the numerous "censored" data (upper limits on fluxes). We find that Seyfert nuclei hosted in early-type galaxies are, on average, characterized by stronger radio core emission than the norm for Seyfert galaxies. Galaxies with a nearby companion display enhanced radio core emission with respect to objects without companions. Furthermore, we confirm that Seyfert types 2 host more powerful compact radio cores than types 1. Remarkably, radio core emission appears to be unrelated to optical, near-infrared, and far-infrared radiations, but shows some correlation with total radio emission and with tracers of nuclear activity such as the IRAS 12 and 25 µm band, hard X-ray and narrow-line emissions. This favours the view that Seyfert radio cores are typically powered by AGN rather than by radio supernovae. A link between radio core strength and bolometric luminosity is suggested, in analogy to what is observed in the cores of radio-quiet QSOs.
The Astrophysical Journal, 2000
We analyze a sample of 105 clusters having virial mass homogeneously estimated and for which gala... more 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. After suitable magnitude corrections and uniform conversions to B j band, we compute cluster luminosities L Bj within several clustercentric distances, 0.5, 1.0, 1.5 h −1 Mpc 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, which is the well-calibrated part of the COSMOS 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 Bj , and galaxy velocity dispersion, σ v , with L Bj ∝ σ 2.1-2.3 v. Our estimate of typical value for the mass-to-light ratio is M/L Bj ∼ 250 h M /L. We do not find any correlation of M/L Bj 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 ∝ L 1.2-1.3 Bj. We verify the robustness of this relation against a number of possible systematics. We verify that this increasing trend of M/L with cluster mass cannot be entirely due to a higher spiral fraction in poorer clusters, thus suggesting that a similar result would also be found by using R band galaxy magnitudes.
The Astrophysical Journal, 2002
We study the mass-to-light ratio of galaxy systems from poor groups to rich clusters, and present... more We study the mass-to-light ratio of galaxy systems from poor groups to rich clusters, and present for the first time a large database for useful comparisons with theoretical predictions. We extend a previous work, where B j band luminosities and optical virial masses were analyzed for a sample of 89 clusters. Here we also consider a sample of 52 more clusters, 36 poor clusters, 7 rich groups, and two catalogs, of ∼ 500 groups each, recently identified in the Nearby Optical Galaxy sample by using two different algorithms. We obtain the blue luminosity and virial mass for all systems considered. We devote a large effort to establishing the homogeneity of the resulting values, as well as to considering comparable physical regions, i.e. those included within the virial radius. By analyzing a fiducial, combined sample of 294 systems we find that the mass increases faster than the luminosity: the linear fit gives M ∝ L 1.34±0.03 B , with a tendency for a steeper increase in the low-mass range. In agreement with the previous work, our present results are superior owing to the much higher statistical significance and the wider dynamical range covered (∼ 10 12-10 15 M). We present a comparison between our results and the theoretical predictions on the relation between M/L B and halo mass, obtained by combining cosmological numerical simulations and semianalytic modeling of galaxy formation.
The Astrophysical Journal, 2001
We consider a sample of 51 distant galaxy clusters at 0.15 ∼ < z ∼ < 0.9 (< z >∼ 0.3), each clust... more We consider a sample of 51 distant galaxy clusters at 0.15 ∼ < z ∼ < 0.9 (< z >∼ 0.3), each cluster having at least 10 galaxies with available redshift in the literature. We select member galaxies, analyze the velocity dispersion profiles, and evaluate in a homogeneous way cluster velocity dispersions and virial masses. We apply the same procedures already recently applied on a sample of nearby clusters (z < 0.15, Girardi et al. 1998b) in order to properly analyze the possible dynamical evolution of galaxy clusters. We remark problems induced by the poor sampling and the small spatial extension of the sampled cluster region in the computation of velocity dispersion. We do not find any significant difference between nearby and distant clusters. In particular, we consider the galaxy spatial distribution, the shape of the velocity dispersion profile, and the relations between velocity dispersion and X-ray luminosity and temperature. Our results imply little dynamical evolution in the range of redshift spanned by our cluster sample, and suggest that the typical redshift of cluster formation is higher than that of the sample we analyze.
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Papers by marino mezzetti