A Turn-over in the Galaxy Luminosity Function of the Coma Cluster Core?

Our previous study of the faint end (R$\leq$21.5) of the galaxy luminosity function (GLF) was based on spectroscopic data in a small region near the Coma cluster center. In this previous study Adami et al. (1998) suggested, with moderate statistical significance, that the number of galaxies actually belonging to the cluster was much smaller than expected. This led us to increase our spectroscopic sample. Here, we have improved the statistical significance of the results of the Coma GLF faint end study (R$\leq$22.5) by using a sample of 85 redshifts. This includes both new spectroscopic data and a literature compilation. The relatively small number of faint galaxies belonging to Coma that was suggested by Adami et al. (1998) and Secker et al. (1998) has been confirmed with these new observations. We also confirm that the color-magnitude relation is not well suited for finding the galaxies inside the Coma cluster core, close to the center at magnitudes fainter than R$\sim$19. We show that there is an enhancement in the Coma line of sight of field galaxies compared to classical field counts. This can be explained by the contribution of groups and of a distant $z\sim 0.5$ cluster along the line of sight. The result is that the Coma GLF appears to turn-over or at least to become flat for the faint galaxies. We suggest that this is due to environmental effects.Comment: 8 pages, 6 postscript figures, accepted in A&A, new table 1, updated figure

L-functions with large analytic rank and abelian varieties with large algebraic rank over function fields

The goal of this paper is to explain how a simple but apparently new fact of linear algebra together with the cohomological interpretation of L-functions allows one to produce many examples of L-functions over function fields vanishing to high order at the center point of their functional equation. The main application is that for every prime p and every integer g>0 there are absolutely simple abelian varieties of dimension g over Fp(t) for which the BSD conjecture holds and which have arbitrarily large rank.Comment: To appear in Inventiones Mathematica

The CFH Optical PDCS survey (COP) I: The Data

This paper presents and gives the COP (COP: CFHT Optical PDCS; CFHT: Canada-France-Hawaii Telescope; PDCS: Palomar Distant Cluster Survey) survey data. We describe our photometric and spectroscopic observations with the MOS multi-slit spectrograph at the CFH telescope. A comparison of the photometry from the PDCS (Postman et al. 1996) catalogs and from the new images we have obtained at the CFH telescope shows that the different magnitude systems can be cross-calibrated. After identification between the PDCS catalogues and our new images, we built catalogues with redshift, coordinates and V, I and Rmagnitudes. We have classified the galaxies along the lines of sight into field and structure galaxies using a gap technique (Katgert et al. 1996). In total we have observed 18 significant structures along the 10 lines of sight.Comment: 40 pages, 13 figures, accepted in A

Обеспечение безопасности радиоактивных источников на гипотетическом объекте

Объектом исследования является вопросы организации и функционирования систем физической защиты, учета и контроля ядерных материалов. Целью работы является создание методического подхода для описания и построения гипотетического объекта и его систем безопасности, с дальнейшем его применением в учебных целях по специальности Безопасность и нераспространение ядерных материалов.The object of research is the organization and functioning of systems of physical protection, accounting and control of nuclear materials. The aim of the work is to create a methodological approach to the description and construction of a hypothetical object and its security systems, with its further application for educational purposes in the specialty safety and non-proliferation of nuclear materials

An extension of the SHARC survey

We report on our search for distant clusters of galaxies based on optical and X-ray follow up observations of X-ray candidates from the SHARC survey. Based on the assumption that the absence of bright optical or radio counterparts to possibly extended X-ray sources could be distant clusters. We have obtained deep optical images and redshifts for several of these objects and analyzed archive XMM-Newton or Chandra data where applicable. In our list of candidate clusters, two are probably galaxy structures at redshifts of z$\sim$0.51 and 0.28. Seven other structures are possibly galaxy clusters between z$\sim$0.3 and 1. Three sources are identified with QSOs and are thus likely to be X-ray point sources, and six more also probably fall in this category. One X-ray source is spurious or variable. For 17 other sources, the data are too sparse at this time to put forward any hypothesis on their nature. We also serendipitously detected a cluster at z=0.53 and another galaxy concentration which is probably a structure with a redshift in the [0.15-0.6] range. We discuss these results within the context of future space missions to demonstrate the necessity of a wide field of view telescope optimized for the 0.5-2 keV range.Comment: Accepted in A&

Elliptic curves of large rank and small conductor

For r=6,7,...,11 we find an elliptic curve E/Q of rank at least r and the smallest conductor known, improving on the previous records by factors ranging from 1.0136 (for r=6) to over 100 (for r=10 and r=11). We describe our search methods, and tabulate, for each r=5,6,...,11, the five curves of lowest conductor, and (except for r=11) also the five of lowest absolute discriminant, that we found.Comment: 16 pages, including tables and one .eps figure; to appear in the Proceedings of ANTS-6 (June 2004, Burlington, VT). Revised somewhat after comments by J.Silverman on the previous draft, and again to get the correct page break

Spectroscopic Observations of Optically Selected Clusters of Galaxies from the Palomar Distant Cluster Survey

We have conducted a redshift survey of sixteen cluster candidates from the Palomar Distant Cluster Survey (PDCS) to determine both the density of PDCS clusters and the accuracy of the estimated redshifts presented in the PDCS catalog (Postman et. al. 1996). We find that the matched-filter redshift estimate presented in the PDCS has an error sigma_z = 0.06 in the redshift range 0.1 < z < 0.35 based on eight cluster candidates with three or more concordant galaxy redshifts. We measure the low redshift (0.1 < z < 0.35) space density of PDCS clusters to be 31.3^{+30.5}_{-17.1} * E-06 h^3 Mpc^-3 (68% confidence limits for a Poisson distribution) for Richness Class 1 systems. We find a tentative space density of 10.4^{+23.4}_{-8.4}* E-06 h^3 Mpc^-3 for Richness Class 2 clusters. These densities compare favorably with those found for the whole of the PDCS and support the finding that the space density of clusters in the PDCS is a factor of ~5 above that of clusters in the Abell catalog (Abell 1958; Abell, Corwin, and Olowin 1989). These new space density measurements were derived as independently as possible from the original PDCS analysis and therefore, demonstrate the robustness of the original work. Based on our survey, we conclude that the PDCS matched-filter algorithm is successful in detecting real clusters and in estimating their true redshifts in the redshift range we surveyed.Comment: 23 pages with 4 figures and 3 seperate tables. To be published in the November Issue of the Astronomical Journa

A new model of a tidally disrupted star

A new semi-analytical model of a star evolving in a tidal field is proposed. The model is a generalization of the so-called 'affine' stellar model. In our model the star is composed of elliptical shells with different parameters and different orientations, depending on time and on the radial Lagrangian coordinate of the shell. The evolution equations of this model are derived from the virial relations under certain assumptions, and the integrals of motion are identified. It is shown that the evolution equations can be deduced from a variational principle. The evolution equations are solved numerically and compared quantitatively with the results of 3D numerical computations of the tidal interaction of a star with a supermassive black hole. The comparison shows very good agreement between the main ``integral'' characteristics describing the tidal interaction event in our model and in the 3D computations. Our model is effectively a one-dimensional Lagrangian model from the point of view of numerical computations, and therefore it can be evolved numerically $10^{2}-10^{3}$ times faster than the 3D approach allows. This makes our model well suited for intensive calculations covering the whole parameter space of the problem.Comment: This version is accepted for publication in ApJ. Stylistic and grammatical changes, new Appendix adde

On the nature of faint Low Surface Brightness galaxies in the Coma cluster

This project is the continuation of our study of faint Low Surface Brightness Galaxies (fLSBs) in one of the densest nearby galaxy regions known, the Coma cluster. Our goal is to improve our understanding of the nature of these objects by comparing the broad band spectral energy distribution with population synthesis models. The data were obtained with the MEGACAM and CFH12K cameras at the CFHT. We used the resulting photometry in 5 broad band filters (u*, B, V, R, and I), that included new u*-band data, to fit spectral models. With these spectral fits we inferred a cluster membership criterium, as well as the ages, dust extinctions, and photometric types of these fLSBs. We show that about half of the Coma cluster fLSBs have a spectral energy distribution well represented in our template library while the other half present a flux deficit at ultraviolet wavelengths. Among the well represented, ~80% are probably part of the Coma cluster based on their spectral energy distribution. They are relatively young (younger than 2.3 Gyrs for 90% of the sample) non-starburst objects. The later their type, the younger fLSBs are. A significant part of the fLSBs are quite dusty objects. fLSBs are low stellar mass objects (the later their type the less massive they are), with stellar masses comparable to globular clusters for the faintest ones. Their characteristics are correlated with infall directions, confirming the disruptive origin for part of them.Comment: Accepted for publication in A&A, 10 pages, 10 figure