IEAD: A Novel One-Line Interface to Query Astronomical Science Archives

In this article I present IEAD, a new interface for astronomical science databases. It is based on a powerful, yet simple, syntax designed to completely abstract the user from the structure of the underlying database. The programming language chosen for its implementation, JavaScript, makes it possible to interact directly with the user and to provide real-time information on the parsing process, error messages, and the name resolution of targets; additionally, the same parsing engine is used for context-sensitive autocompletion. Ultimately, this product should significantly simplify the use of astronomical archives, inspire more advanced uses of them, and allow the user to focus on what scientific research to perform, instead of on how to instruct the computer to do it.Comment: 13 pages, PASP in pres

Improving the accuracy of mass reconstructions from weak lensing: local shear measurements

Different options can be used in order to measure the shear from observations in the context of weak lensing. Here we introduce new methods where the isotropy assumption for the distribution of the source galaxies is implemented directly on the observed quadrupole moments. A quantitative analysis of the error associated with the finite number of source galaxies and with their ellipticity distribution is provided, applicable even when the shear is not weak. Monte Carlo simulations based on a realistic sample of source galaxies show that our procedure generally leads to errors ~30% smaller than those associated with the standard method of Kaiser and Squires (1993).Comment: 9 pages and 3 Postscript figures, uses A&A TeX macros. To be published in A&

Improving the accuracy of mass reconstructions from weak lensing: from the shear map to the mass distribution

In this paper we provide a statistical analysis of the parameter-free method often used in weak lensing mass reconstructions. It is found that a proper assessment of the errors involved in such a non-local analysis requires the study of the relevant two-point correlation functions. After calculating the two-point correlation function for the reduced shear, we determine the expected error on the inferred mass distribution and on other related quantities, such as the total mass, and derive the error power spectrum. This allows us to optimize the reconstruction method, with respect to the kernel used in the inversion procedure. In particular, we find that curl-free kernels are bound to lead to more accurate mass reconstructions. Our analytical results clarify the arguments and the numerical simulations by Seitz & Schneider (1996).Comment: 11 pages and 2 Postscript figures, uses A&A TeX macros. Submitted to A&A. Changed conten

A fast direct method of mass reconstruction for gravitational lenses

Statistical analyses of observed galaxy distortions are often used to reconstruct the mass distribution of an intervening cluster responsible for gravitational lensing. In current projects, distortions of thousands of source galaxies have to be handled efficiently; much larger data bases and more massive investigations are envisaged for new major observational initiatives. In this article we present an efficient mass reconstruction procedure, a direct method that solves a variational principle noted in an earlier paper, which, for rectangular fields, turns out to reduce the relevant execution time by a factor from 100 to 1000 with respect to the fastest methods currently used, so that for grid numbers N = 400 the required CPU time on a good workstation can be kept within the order of 1 second. The acquired speed also opens the way to some long-term projects based on simulated observations (addressing statistical or cosmological questions) that would be, at present, practically not viable for intrinsically slow reconstruction methods.Comment: 6 pages, 2 figures. Uses A&A macros. Accepted for pubblication on A&

Weak lensing and cosmology

Recently, it has been shown that it is possible to reconstruct the projected mass distribution of a cluster from weak lensing provided that both the geometry of the universe and the probability distribution of galaxy redshifts are known; actually, when additional photometric data are taken to be available, the galaxy redshift distribution could be determined jointly with the cluster mass from the weak lensing analysis. In this paper we develop, in the spirit of a ``thought experiment,'' a method to constrain the geometry of the universe from weak lensing, provided that the redshifts of the source galaxies are measured. The quantitative limits and merits of the method are discussed analytically and with a set of simulations, in relation to point estimation, interval estimation, and test of hypotheses for homogeneous Friedmann-Lemaitre models. The constraints turn out to be significant when a few thousand source galaxies are used.Comment: 17 pages, 8 figures. Uses A&A LaTeX style. Accepted for pubblication by A&A. Several changes made: new model for the lens; Sect. 7 and App. A. adde

Looking at the Fundamental Plane through a gravitational lens

We consider the Fundamental Plane of elliptical galaxies lensed by the gravitational field of a massive deflector (typically, a cluster of galaxies). We show that the Fundamental Plane relation provides a straightforward measurement of the projected mass distribution of the lens with a typical accuracy of ~0.15 in the dimensionless column density kappa. The proposed technique breaks the mass-sheet degeneracy completely and is thus expected to serve as an important complement to other lensing-based analyses. Moreover, its ability to measure directly the mass distribution on the small pencil beams that characterize the size of background galaxies may lead to crucial tests for current scenarios of structure formation.Comment: ApJL, in pres

On the origin of intrinsic alignment in cosmic shear measurements: an analytic argument

Galaxy intrinsic alignment can be a severe source of error in weak-lensing studies. The problem has been widely studied by numerical simulations and with heuristic models, but without a clear theoretical justification of its origin and amplitude. In particular, it is still unclear whether intrinsic alignment of galaxies is dominated by formation and accretion processes or by the effects of the instantaneous tidal field acting upon them. We investigate this question by developing a simple model of intrinsic alignment for elliptical galaxies, based on the instantaneous tidal field. Making use of the galaxy stellar distribution function, we estimate the intrinsic alignment signal and find that although it has the expected dependence on the tidal field, it is too weak to account for the observed signal. This is an indirect validation of the standard view that intrinsic alignment is caused by formation and/or accretion processes.Comment: 11 pages, 4 figures, accepted for publication on Astronomy & Astrophysic

The Cluster Experience In China

industrial clusters, China, local development

Indirect estimation of elliptical stable distributions

We present an indirect estimation approach for elliptical stable distributions which relies on the use of a multivariate t distribution as auxiliary model. This distribution is also elliptical and we show that its parameters have a one-to-one relationship with those of the elliptical stable, therefore making the proposed indirect approach especially suitable.Standard asymptotic properties are also shown and we analyze the finite sample behavior of the estimators via a comprehensive Monte Carlo study. An application to 27 emerging markets stock indexes concludes the paper.stable, elliptical, high dimension, multivariate, indirect inference