The Asiago-ESO/RASS QSO Survey II. The Southern Sample

This is the second paper of a series describing the Asiago-ESO/RASS QSO survey, a project aimed at the construction of an all-sky statistically well-defined sample of very bright QSOs (B_J < 15). Such a survey is required to remove the present uncertainties about the properties of the local QSO population and constitutes an homogeneous database for detailed evolutionary studies of AGN. We present here the complete Southern Sample, which comprises 243 bright (12.60 < B_J < 15.13) QSO candidates at high galactic latitudes (|b_{gal}| > 30^{\circ}). The area covered by the survey is 5660 sq. deg. Spectroscopy for the 137 still unidentified objects has been obtained. The total number of AGN turns out to be 111, 63 of which are new identifications. The properties of the selection are discussed. The completeness and the success rate for this survey at the final stage are 63% and 46%, respectively.Comment: 36 pages Latex, with 15 PostScript figures. Accepted for publication in Astronomical Journa

Clustering at high redshift

The addition of deep near infrared images to the database provided by the HDF-S WFPC2 is essential to monitor the SEDs of the objects on a wide baseline and address a number of key issues including the total stellar content of baryonic mass, the effects of dust extinction, the dependence of morphology on the rest frame wavelength, the photometric redshifts, the detection and nature of extremely red objects (EROs). For these reasons deep near infrared images were obtained with the ISAAC instrument at the ESO VLT in the Js, H and Ks bands reaching, respectively, 23.5, 22.0, 22.0 limiting Vega-magnitude. A multi-color (F300, F450, F606, F814, Js, H, Ks) photometric catalog of the HDF-S has been produced. Photometric redshifts have been generated both fitting templates to the observed SEDs and with neural network techniques. Spectroscopic observations of the 9 candidates with I_AB <24.25 have confirmed all of them to be galaxies with 2<z<3.5. The photometric redshifts for all the galaxies brighter than I_AB< 27.5 have been used to study the evolution of galaxy clustering in the interval 0<z<4.5.Comment: 2 pages Latex, To appear in the proceedings of "The mass of galaxies at low and high redshift", Venice, Oct 24-26, 2001,eds. R. Bender and A. Renzini (ESO Astrophysics Symposia, Springer-Verlag

Dynamics and phase evolution of Bose-Einstein condensates in one-dimensional optical lattices

We report experimental results on the dynamics and phase evolution of Bose-Einstein condensates in 1D optical lattices. The dynamical behaviour is studied by adiabatically loading the condensate into the lattice and subsequently switching off the magnetic trap. In this case, the condensate is free to expand inside the periodic structure of the optical lattice. The phase evolution of the condensate, on the other hand, can be studied by non-adiabatically switching on the periodic potential. We observe decays and revivals of the interference pattern after a time-of-flight.Comment: 6 pages, 5 figures; submitted to the Proceedings of the 11th Laser Physics Workshop, Bratislava 200

Existence and approximation of probability measure solutions to models of collective behaviors

In this paper we consider first order differential models of collective behaviors of groups of agents based on the mass conservation equation. Models are formulated taking the spatial distribution of the agents as the main unknown, expressed in terms of a probability measure evolving in time. We develop an existence and approximation theory of the solutions to such models and we show that some recently proposed models of crowd and swarm dynamics fit our theoretic paradigm.Comment: 31 pages, 1 figur

A Low Upper Limit to the Lyman Continuum Emission of two galaxies at z 3

Long exposure, long-slit spectra have been obtained in the UV/optical bands for two galaxies at z=2.96 and z=3.32 to investigate the fraction of ionizing UV photons escaping from high redshifts galaxies. The two targets are among the brightest galaxies discovered by Steidel and collaborators and they have different properties in terms of Lyman-alpha emission and dust reddening. No significant Lyman continuum emission has been detected. The noise level in the spectra implies an upper limit of f_{rel,esc}\equiv 3 f(900)/f(1500)< 16% for the relative escape fraction of ionizing photons, after correction for absorption by the intervening intergalactic medium. This upper limit is 4 times lower than the previous detection derived from a composite spectrum of 29 Lyman break galaxies at z 3.4. If this value is typical of the escape fraction of the z 3 galaxies, and is added to the expected contribution of the QSO population, the derived UV background is in good agreement with the one derived by the proximity effect.Comment: 16 pages, 2 figures, ApJ Letters in pres