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We study a sample of 883 sources detected in a deep Very Large Array survey at 1.4 GHz in the Extended Chandra Deep Field South. The paper focuses on the identification of their optical and infrared (IR) counterparts. We use a likelihood ratio technique that is particularly useful when dealing with deep optical images to minimize the number of spurious associations. We find a reliable counterpart for 95% of our radio sources. Most of the counterparts (74%) are detected at optical wavelengths, but there is a significant fraction (21%) only detectable in the IR. Combining newly acquired optical spectra with data from the literature we are able to assign a redshift to 81% of the identified radio sources (37% spectroscopic). We also investigate the X-ray properties of the radio sources using the Chandra 4 Ms and 250 ks observations. In particular, we use a stacking technique to derive the average properties of radio objects undetected in the Chandra images. The results of our analysis are collected in a new catalog containing the position of the optical/IR counterpart, the redshift information and the X-ray fluxes. It is the deepest multi-wavelength catalog of radio sources, which will be used for future study of this galaxy population., 18 pages, 11 figures, accepted for publication in ApJS, Table 3 and 5 are available in their entirety in the ancillary data

We study the spectral properties of the unresolved cosmic X-ray background (CXRB) in the 1.5-7.0 keV energy band with the aim of providing an observational constraint on the statistical properties of those sources that are too faint to be individually probed. We made use of the Swift X-ray observation of the Chandra Deep Field South complemented by the Chandra data. Exploiting the lowest instrument background (Swift) together with the deepest observation ever performed (Chandra) we measured the unresolved emission at the deepest level and with the best accuracy available today. We find that the unresolved CXRB emission can be modeled by a single power law with a very hard photon index Gamma=0.1+/-0.7 and a flux of 5(+/-3)E-12 cgs in the 2.0-10 keV energy band (1 sigma error). Thanks to the low instrument background of the Swift-XRT, we significantly improved the accuracy with respect to previous measurements. These results point towards a novel ingredient in AGN population synthesis models, namely a positive evolution of the Compton-thick AGN population from local Universe to high redshift., 11 pages 12 figures; A&A in press