3,554 research outputs found

    Luminosity Functions beyond the spectroscopic limit. I. Method and near-infrared LFs in the HDF-N and HDF-S

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    We have developed a Monte Carlo method to compute the luminosity function of galaxies, based on photometric redshifts, which takes into account the non-gaussianity of the probability functions, and the presence of degenerate solutions in redshift. In this paper we describe the method and the mock tests performed to check its reliability. The NIR luminosity functions and the redshift distributions are determined for near infrared subsamples on the HDF-N and HDF-S. The results on the evolution of the NIR LF, the stellar mass function, and the luminosity density, are presented and discussed in view of the implications for the galaxy formation models. The main results are the lack of substantial evolution of the bright end of the NIR LF and the absence of decline of the luminosity density up to a redshift z ~ 2, implying that most of the stellar population in massive galaxies was already in place at such redshift.Comment: 23 pages, 19 figures. Accepted for publication in A&A. No change

    Keck Deep Fields. I. Observations, Reductions, and the Selection of Faint Star-Forming Galaxies at Redshifts z~4, 3, and 2

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    We introduce a very deep, R_lim~27, multicolor imaging survey of very faint star-forming galaxies at z~4, z~3, z~2.2, and z~1.7. This survey, carried out on the Keck I telescope, uses the very same UGRI filter system that is employed by the Steidel team to select galaxies at these redshifts, and thus allows us to construct identically-selected, but much fainter, samples. However, our survey reaches ~1.5 mag deeper than the work of Steidel and his group, letting us probe substantially below the characteristic luminosity L* and thus study the properties and redshift evolution of the faint component of the high-z galaxy population. The survey covers 169 square arcminutes in three spatially independent patches on the sky and -- to R<~27 -- contains 427 GRI-selected z~4 LBGs, 1481 UGR-selected z~3 LBGs, 2417 UGR-selected z~2.2 star-forming galaxies, and 2043 UGR-selected z~1.7 star-forming galaxies. In this paper, the first in a series, we introduce the survey, describe our observing and data reduction strategies, and outline the selection of our z~4, z~3, z~2.2, and z~1.7 samples.Comment: To appear in Ap

    Binary interactions and UV photometry on photometric redshift

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    Using the Hyperz code (Bolzonella et al. 2000) we present photometric redshift estimates for a random sample of galaxies selected from the SDSS/DR7 and GALEX/DR4, for which spectroscopic redshifts are also available. We confirm that the inclusion of ultraviolet photometry improves the accuracy of photo-zs for those galaxies with g*-r* < 0.7 and z_spec < 0.2. We also address the problem of how binary interactions can affect photo-z estimates, and find that their effect is negligible.Comment: 2 pages 1 figure

    Photometric Redshifts for an Optical/Near-Infrared Catalogue in the Chandra Deep Field South

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    Photometric redshifts have proven a powerful tool in identifying galaxies over a large range of lookback times. We have been generalising this technique to incorporate the selection of candidate high redshift QSOs. We have applied this to a large optical/near-infrared imaging survey in 6 wavebands aiming to push farther in redshift (and fainter in luminosity) than previous studies. We believe that study of these very faint and distant objects provides valuable insights into galaxy formation and evolution. Here we present work in progress and preliminary results for a catalogue of objects detected as part of the Las Campanas Infrared Survey. This is a stepping stone to the type of survey data that will become available in the next few years from projects such as UKIDSS and VISTA.Comment: 4 pages LaTeX, submitted to the "Eurokiel 2002: Galaxy Evolution III: From Simple Models to Self Consistant Approaches" Conference Proceeding

    Tracking the impact of environment on the galaxy stellar mass function up to z ~ 1 in the 10 k zCOSMOS sample

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    We study the impact of the environment on the evolution of galaxies in the zCOSMOS 10 k sample in the redshift range 0.1 ≀ z ≀ 1.0 over an area of ~1.5 deg^2. The considered sample of secure spectroscopic redshifts contains about 8500 galaxies, with their stellar masses estimated by SED fitting of the multiwavelength optical to near-infrared (NIR) photometry. The evolution of the galaxy stellar mass function (GSMF) in high and low density regions provides a tool to study the mass assembly evolution in different environments; moreover, the contributions to the GSMF from different galaxy types, as defined by their SEDs and their morphologies, can be quantified. At redshift z ~ 1, the GSMF is only slightly dependent on environment, but at lower redshifts the shapes of the GSMFs in high- and low-density environments become extremely different, with high density regions exhibiting a marked bimodality, not reproducible by a single Schechter function. As a result of this analysis, we infer that galaxy evolution depends on both the stellar mass and the environment, the latter setting the probability of a galaxy to have a given mass: all the galaxy properties related to the stellar mass show a dependence on environment, reflecting the difference observed in the mass functions. The shapes of the GSMFs of early- and late-type galaxies are almost identical for the extremes of the density contrast we consider, ranging from isolated galaxies to rich group members. The evolution toward z = 0 of the transition mass M_(cross), i.e., the mass at which the early- and late-type GSMFs match each other, is more rapid in high density environments, because of a difference in the evolution of the normalisation of GSMFs compared to the total one in the considered environment. The same result is found by studying the relative contributions of different galaxy types, implying that there is a more rapid evolution in overdense regions, in particular for intermediate stellar masses. The rate of evolution is different for sets of galaxy types divided on the basis of their SEDs or their morphologies, tentatively suggesting that the migration from the blue cloud to the red sequence occurs on a shorter timescale than the transformation from disc-like morphologies to ellipticals. Our analysis suggests that environmental mechanisms of galaxy transformation start to be more effective at z < 1. The comparison of the observed GSMFs to the same quantities derived from a set of mock catalogues based on semi-analytical models shows disagreement, in both low and high density environments: in particular, blue galaxies in sparse environments are overproduced in the semi-analytical models at intermediate and high masses, because of a deficit of star formation suppression, while at z < 0.5 an excess of red galaxies is present in dense environments at intermediate and low masses, because of the overquenching of satellites

    An experimental setup for the detection of e+e- pairs in the decay of 8Be*

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    The existence of a light neutral boson, possible mediator of a new fundamental interaction, has been recently proposed by A.J. Krasznahorkay and collaborators. A series of experiments was carried out at the Atomki laboratory (Debrecen,Hungary) measuring electron-positron pairs emitted in the decay of excited 8Be and 4He. Anomalies in the e+e− angular correlation distributions with respect to the Internal Pair Creation (IPC) process have been reported. The first results concern the decay of the 18.15 MeV 1+ state in 8Be, while the group later focused on the ≈20 MeV excited states in 4He. In order to explain the reported anomaly several interpretation have been developed. The approach proposed by X. Zhang and G. Miller aims to describe the anomalies in an almost conventional nuclear physics framework, improving the reaction modeling. Conversely, a possible interpretation given by J. Feng and collaborators involves the appearance of a new gauge vector boson, called X17, that could possibly mediate the interaction between the SM and the dark sector. The Atomki results and the related interpretations triggered a renewed interest in the spectroscopy of light ions by Internal Pair Creation. At this purpose, a new experimental setup is being developed at the INFN Legnaro National Laboratories of INFN (Legnaro, Padova, Italy). The first goal is to provide an independent replica of the Hungarian experiment. This thesis work focuses on a complete simulation of the proposed setup and reports about the first experimental characterization of the prototype detectors. The text is organized as follows: after a short introduction on the physics of electromagnetic transitions and internal pair production in nuclei, the state of the art regarding the 8Be and the 4He anomalies will be discussed, explaining the roots of the X-boson or X17 case. Afterwards, the simulation and the experimental characterization works will be reported

    Aperçu de la méthanisation agricole en Italie

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    La mise en place et le dĂ©veloppement de la mĂ©thanisation sont intrinsĂšquement liĂ©s Ă  des questions gĂ©ographiques et aux prises de position des institutions. Il est intĂ©ressant d’observer comment cela s’opĂšre en Italie, de voir oĂč les prioritĂ©s sont placĂ©es et quels choix sont fait, notamment ici dans la rĂ©gion de VĂ©nĂ©tie

    A Test of Photometric Redshifts for X-ray Selected Sources

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    We test the effectiveness of photometric redshifts based upon galaxy spectral template fitting for X-ray luminous objects, using a sample of 65 sources detected by Chandra in the field of the Caltech Faint Galaxy Redshift Survey (CFGRS). We find that sources with quasar-dominated spectra (for which galaxy spectral templates are not appropriate) are easily identified, and that photometric redshifts are robust for the rest of the sources in our sample. Specifically, for the 59 sources that are not quasar-dominated at optical wavelengths, we find that the photometric redshift estimates have scatter comparable to the field galaxy population in this region. There is no evidence for a trend of increasing dispersion with X-ray luminosity over the range L_X = 10^39 - 5x10^43 erg/s, nor is there a trend with the ratio of X-ray to optical flux, f_X/f_R. The practical implication of this work is that photometric redshifts should be robust for the majority (~90%) of the X-ray sources down to f_X ~ 10^-16 erg/s/cm^2 that have optical counterparts brighter than R ~ 24. Furthermore, the same photometry can be easily used to identify the sources for which the photometric redshifts are likely to fail. Photometric redshift estimation can thus be utilized as an efficient tool in analyzing the statistical properties of upcoming large Chandra and XMM-Newton data sets and identifying interesting subsamples for further study.Comment: To appear in ApJ (6 pages, 6 figures). Replaced with accepted versio

    Benefits and Drawbacks of Non-Destructive Assay (NDA) for Nuclear Safeguards – An Overview

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    Nuclear safeguards are technical measures used to detect the diversion of nuclear material and technologies from their peaceful use. A key trait of safeguards is represented by measurements, which allow operators and inspectors to verify the nuclear activities and the amount of nuclear material declared by the States. In particular, an important class of measurements are Non-Destructive Assay (NDA) techniques, which allow one to characterize samples while preserving their physical integrity. NDA represents a rapid and effective method for measurements of nuclear materials in a variety of situations (from process lines to finished products, scrap and waste materials), with the possibility to perform on-site measurements, reducing radioactive waste production and offering wide margins for automatization and remote operation. However, there are situations where the use of NDA is not recommended or possible and one has to rely on Destructive Assay (DA) (i.e., techniques which alter the integrity of the item analysed). This happens, for example, in environmental sampling, when dealing with highly diluted nuclear materials, or when the radiation emitted by the sample is weakly penetrating. In conclusion, the integrated use of different NDA and DA techniques is the best possible solution for measurements in the frame of nuclear safeguards