18 research outputs found

    The Asiago-ESO/RASS QSO Survey. III. Clustering analysis and its theoretical interpretation

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    This is the third paper of a series describing the Asiago-ESO/RASS QSO survey (AERQS), a project aimed at the construction of an all-sky statistically well-defined sample of relatively bright QSOs (B<15) at z<0.3. We present here the clustering analysis of the full spectroscopically identified database (392 AGN). The clustering signal at 0.02<z<0.22 is detected at a 3-4 sigma level and its amplitude is measured to be r_0=8.6\pm 2.0 h^{-1} Mpc (in a LambdaCDM model). The comparison with other classes of objects shows that low-redshift QSOs are clustered in a similar way to Radio Galaxies, EROs and early-type galaxies in general, although with a marginally smaller amplitude. The comparison with recent results from the 2QZ shows that the correlation function of QSOs is constant in redshift or marginally increasing toward low redshift. We discuss this behavior with physically motivated models, deriving interesting constraints on the typical mass of the dark matter halos hosting QSOs, M_DMH= 10^{12.7} h^{-1} M_sun (10^{12.0}-10^{13.5}h^{-1} M_sun at 1 sigma confidence level). Finally, we use the clustering data to infer the physical properties of local AGN, obtaining M_BH=2 10^8 h^{-1} M_sun (10^7-3 10^9 h^{-1} M_sun) for the mass of the active black holes, tau_{AGN}= 8 10^6 yr (2 10^{6}-5 10^{7} yr) for their life-time and eta = 0.14 for their efficiency (always for a LambdaCDM model).Comment: 37 pages, Astronomical Journal in press. Changes to match the referee comment

    Asymptomatic primary infection with Epstein-Barr virus: observations on young adult cases

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    Epstein-Barr virus (EBV) is typically acquired asymptomatically in childhood. By contrast, infection later in life often leads to infectious mononucleosis (IM), a febrile illness characterised by anti-EBV IgM antibody-positivity, high loads of circulating latently-infected B cells, and a marked lymphocytosis caused by hyper-expansion of EBV-specific CD8+ T cells plus milder expansion of CD56dim NKG2A+ KIR– NK cells. How the two situations compare is unclear due to the paucity of studies on clinically-silent infection. Here we describe five prospectively-studied asymptomatic infections identified in a sero-epidemiological survey of University entrants. In each case the key blood sample had high cell-associated viral loads without marked IM-like CD8 lymphocytosis or NK cell disturbance. Two of the highest viral load cases showed a coincident expansion of activated EBV-specific CD8+ T cells but overall CD8+ T cell numbers were either unaffected or only mildly increased. Two slightly lower load cases, which serology suggests may have been caught earlier in the course of infection, also showed no T or NK cell expansion at the time. Interestingly, in another higher load case where T and NK cell responses were undetectable in the primary infection bleed, EBV-specific T cell responses did not appear until several months later, by which time virus loads in the blood had already fallen. Thus some asymptomatic primary infections have very high circulating viral loads and a cell-mediated immune response that is qualitatively similar to IM but of lower magnitude. However, others may be quite different and ultimately could reveal novel mechanisms of host control

    Detecting the Highest Redshift (z > 8) QSOs in a Wide, Near Infrared Slitless Spectroscopic Survey

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    We investigate the prospects of extending observations of high redshift QSOs to z>8 by means of a very wide-area near-infrared slitless spectroscopic survey, e.g. the planned survey with the European Space Agency's Euclid telescope. For any QSOs at z>8.06 the strong Lyman-alpha line will enter the wavelength range of the Euclid near-infrared spectrometer and imaging photometer (NISP). We perform a detailed simulation of Euclid NISP slitless spectroscopy (with the parameters of the wide survey) in an artificial field containing QSO spectra at all redshifts up to z=12. The simulation spectra are analysed with an automated redshift finder, and a detection rate estimated as a function of H magnitude and redshift. Spectroscopic identification of QSOs would reach deeper limits for the redshift ranges where either H-alpha (0.678.06) is visible. Furthermore, if photometrically-selected z>8 spectra can be re-examined and re-fitted to minimize the effects of spectral contamination, the QSO detection rate in the Lyman-alpha window will be increased by an estimated 60% and will then be better here than at any other redshift, with an effective limit H=21.5. With an extrapolated rate of QSO evolution, we predict the Euclid wide (15000 sq. deg.) spectroscopic survey will identify 20-35 (19-33 with a small correction for lineless objects) very luminous QSOs at z>8.06.Comment: 16 pages, 19 figures, accepted for publication in MNRA

    4MOST : the 4-metre multi-object spectroscopic telescope project in the assembly, integration, and test phase

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    4MOST is a new high-multiplex, wide-field spectroscopic survey facility under construction for ESO's 4m-VISTA telescope at Paranal, Chile. Its key specifications are: a large field of view of 4.4 square degrees, a high multiplex fibre positioner based on the tilting spine principle that positions 2436 science fibres in the focal surface of which 1624 fibres go to two low-resolution optical spectrographs (R = λ/Δλ ~ 6500) and 812 fibres transfer light to the high-resolution optical spectrograph (R ~ 20,000). Currently, almost all subsystems are completed and full testing in Europe will be finished in spring 2023, after which 4MOST will be shipped to Chile. An overview is given of instrument construction and capabilities, the planned science of the consortium and the recently selected community programmes, and the unique operational scheme of 4MOST
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