Towards an informed quest for accretion disc winds in quasars: the intriguing case of Ton 28

We report on the detection of a blueshifted Fe K absorption feature in two consecutive XMM–Newton  observations of the luminous blue quasar Ton 28, at the 4σ cumulative significance. The rest energy of 9.2 keV implies the presence of an accretion disc wind with bulk outflow velocity of ∼0.28c, while the kinetic power is most likely a few per cent of the quasar luminosity. Remarkably, Ton 28 had been specifically selected as an optimal target to reveal an ultra-fast X-ray wind based on its total luminosity (Lbol > 1046 erg s−1) and [O III] λ5007 Å equivalent width (EW < 6 Å), suggestive of high accretion rate and low inclination, respectively. Other peculiar optical/UV emission-line properties include narrow Hβ, strong Fe II, and blueshifted C IV . These are key parameters in the Eigenvector 1 formalism, and are frequently found in active galaxies with ongoing accretion disc winds, hinting at a common physical explanation. Provided that the effectiveness of our selection method is confirmed with similar sources, this result could represent the first step towards the characterization of black hole winds through multiwavelength indicators in the absence of high-quality X-ray spectra

Is there any evidence that ionised outflows quench star formation in type 1 quasars at z<1?

The aim of this paper is to test the basic model of negative AGN feedback. According to this model, once the central black hole accretes at the Eddington limit and reaches a certain critical mass, AGN driven outflows blow out gas, suppressing star formation in the host galaxy and self-regulating black hole growth. We consider a sample of 224 quasars selected from the SDSS at z<1 observed in the infrared band by Herschel. We evaluate the star formation rate in relation to several outflow signatures traced by the [OIII]4959,5007 and [OII]3726,3729 emission lines in about half of the sample with high quality spectra. Most of the quasars show asymmetric and broad wings in [OIII], which we interpret as outflow signatures. We separate the quasars in two groups, ``weakly'' and ``strongly'' outflowing, using three different criteria. When we compare the mean star formation rate in five redshift bins in the two groups, we find that the SFRs are comparable or slightly larger in the strongly outflowing quasars. We estimate the stellar mass from SED fitting and the quasars are distributed along the star formation main sequence, although with a large scatter. The scatter from this relation is uncorrelated with respect to the kinematic properties of the outflow. Moreover, for quasars dominated in the infrared by starburst or by AGN emission, we do not find any correlation between the star formation rate and the velocity of the outflow, a trend previously reported in the literature for pure starburst galaxies. We conclude that the basic AGN negative feedback scenario seems not to agree with our results. Although we use a large sample of quasars, we did not find any evidence that the star formation rate is suppressed in the presence of AGN driven outflows on large scale. A possibility is that feedback is effective over much longer timescales than those of single episodes of quasar activity.Comment: 18 pages, new version that implements the suggestions of the referee and matches the AA published versio

Quasars as standard candles II

A tight non-linear relation between the X-ray and the optical-ultraviolet (UV) emission has been observed in active galactic nuclei (AGN) over a wide range of redshift and several orders of magnitude in luminosity, suggesting the existence of an ubiquitous physical mechanism regulating the energy transfer between the accretion disc and the X-ray emitting corona. Recently, our group developed a method to use this relation in observational cosmology, turning quasars into standardizable candles. This work mainly seeks to investigate the potential evolution of this correction at high redshifts. We thus studied the LX − LUV relation for a sample of quasars in the redshift range 4 <  z <  7, adopting the selection criteria proposed in our previous work regarding their spectral properties. The resulting sample consists of 53 type 1 (unobscured) quasars, observed either with Chandra or XMM-Newton, for which we performed a full spectral analysis, determining the rest-frame 2 keV flux density, as well as more general X-ray properties such as the estimate of photon index, and the soft (0.5–2 keV) and hard (2–10 keV) unabsorbed luminosities. We find that the relation shows no evidence for evolution with redshift. The intrinsic dispersion of the LX–LUV for a sample free of systematics/contaminants is of the order of 0.22 dex, which is consistent with previous estimates from our group on quasars at lower redshift

Demography of obscured and unobscured AGN: prospects for a Wide Field X-ray Telescope

We discuss some of the main open issues in the evolution of Active Galactic Nuclei which can be solved by the sensitive, wide area surveys to be performed by the proposed Wide Field X-ray Telescope mission.Comment: Proceedings of "The Wide Field X-ray Telescope Workshop", held in Bologna, Italy, Nov. 25-26 2009. To appear in Memorie della Societa' Astronomica Italiana 2010 (arXiv:1010.5889

Human Herpesvirus 6 (HHV-6) Causes Severe Thymocyte Depletion in SCID-hu Thy/Liv Mice

Human herpesvirus 6 (HHV-6) is a potentially immunosuppressive agent that may act as a cofactor in the progression of AIDS. Here, we describe the first small animal model of HHV-6 infection. HHV-6 subgroup A, strain GS, efficiently infected the human thymic tissue implanted in SCID-hu Thy/Liv mice, leading to the destruction of the graft. Viral DNA was detected in Thy/Liv implants by quantitative polymerase chain reaction (PCR) as early as 4 d after inoculation and peaked at day 14. The productive nature of the infection was confirmed by electron microscopy and immunohistochemical staining. Atypical thymocytes with prominent nuclear inclusions were detected by histopathology. HHV-6 replication was associated with severe, progressive thymocyte depletion involving all major cellular subsets. However, intrathymic T progenitor cells (ITTPs) appeared to be more severely depleted than the other subpopulations, and a preferred tropism of HHV-6 for ITTPs was demonstrated by quantitative PCR on purified thymocyte subsets. These findings suggest that thymocyte depletion by HHV-6 may be due to infection and destruction of these immature T cell precursors. Similar results were obtained with strain PL-1, a primary isolate belonging to subgroup B. The severity of the lesions observed in this animal model underscores the possibility that HHV-6 may indeed be immunosuppressive in humans

Updating quasar bolometric luminosity corrections. II. Infrared bolometric corrections

We present infrared bolometric luminosity corrections derived from the detailed spectral energy distributions of 62 bright quasars of low- to moderate-redshift (z=0.03-1.4). At 1.5, 2, 3, 7, 12, 15, and 24 microns we provide bolometric corrections of the mathematical forms L_iso=\zeta \lambda L_\lambda and log(L_iso)=A+B log(\lambda L_\lambda). Bolometric corrections for radio-loud and radio-quiet objects are consistent within 95% confidence intervals, so we do not separate them. Bolometric luminosities estimated using these corrections are typically smaller than those derived from some commonly used in the literature. We investigate the possibility of a luminosity dependent bolometric correction and find that, while the data are consistent with such a correction, the dispersion is too large and the luminosity range too small to warrant such a detailed interpretation. Bolometric corrections at 1.5 $\mu$m are appropriate for objects with properties that fall in the range log(L_bol)=45.4-47.3 and bolometric corrections at all other wavelengths are appropriate for objects with properties that fall in the range log(L_bol)=45.1-47.0.Comment: 13 pages, 4 tables, 8 figures, accepted to MNRA

Centri ecclesiastici e dinamiche di popolamento: la fondazione dei borghi nuovi subalpini e l’eredità romanica

Le testimonianze di architettura dell’XI e del XII secolo costituiscono non solo documenti utili allo studio della cultura artistica e tecnica, ma sono indicatori significativi per lo studio della storia delle dinamiche insediative. Il processo di patrimonializzazione delle architetture romaniche ha seguito infatti percorsi strettamente legati alle sorti del popolamento nelle aree loro circostanti: nei casi in cui i villaggi si siano riallocati o ri-concentrati nel basso medioevo, si è verificato il fenomeno della ‘ruralizzazione’ delle architetture romaniche, associato a una sostanziale conservazione ‘fossile’ della loro facies originaria; ove invece l’insediamento abbia avuto fortuna demica e politica presso la chiesa, l’edificio medievale è stato conservato in maniera parziale o selettiva, subendo ordinariamente interventi di adeguamento liturgico e di gusto. Il fenomeno è stato studiato attraverso alcuni casi-studio relativi al dinamismo insediativo della fondazione di borghi nuovi tra XII e XIV secolo. The architectural examples dating to 11th and 12th centuries are not only important to studying artistic and technical culture, but they are also meaningful indicators about history of settlement dynamics. In fact, the process of patrimonialization of Romanesque architectures followed ways closely linked to the destiny of the population in the nearby areas. When villages were re-positioned or re-focused during the late Middle Ages, Romanesque architectures experienced phenomenon of ‘ruralisation’, in association with a significant conservation of their original appearance as a ‘fossil’. Instead, when settlements had demographic and political successful outcomes beside the church, the medieval buildings have been partially or selectively preserved, routinely undergoing interventions of liturgical and style adaptation. The phenomenon is studied through case studies related to the dynamism of the foundation of new villages between 12th and 14th centuries