A recent revision of black hole scaling relations indicate that the local mass density in black holes should be five times higher than previously determined values. The local black hole mass density ...is connected to the mean radiative efficiency of accretion through the time integral of the Active Galactic Nuclei (AGN) volume density and a significant increase in the local black hole mass density would have interesting consequences on AGN accretion properties and demography. One possibility to explain a large black hole mass density is that most of the black hole growth is via radiatively inefficient channels such as super Eddington accretion; however, this solution is not unique. Here we show how it is possible to accommodate a larger fraction of heavily buried, Compton-thick AGNs, without violating the limit imposed by the spectral energy density of the hard X-ray and mid–infrared backgrounds.
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Context. The Milagro hot spot A, close to the Galactic anticenter direction, has been tentatively attributed to cosmic rays from a local reservoir (at a distance ≈100 pc), freely streaming along ...diverging and smooth magnetic field lines. This is at variance with the geometry of the ≈kpc scale Galactic magnetic field, which is known to be aligned with the spiral arms. Aims. We investigate the information available on the geometry of the magnetic field on the scales (≈100 pc) of relevance here. Methods. The magnetic field immediately upstream of the heliosphere has been investigated by previous authors by modeling the interaction of this field with the solar wind. At larger distances, we use the dispersion measure and the rotation measure of nearby pulsars (especially towards the third Galactic quadrant). Additional information about the local field towards the North Polar Spur is taken from previous studies of the diffuse radio emission and the polarization of starlight. Results. The asymmetry of the heliosphere with respect to the incoming interstellar medium implies a magnetic field almost orthogonal to the local spiral arm, in the general direction of hot spot A, but more to the south. This is in good agreement with the nearby pulsar data on the one side, and the North Polar Spur data on the other. Conclusions. The local magnetic field on scales of ≈100 parsecs around the Sun seems to be oriented so as to provide a direct connection between the Solar System and a possible site of the Geminga supernova; the residual angular difference and the shape and orientation of the Milagro hot spot can be attributed to the field trailing in the wake of the heliosphere.
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We present the results of a 5–8 μm spectral analysis performed on the largest sample of local ultraluminous infrared galaxies (ULIRGs) selected so far, consisting of 164 objects up to a redshift of ...∼0.35. The unprecedented sensitivity of the Infrared Spectrograph onboard Spitzer allowed us to develop an effective diagnostic method to quantify the active galactic nucleus (AGN) and starburst (SB) contribution to this class of objects. The large AGN over SB brightness ratio at 5–8 μm and the sharp difference between the spectral properties of AGN and SB galaxies in this wavelength range make it possible to detect even faint or obscured nuclear activity, and disentangle its emission from that of star formation. By defining a simple model we are also able to estimate the intrinsic bolometric corrections for both the AGN and SB components, and obtain the relative AGN/SB contribution to the total luminosity of each source. Our main results are the following. The AGN detection rate among local ULIRGs amounts up to 70 per cent, with 113/164 convincing detections within our sample, while the global AGN/SB power balance is ∼1/3. A general agreement is found with optical classification; however, among the objects with no spectral signatures of nuclear activity, our IR diagnostics find a subclass of elusive, highly obscured AGN. We analyse the correlation between nuclear activity and IR luminosity, recovering the well-known trend of growing AGN significance as a function of the overall energy output of the system: the sources exclusively powered by star formation are mainly found at LIR < 1012.3 L⊙, while the average AGN contribution rises from ∼10 to ∼60 per cent across the ULIRG luminosity range. From a morphological point of view, we confirm that the AGN content is larger in compact systems, but the link between activity and evolutionary stage is rather loose. By analysing a control sample of IR-luminous galaxies around z∼ 1, we find evidence for only minor changes with redshift of the large-scale spectral properties of the AGN and SB components. This underlines the potential of our method as a straightforward and quantitative AGN/SB diagnostic tool for ULIRG-like systems at high redshift as well, and hints to possible photometric variants for fainter sources.
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Recent time-resolved spectral studies of a few active galactic nuclei (AGNs) in hard X-rays revealed occultations of the X-ray primary source probably by broad-line region (BLR) clouds. An important ...open question on the structure of the circumnuclear medium of AGN is whether this phenomenon is common, i.e. whether a significant fraction of the X-ray absorption in AGN is due to BLR clouds. Here, we present the first attempt to perform this kind of analysis in a homogeneous way, on a statistically representative sample of AGN, consisting of the ∼40 brightest sources with long XMM–Newton and/or Suzaku observations. We describe our method, based on a simple analysis of hardness-ratio light curves, and its validation through a complete spectroscopic analysis of a few cases. We find that X-ray eclipses, most probably due to clouds at the distance of the BLR, are common in sources where the expected occultation time is compatible with the observation time, while they are not found in sources with longer estimated occultation times. Overall, our results show that occultations by BLR clouds may be responsible for most of the observed X-ray spectral variability at energies higher than 2 keV, on time-scales longer than a few ks.
The blood-brain barrier is a highly selective anatomical and functional interface allowing a unique environment for neuro-glia networks. Blood-brain barrier dysfunction is common in most brain ...disorders and is associated with disease course and delayed complications. However, the mechanisms underlying blood-brain barrier opening are poorly understood. Here we demonstrate the role of the neurotransmitter glutamate in modulating early barrier permeability in vivo Using intravital microscopy, we show that recurrent seizures and the associated excessive glutamate release lead to increased vascular permeability in the rat cerebral cortex, through activation of NMDA receptors. NMDA receptor antagonists reduce barrier permeability in the peri-ischemic brain, whereas neuronal activation using high-intensity magnetic stimulation increases barrier permeability and facilitates drug delivery. Finally, we conducted a double-blind clinical trial in patients with malignant glial tumors, using contrast-enhanced magnetic resonance imaging to quantitatively assess blood-brain barrier permeability. We demonstrate the safety of stimulation that efficiently increased blood-brain barrier permeability in 10 of 15 patients with malignant glial tumors. We suggest a novel mechanism for the bidirectional modulation of brain vascular permeability toward increased drug delivery and prevention of delayed complications in brain disorders.
In this study, we reveal a new mechanism that governs blood-brain barrier (BBB) function in the rat cerebral cortex, and, by using the discovered mechanism, we demonstrate bidirectional control over brain endothelial permeability. Obviously, the clinical potential of manipulating BBB permeability for neuroprotection and drug delivery is immense, as we show in preclinical and proof-of-concept clinical studies. This study addresses an unmet need to induce transient BBB opening for drug delivery in patients with malignant brain tumors and effectively facilitate BBB closure in neurological disorders.
AMAZE Maiolino, R.; Nagao, T.; Grazian, A. ...
Astronomy and astrophysics (Berlin),
09/2008, Volume:
488, Issue:
2
Journal Article
Peer reviewed
We present initial results of an ESO-VLT large programme (AMAZE) aimed at determining the evolution of the mass-metallicity relation at z > 3 by means of deep near-IR spectroscopy. Gas metallicities ...are measured, for an initial sample of nine star forming galaxies at z similar to 3.5, by means of optical nebular lines redshifted into the near-IR. Stellar masses are accurately determined by using Spitzer-IRAC data, which sample the rest-frame near-IR stellar light in these distant galaxies. When compared with previous surveys, the mass-metallicity relation inferred at z similar to 3.5 shows an evolution much stronger than observed at lower redshifts. The evolution is prominent even in massive galaxies, indicating that z similar to 3 is an epoch of major action in terms of star formation and metal enrichment also for massive systems. There are also indications that the metallicity evolution of low mass galaxies is stronger relative to high mass systems, an effect which can be considered the chemical version of the galaxy downsizing. The mass- metallicity relation observed at z similar to 3.5 is difficult to reconcile with the predictions of some hierarchical evolutionary models. Such discrepancies suggest that at z > 3 galaxies are assembled mostly with relatively un-evolved sub-units, i.e. small galaxies with low star formation efficiency. The bulk of the star formation and metallicity evolution probably occurs once small galaxies are already assembled into bigger systems.
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We present the first results of a project, Lyman-break galaxies Stellar populations and Dynamics (LSD), aimed at obtaining spatially resolved, near-infrared (IR) spectroscopy of a complete sample of ...Lyman-break galaxies at z∼ 3. Deep observations with adaptive optics resulted in the detection of the main optical lines, such as O iiλ3727, Hβ and O iiiλ5007, which are used to study sizes, star formation rates (SFRs), morphologies, gas-phase metallicities, gas fractions and effective yields. Optical, near-IR and Spitzer/Infrared Array Camera photometry are used to measure stellar mass. We obtain that morphologies are usually complex, with the presence of several peaks of emissions and companions that are not detected in broad-band images. Typical metallicities are 10–50 per cent solar, with a strong evolution of the mass–metallicity relation from lower redshifts. Stellar masses, gas fraction and evolutionary stages vary significantly among the galaxies, with less massive galaxies showing larger fractions of gas. In contrast with observations in the local universe, effective yields decrease with stellar mass and reach solar values at the low-mass end of the sample. This effect can be reproduced by gas infall with rates of the order of the SFRs. Outflows are present but are not needed to explain the mass–metallicity relation. We conclude that a large fraction of these galaxies is actively creating stars after major episodes of gas infall or merging.
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