1,245 research outputs found
Testing the accuracy of reflection-based supermassive black hole spin measurements in AGN
X-ray reflection is a very powerful method to assess the spin of supermassive
black holes (SMBHs) in active galactic nuclei (AGN), yet this technique is not
universally accepted. Indeed, complex reprocessing (absorption, scattering) of
the intrinsic spectra along the line of sight can mimic the relativistic
effects on which the spin measure is based. In this work, we test the
reliability of SMBH spin measurements that can currently be achieved through
the simulations of high-quality XMM-Newton and NuSTAR spectra. Each member of
our group simulated ten spectra with multiple components that are typically
seen in AGN, such as warm and (partial-covering) neutral absorbers,
relativistic and distant reflection, and thermal emission. The resulting
spectra were blindly analysed by the other two members. Out of the 60 fits, 42
turn out to be physically accurate when compared to the input model. The SMBH
spin is retrieved with success in 31 cases, some of which (9) are even found
among formally inaccurate fits (although with looser constraints). We show
that, at the high signal-to-noise ratio assumed in our simulations, neither the
complexity of the multi-layer, partial-covering absorber nor the input value of
the spin are the major drivers of our results. The height of the X-ray source
(in a lamp-post geometry) instead plays a crucial role in recovering the spin.
In particular, a success rate of 16 out of 16 is found among the accurate fits
for a dimensionless spin parameter larger than 0.8 and a lamp-post height lower
than five gravitational radii.Comment: 20 pages, 9 figures, 4 tables. Accepted for publication in A&
An Examination of the Spectral Variability in NGC 1365 with Suzaku
We present jointly analyzed data from three deep Suzaku observations of NGC
1365. These high signal-to-noise spectra enable us to examine the nature of
this variable, obscured AGN in unprecedented detail on timescales ranging from
hours to years. We find that, in addition to the power-law continuum and
absorption from ionized gas seen in most AGN, inner disk reflection and
variable absorption from neutral gas within the Broad Emission Line Region are
both necessary components in all three observations. We confirm the clumpy
nature of the cold absorbing gas, though we note that occultations of the inner
disk and corona are much more pronounced in the high-flux state (2008) than in
the low-flux state (2010) of the source. The onset and duration of the "dips"
in the X-ray light curve in 2010 are both significantly longer than in 2008,
however, indicating that either the distance to the gas from the black hole is
larger, or that the nature of the gas has changed between epochs. We also note
significant variations in the power-law flux over timescales similar to the
cold absorber, both within and between the three observations. The warm
absorber does not vary significantly within observations, but does show
variations in column density of a factor of more than 10 on timescales less
than 2 weeks that seem unrelated to the changes in the continuum, reflection or
cold absorber. By assuming a uniform iron abundance for the reflection and
absorption, we have also established that an iron abundance of roughly 3.5
times the solar value is sufficient to model the broad-band spectrum without
invoking an additional partial-covering absorber. Such a measurement is
consistent with previous published constraints from the 2008 Suzaku observation
alone, and with results from other Seyfert AGN in the literature.Comment: 19 pages, 11 figures, accepted for publication in MNRA
The circumnuclear environment of IRAS 20551-4250 a case study of AGN/Starburst connection for JWST
We present a general review of the current knowledge of IRAS 20551-4250 and
its circumnuclear environment. This Ultraluminous Infrared Galaxy is one of the
most puzzling sources of its class in the nearby Universe: the near-IR spectrum
is typical of a galaxy experiencing a very intense starburst, but a highly
obscured active nucleus is identified beyond 5 micron and possibly dominates
the mid-IR energy output of the system. At longer wavelengths star formation is
again the main driver of the global spectral shape and features. We interpret
all the available IR diagnostics in the framework of simultaneous black hole
growth and star formation, and discuss the key properties that make this source
an ideal laboratory for the forthcoming James Webb Space Telescope.Comment: 19 pages, 7 figures, 2 tables. Accepted for pubblication in Advances
in Astronomy. To appear in the special issue: "Seeking for the Leading Actor
on the Cosmic Stage: Galaxies versus Supermassive Black Holes
Analysis of Spitzer-IRS spectra of hyperluminous infrared galaxies
Hyperluminous infrared galaxies (HLIRG) are the most luminous persistent
objects in the Universe. They exhibit extremely high star formation rates, and
most of them seem to harbour an AGN. They are unique laboratories to
investigate the most extreme star formation, and its connection to
super-massive black hole growth. The AGN and SB relative contributions to the
total output in these objects is still debated. Our aim is to disentangle the
AGN and SB emission of a sample of thirteen HLIRG. We have studied the MIR low
resolution spectra of a sample of thirteen HLIRG obtained with the IRS on board
Spitzer. The 5-8 {\mu}m range is an optimal window to detect AGN activity even
in a heavily obscured environment. We performed a SB/AGN decomposition of the
continuum using templates, successfully applied for ULIRG in previous works.
The MIR spectra of all sources is largely dominated by AGN emission. Converting
the 6 {\mu}m luminosity into IR luminosity, we found that ~80% of the sample
shows an IR output dominated by the AGN emission. However, the SB activity is
significant in all sources (mean SB contribution ~30%), showing star formation
rates ~300-3000 solar masses per year. Using X-ray and MIR data we estimated
the dust covering factor (CF) of these HLIRG, finding that a significant
fraction presents a CF consistent with unity. Along with the high X-ray
absorption shown by these sources, this suggests that large amounts of dust and
gas enshroud the nucleus of these HLIRG, as also observed in ULIRG. Our results
are in agreement with previous studies of the IR SED of HLIRG using radiative
transfer models, and we find strong evidence that all HLIRG harbour an AGN.
This work provides further support to the idea that AGN and SB are both crucial
to understand the properties of HLIRG. Our study of the CF supports the
hypothesis that HLIRG can be divided in two different populations.Comment: 17 pages, 9 figures, 4 tables. Accepted for publication in A&
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
Gravitational Backreaction Effects on the Holographic Phase Transition
We study radion stabilization in the compact Randall-Sundrum model by
introducing a bulk scalar field, as in the Goldberger and Wise mechanism, but
(partially) taking into account the backreactions from the scalar field on the
metric. Our generalization reconciles the radion potential found by Goldberger
and Wise with the radion mass obtained with the so-called superpotential method
where backreaction is fully considered. Moreover we study the holographic phase
transition and its gravitational wave signals in this model. The improved
control over backreactions opens up a large region in parameter space and
leads, compared to former analysis, to weaker constraints on the rank N of the
dual gauge theory. We conclude that, in the regime where the 1/N expansion is
justified, the gravitational wave signal is detectable by LISA.Comment: 42 pages, 4 figures; v2: minor changes for the publicatio
Classical Nucleation Theory for Active Fluid Phase Separation
Classical nucleation theory (CNT), linking rare nucleation events to the free
energy landscape of a growing nucleus, is central to understanding phase-change
kinetics in passive fluids. Nucleation in non-equilibrium systems is much
harder to describe because there is no free energy, but instead a
dynamics-dependent quasi-potential that typically must be found numerically.
Here we extend CNT to a class of active phase separating systems governed by a
minimal field-theoretic model (Active Model B+). In the small noise and
supersaturation limits that CNT assumes, we compute analytically the
quasi-potential, and hence nucleation barrier, for liquid-vapor phase
separation. Crucially to our results, detailed balance, although broken
microscopically by activity, is restored along the instanton trajectory, which
in CNT involves the nuclear radius as the sole reaction coordinate
Clinical significance of epithelial-to-mesenchymal transition in laryngeal carcinoma: Its role in the different subsites
Background: During epithelial-to-mesenchymal transition, cancer cells lose adhesion capacity gaining migratory properties. The role of the process on prognosis has been evaluated in 50 cases of laryngeal carcinoma. Methods: E-cadherin, N-cadherin, β-catenin, α-catenin, γ-catenin, caveolin-1, and vimentin immunohistochemical expression were evaluated using a double score based on staining intensity and cellular localization. Results: Cytoplasmic E-cadherin and α/γ catenin staining were associated with a decrease in survival, cytoplasmic β-catenin was associated with advanced stage, and N-cadherin and vimentin expression were associated with poor differentiation and tumor relapse. On the basis of cancer cells, epithelial or mesenchymal morphological and immunophenotypic similarity we identified 4 main subgroups correlated with a transition to a more undifferentiated phenotype, which have a different pattern of relapse and survival. Conclusion: The negative prognostic role of epithelial-to-mesenchymal transition has been confirmed and a predictive role in glottic tumors has been suggested, leading us to propose epithelial-to-mesenchymal transition as an additional adverse feature in laryngeal carcinoma
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