Together with accretion and evolution, orientation is one of the three main drivers in the grand unification of active galactic nuclei (AGNs). Being unresolved, determining the true inclination of ...those powerful sources is always difficult and indirect, yet it remains a vital clue to apprehend the numerous, panchromatic and complex spectroscopic features we detect. There have only been 100 inclinations derived so far; in this context, can we be sure that we measure the true orientation of AGNs? To answer this question, four methods to estimate the nuclear inclination of AGNs are investigated and compared to inclination-dependent observables (hydrogen column density, Balmer linewidth, optical polarization and flux ratios within the infrared and relative to X-rays). Among these orientation indicators, the method developed by Fisher, Crenshaw, Kraemer, and others, mapping and modelling the radial velocities of the O iii emission region in AGNs, is the most successful. The O iii-mapping technique shows highly statistically significant correlations at >95 per cent confidence level for rejecting the null hypothesis for all the test cases. Such results confirm that the unified model is correct at a scale ranging from kiloparsec to a fraction of a parsec. However, at a radial distance less than 0.01 pc from the central black hole, warps and misalignments may change this picture.
A handful of active galactic nuclei (AGN) have shown strong spectral variations in the optical band between epochs that are years apart. The appearance or disappearance of broad emission lines in ...their spectra completely changes their classification. Since their nucleus orientation cannot change on such short timescales, another physical interpretation has to be found. Several scenarios have been offered to explain their changing-look nature, and for the first time, we conduct polarized radiative transfer Monte Carlo simulations for all the models. We demonstrate that all interpretations have distinctive features in both total optical flux and continuum polarization, such as suggested by pioneering previous observations. Distinguishing between the different scenarios is thus straightforward. We apply our results on the changing-look quasar J1011+5442 and confirm the conclusions found previously: in this specific case, the disappearance of the broad emission lines is due to a change in accretion rate.
The anisotropic nature of active galactic nuclei (AGN) is thought to be responsible for the observational differences between type-1 (pole-on) and type-2 (edge-on) nearby Seyfert-like galaxies. In ...this picture, the detection of emission and/or absorption features is directly correlated to the inclination of the system. The AGN structure can be further probed by using the geometry-sensitive technique of polarimetry, yet the pairing between observed polarization and Seyfert type remains poorly examined. Based on archival data, I report here the first compilation of 53 estimated AGN inclinations matched with ultraviolet/optical continuum polarization measurements. Corrections, based on the polarization of broad emission lines, are applied to the sample of Seyfert-2 AGN to remove dilution by starburst light and derive information about the scattered continuum alone. The resulting compendium agrees with past empirical results, i.e. type-1 AGN show low polarization degrees (P ≤ 1 per cent) predominantly associated with a polarization position angle parallel to the projected radio axis of the system, while type-2 objects show stronger polarization percentages (P > 7 per cent) with perpendicular polarization angles. The transition between type-1 and type-2 inclination occurs between 45° and 60° without noticeable impact on P. The compendium is further used as a test to investigate the relevance of four AGN models. While an AGN model with fragmented regions matches observations better than uniform models, a structure with a failed dusty wind along the equator and disc-born, ionized, polar outflows is by far closer to observations. However, although the models correctly reproduce the observed dichotomy between parallel and perpendicular polarization, as well as correct polarization percentages at type-2 inclinations, further work is needed to account for some highly polarized type-1 AGN.
We create the first broad-band polarization spectrum of an active galactic nucleus (AGN) by compiling the 0.1–100 $$\mu$$m, 4.9, and 15 GHz continuum polarization of NGC 1068 from more than 50 yr of ...observations. Despite the diversity of instruments and apertures, the observed spectrum of linear continuum polarization has distinctive wavelength-dependent signatures that can be related to the AGN and host galaxy physics. The impact of the Big Blue bump and infrared bump, together with electron, Mie scattering, dichroism, and synchrotron emission are naturally highlighted in polarization, allowing us to reveal the type-1 AGN core inside this type-2 object with unprecedented precision. In order to isolate the AGN component, we reconstruct the spectral energy distribution of NGC 1068 and estimate the fraction of diluting light in the observed continuum flux. This allows us to clearly and independently show that, in the case of NGC 1068, Thomson scattering is the dominant mechanism for the polarization in the optical band. We also investigate the effect of aperture on the observed polarization and confirm previous findings on the extension of the narrow line region of NGC 1068 and on the B-band and K-band polarization from the host. Finally, we do not detect statistically significant aperture-corrected polarimetric variations over the last 52 yr, suggesting that the parsec-scale morphological and magnetic geometries probably remained stable for more than half a century.
Context. One of the main challenges for polarimetric observations of active galactic nuclei (AGN) is to properly estimate the amount of parasitic light that contaminates the polarization signal. ...Removing this unpolarized flux is a complex task that has only been achieved in a couple of objects. Aims. In this fifth paper of the series, we present a new version of the Monte Carlo code STOKES that accounts for dilution by interstellar polarization and host starlight in radiative transfer modeling. Methods. We upgraded our code by including spectral energy distribution (SED) templates for a set of representative host galaxies. The unpolarized light emitted by those hosts alters the observer polarization while being coherently radiatively coupled to the AGN structure. We also included in our analysis tool a routine that may add, depending on the user’s objectives, an interstellar component. Results. Using a generic AGN model, we illustrate how interstellar polarization and starlight dilution impact the observed polarimetric signal of AGN. We applied our code to NGC 1068, an archetypal edge-on AGN and demonstrate that STOKES can reproduce its SED, the expected wavelength-dependent polarimetric signatures, and the observed high-angular resolution polarimetric maps. Using the flexibility of the code, we derived several intrinsic parameters such as the system inclination and the torus opening angle. Conclusions. The new version of our publicly available code now allows observers to better prepare their observations, interpret their data and simulate the three-dimensional geometry and physics of AGN in order to probe unresolved structures. Additionally, the radiative interaction between the host and the AGN can be used to probe the co-evolution of the system.
Emerging fungal diseases can drive amphibian species to local extinction. During 2010-2016, we examined 1,921 urodeles in 3 European countries. Presence of the chytrid fungus Batrachochytrium ...salamandrivorans at new locations and in urodeles of different species expands the known geographic and host range of the fungus and underpins its imminent threat to biodiversity.
Several clinical trials have produced conflicting results regarding the benefit of antioxidants in cancer therapy thus questioning the incorporation of these substances in standard treatment ...regimens. Vitamins E and C, selenium, carotenoids, lycopene, soy products, and green tea extract are a few substances with antioxidant properties that have been studied in detail. This article reviews the results generated over the last 20 years through in vitro and in vivo studies in various types of cancers and stages of cancer treatment. Despite the commercial popularity and the multitude of studies examining antioxidant therapy, the true role of antioxidants is yet to be determined, requiring further investigation into its propagative, causal, or protective nature.
Context. The innermost regions in active galactic nuclei (AGNs) have not yet been spatially resolved, but spectropolarimetry can provide insight into their hidden physics and geometry. From ...spectropolarimetric observations in broad emission lines and assuming equatorial scattering as a dominant polarization mechanism, it is possible to estimate the mass of supermassive black holes (SMBHs) residing at the center of AGNs. Aims. We explore the possibilities and limits, and put constraints on the method for determining SMBH masses using polarization in broad emission lines by providing more in-depth theoretical modeling. Methods. We used the Monte Carlo radiative transfer code STOKES to explore polarization properties of Type-1 AGNs. We modeled equatorial scattering using flared-disk geometry for a set of different SMBH masses assuming Thomson scattering. In addition to the Keplerian motion, which is assumed to be dominant in the broad-line region (BLR), we also considered cases of additional radial inflows and vertical outflows. Results. We modeled the profiles of polarization plane position angle φ, degree of polarization, and total unpolarized lines for different BLR geometries and different SMBH masses. Our model confirms that the method can be widely used for Type-1 AGNs when viewing inclinations are between 25° and 45°. We show that the distance between the BLR and scattering region (SR) has a significant impact on the mass estimates and the best mass estimates are when the SR is situated at a distance 1.5–2.5 times larger than the outer BLR radius. Conclusions. Our models show that if Keplerian motion can be traced through the polarized line profile, then the direct estimation of the mass of the SMBH can be performed. When radial inflows or vertical outflows are present in the BLR, this method can still be applied if velocities of the inflow/outflow are less than 500 km s−1. We also find that models for NGC 4051, NGC 4151, 3C 273, and PG0844+349 are in good agreement with observations.
ABSTRACT We present a series of numerical models suitable for X-ray polarimetry of accreting systems. First, we provide a spectropolarimetric routine that integrates reflection from inner optically ...thick walls of a geometrical torus of arbitrary size viewed under general inclination. In the studied example, the equatorial torus is illuminated by a central isotropic source of X-ray power-law emission, representing a hot corona. Nearly neutral reprocessing inside the walls is precomputed by Monte Carlo code stokes that incorporates both line and continuum processes, including multiple scatterings and absorption. We created a new xspec model, called xsstokes, which in this version enables efficient X-ray polarimetric fitting of the torus parameters, observer’s inclination and primary emission properties, interpolating for arbitrary state of primary polarization. Comparison of the results to a Monte Carlo simulation allowing partial transparency shows that the no-transparency condition may induce different polarization by tens of per cent. Allowing partial transparency leads to lower/higher polarization fraction, if the resulting polarization orientation is perpendicular/parallel to the rotation axis. We provide another version of xsstokes that is suitable for approximating nearly neutral reflection from a distant optically thick disc of small geometrical thickness. It assumes local illumination averaged for a selected range of incident angles, representing a toy model of a diffuse corona of various physical extent. Assessing both xsstokes variants, we conclude that the resulting polarization can be tens of per cent and perpendicularly/parallelly oriented towards the rotation axis, if the reflecting medium is rather vertically/equatorially distributed with respect to a compact central source.
With a levitodynamics experiment in the strong and coherent quantum optomechanical coupling regime, we demonstrate that the oscillator acts as a broadband quantum spectrum analyzer. The asymmetry ...between positive and negative frequency branches in the displacement spectrum traces out the spectral features of the quantum fluctuations in the cavity field, which are thus explored over a wide spectral range. Moreover, in our two-dimensional mechanical system the quantum backaction, generated by such vacuum fluctuations, is strongly suppressed in a narrow spectral region due to a destructive interference in the overall susceptibility.
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