1,721,110 research outputs found
An increase in black hole activity in galaxies with kinematically misaligned gas
No full textExternal accretion events such as a galaxy merger or the accretion of gas from the immediate environment of a galaxy can create a large misalignment between the gas and the stellar kinematics. Numerical simulations have suggested that misaligned structures may promote the inflow of gas to the nucleus of the galaxy and the accretion of gas by the central supermassive black hole. We show for the first time that galaxies with a strong misalignment between the ionized gas and stellar kinematic angles have a higher observed fraction of active black holes than galaxies with aligned rotation of gas and stars. The increase in black hole activity suggests that the process of formation and/or the presence of misaligned structures are connected with the fuelling of active supermassive black holes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Flares in the changing look AGN Mrk 590 – II. Deep X-ray observations reveal a Comptonizing inner accretion flow
No full textMrk 590 is a changing look active galactic nucleus (AGN) currently in an unusual repeat X-ray and UV flaring state. Here, we report on deep X-ray observations with XMM–Newton, NuSTAR, and NICER, obtained at a range of X-ray flux levels. We detect a prominent soft excess below 2 keV; its flux is tightly correlated with that of both the X-ray and UV continuum, and it persists at the lowest flux levels captured. Our Bayesian model comparison strongly favours inverse Comptonization as the origin of this soft excess, instead of blurred reflection. We find only weak reflection features, with R ≲ 0.4 assuming Compton-thick reflection. Most of this reprocessing occurs at least ∼800 gravitational radii (roughly three light-days) from the continuum source. Relativistically broadened emission is weak or absent, suggesting the lack of a standard ‘thin disc’ at small radii. We confirm that the predicted broad-band emission due to Comptonization is roughly consistent with the observed UV–optical photometry. This implies an optically thick, warm (kTe ∼ 0.3 keV) scattering region that extends to at least ∼ 103 gravitational radii, reprocessing any UV thermal emission. The lack of a standard ‘thin disc’ may also explain the puzzling ∼ 3-d X-ray to UV delay previously measured for Mrk 590. Overall, we find that the X-ray spectral changes in Mrk 590 are minimal, despite substantial luminosity changes. Other well-studied changing look AGN display more dramatic spectral evolution, e.g. disappearing continuum or soft excess. This suggests that a diversity of physical mechanisms in the inner accretion flow may produce a UV–optical changing-look event.</p
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Improving calibration of the MBH-σ* relation for AGN with the BRAVE program
No full textThe MBH - σ* relation for AGN, which relates
the mass of the central supermassive black hole (MBH) to the
bulge stellar velocity dispersion (σ*) of the host
galaxy, is a powerful tool for studying the evolution of structure
across cosmic time. Accurate calibration of this relation is essential,
and much effort has been put into improving MBH
determinations with this in mind. However calibration remains difficult
because many nearby AGN with secure MBH determinations are
hosted by late-type galaxies, with significant kinematic substructure
such as bars, disks and rings. Kinematic substructure is known to
contaminate and bias σ* determinations from long-slit
and single aperture spectroscopy, ultimately limiting the utility of the
MBH - σ* relation, and hampering efforts to
investigate morphological dependencies. Integral-field spectroscopy
(IFS) can be used to map the two dimensional kinematics, providing a
method for measuring σ* absent some of the biases
inherent in other methods, and giving a more complete picture of the
spatial variations in the dynamics. We present the first set of results
from the BRAVE program, the long-term goal of which is to use IFS to
more accurately determine σ* for the calibrating sample
of reverberation-mapped AGN. We present IFS kinematic maps for the
sample of galaxies we have so far observed, which show clearly how
spatial variation can impact σ* determinations from
long-slit spectroscopy. We present a new fit to the MBH -
σ* relation for the sample of 16 reverberation-mapped
AGN for which we currently have σ* determinations from
IFS, as well as a new determination of the virial scaling factor, f, for
use with reverberation-mapping
Flares in the changing look AGN Mrk 590. I: The UV response to X-ray outbursts suggests a more complex reprocessing geometry than a standard disk
No full textMrk 590 is a known changing-look AGN which almost turned off in 2012, and then in 2017 partially re-ignited into a repeat flaring state, unusual for an AGN. Our \emph{Swift} observations since 2013 allow us to characterise the accretion-generated emission and its reprocessing in the central engine of a changing-look AGN. The X-ray and UV variability amplitudes are higher than those typically observed in `steady-state' AGN at similar moderate accretion rates; instead, the variability is similar to that of highly accreting AGN. The unusually strong X-ray to UV correlation suggests that the UV-emitting region is directly illuminated by X-ray outbursts. We find evidence that the X-rays are reprocessed by two UV components, with the dominant one at 3 days and a faint additional reprocessor at near-zero lag. However, we exclude a significant contribution from diffuse broad line region continuum, known to contribute for bona-fide AGN. A near-zero lag is expected for a standard `lamp-post' disk reprocessing model with a driving continuum source near the black hole. That the overall UV response is dominated by the 3-day lagged component suggests a complicated reprocessing geometry, with most of the UV continuum not produced in a compact disk, as also found in recent studies of NGC 5548 and NGC 4151. Nonetheless, the observed flares display characteristic timescales of 100 rest-frame days, consistent with the expected thermal timescale in an accretion disk
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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