1,720,957 research outputs found
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
Recalibration of the <i>M</i> <sub>BH</sub> – <i>σ</i> <sub>⋆</sub> Relation for AGN
Full text linkWe present a recalibration of the M-BH-sigma(star) relation, based on a sample of 16 reverberation-mapped galaxies with newly determined bulge stellar velocity dispersions (sigma(star)) from integral-field spectroscopy (IFS), and a sample of 32 quiescent galaxies with publicly available IFS. For both samples, sigma(star) is determined via two different methods that are popular in the literature, and we provide fits for each sample based on both sets of sigma(star). We find the fit to the active galactic nucleus sample is shallower than the fit to the quiescent galaxy sample, and that the slopes for each sample are in agreement with previous investigations. However, the intercepts to the quiescent galaxy relations are notably higher than those found in previous studies, due to the systematically lower sigma(star) measurements that we obtain from IFS. We find that this may be driven, in part, by poorly constrained measurements of bulge effective radius (r(e)) for the quiescent galaxy sample, which may bias the sigma(star) measurements low. We use these quiescent galaxy parameterizations, as well as one from the literature, to recalculate the virial scaling factor f. We assess the potential biases in each measurement, and suggest f = 4.82 +/- 1.67 as the best currently available estimate. However, we caution that the details of how sigma(star) is measured can significantly affect f, and there is still much room for improvement.NSF through CAREER [AST-1253702]; Danish Council for Independent Research [DFF 4002-00275]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Dynamical Analysis of Three Candidate Bound Superclusters of Galaxies
No full textObservations of the Universe on the largest scales have revealed a breathtaking and vast filamentary structure, with dense superclusters of galaxies connected by lower density sheets and filaments, surrounding large voids that are almost completely devoid of luminous matter. The superclusters of galaxies, which are the largest structures in the Universe, are generally not sufficiently dense to be gravitationally bound, and they therefore expand with the Universe. However, in recent decades it has been suggested that there should exist a small number of superclusters with sufficient matter density to be gravitationally bound. To date only one such structure, the Shapley Supercluster, has ever been confirmed, but several other candidate bound superclusters have been identified.
I present a dynamical analysis of three candidate bound superclusters of galaxies; The Corona Borealis Supercluster (CSC), the Aquarius Supercluster (ASC), and the Microscopium Supercluster (MSC). Two galaxy scaling relations, the Fundamental Plane and the Kormendy Relation, are used to make redshift independent distance determinations to each of the clusters in the densest region of each supercluster. The inter-cluster dynamics are assessed by comparing these distances with spectroscopic redshifts. If the clusters are strongly interacting gravitationally, as will be the case if the supercluster is bound, then the redshift of each cluster will include both the recession velocity due to the expansion of the Universe, and the peculiar velocity due to the gravitational interactions. The peculiar velocity components are isolated in this study, and used to infer the current dynamical state of each supercluster. High quality data from the Sloan Digital Sky Survey are used for analysis of the CSC, and allow for an accurate assessment of the dynamics that clearly indicates extended bound structure. Extensive comparisons with simulations and analytical models convincingly demonstrate that the CSC is a bound supercluster. Data for both the MSC and ASC come from an observing program designed for the purpose, and are of sufficient quality to allow for a preliminary analysis of the dynamical state of each structure. These analyses indicate that both superclusters may be bound, and a more detailed analysis is warranted
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
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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