1,721,140 research outputs found
A Population of Intermediate-mass Black Holes in Dwarf Starburst Galaxies Up to Redshift=1.5
Full text linkWe study a sample of ∼50,000 dwarf starburst and late-type galaxies drawn from the COSMOS survey with the aim of investigating the presence of nuclear accreting black holes (BHs) as those seed BHs from which supermassive BHs could grow in the early universe. We divide the sample into five complete redshift bins up to z = 1.5 and perform an X-ray stacking analysis using the Chandra COSMOS-Legacy survey data. After removing the contribution from X-ray binaries and hot gas to the stacked X-ray emission, we still find an X-ray excess in the five redshift bins that can be explained by nuclear accreting BHs. This X-ray excess is more significant for z\lt 0.5. At higher redshifts, these active galactic nuclei could suffer mild obscuration, as indicated by the analysis of their hardness ratios. The average nuclear X-ray luminosities in the soft band are in the range 1039-1040 erg s-1. Assuming that the sources accrete at ≥1% the Eddington rate, their BH masses would be ≤105 {M}☉ , thus in the intermediate-mass BH regime, but their mass would be smaller than the one predicted by the BH-stellar mass relation. If instead the sources follow the correlation between BH mass and stellar mass, they would have sub-Eddington accreting rates of ∼10-3 and BH masses 1-9 × 105 {M}☉ . We thus conclude that a population of intermediate-mass BHs exists in dwarf starburst galaxies, at least up to z = 1.5, though their detection beyond the local universe is challenging due to their low luminosity and mild obscuration unless deep surveys are employed
HARD X-RAY-EMISSION FROM EXTRAGALACTIC IRAS 12-MICRON SOURCES - CONSTRAINTS ON THE UNIFIED ACTIVE GALACTIC NUCLEUS MODEL AND THE SYNTHESIS OF THE X-RAY-BACKGROUND
No full textWe analyze the 2-10 keV X-ray emission of recently compiled complete samples of active galactic nuclei (AGNs) and galaxies selected at 12 mu m. The content in active galaxies of the 12 mu m sample is indeed much larger and less biased against low-luminosity and ''hidden'' active nuclei than samples selected at other wavelengths. As a necessary complement, we also study the IR emissivity of the largest sample of hard-X-ray-selected AGNs. Our purposes are to probe the unified scheme of active nuclei and to evaluate the local X-ray volume emissivity of low-luminosity and ''hidden'' AGNs. Two methods are used in our analysis to search for X-ray emission in the HEAO I A-2 all-sky maps from the extragalactic sources contained in the extended 12 mu m sample: an X-ray intensity distribution analysis around the known positions of the sources and a cross-correlation function analysis between galaxy densities and X-ray intensities in the high Galactic latitude sky (\b\ > 25 degrees), where the catalog is more than 98% complete. The joint analysis of the X-ray-selected and 12 mu m-selected samples enables us to define the relationship between the X-ray and the mid-IR emissions of Seyfert nuclei. In particular, we find congruence between the hard X-ray and mid-IR Seyfert 1 nuclear-luminosity functions when a nonlinear relation L(12 mu m) proportional to L(5 keV)(0.8) is with appropriate dispersion, Although this result is easily explained by circumnuclear reradiation as the main source of the mid-IR emission, it nonetheless argues against the simplest version of the unified model for active nuclei. We confirm that X-ray emission is basically restricted to AGNs, finding Seyfert 1's to be much more powerful emitters than Seyfert 2's. We find no signal of X-ray emission for the remaining galaxies selected at 12 mu m, not even for those having a flat far-IR spectrum, which are prime candidates to host hidden AGNs. Our result on the local volume emissivity of the Seyfert 1's is fully consistent with those that we derive from studies of the hard X-ray luminosity function, The 95% upper limits to the local emissivity that we derive for the Seyfert 2 class and for the most likely ''hidden'' AGN candidates are consistent with models of the X-ray background recently proposed based on the unified Seyfert scheme. We also find that less than similar to 20% of Seyfert 1-like AGNs and less than similar to 50% of Seyfert 2-like AGNs can be ''hidden'' in the non-Seyfert-galaxy samples, assuming that the X-ray-to-12 mu m flux ratios measured in the 12 mu m-selected samples can be considered typical for these classes of objects. In this case, the number ratio of Seyfert 2 to Seyfert 1 galaxies ranges from 1 to 2
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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