1,721,163 research outputs found
Cosmological simulations of black hole growth: AGN luminosities and downsizing
No full textIn this study, we present a detailed, statistical analysis of black hole growth and the evolution of active galactic nuclei (AGN) using cosmological hydrodynamic simulations run down to z = 0. The simulations self-consistently follow radiative cooling, star formation, metal enrichment, black hole growth and associated feedback processes from both Type II/Ia supernovae and AGN. We consider two simulation runs, one with a large comoving volume of (500 Mpc)3 and one with a smaller volume of (68 Mpc)3 but with a factor of almost 20 higher mass resolution. We compare the predicted statistical properties of AGN with results from large observational surveys. Consistently with previous results, our simulations can widely match observed black hole properties of the local Universe. Furthermore, our simulations can successfully reproduce the evolution of the bolometric AGN luminosity function for both the low-luminosity and the high-luminosity end up to z = 3.0, only at z = 1.5-2.5, the low-luminosity end is overestimated by up to 1 dex. In addition, the smaller but higher resolution run is able to match the observational data of the low bolometric luminosity end at higher redshifts z = 3-4. We also perform a direct comparison with the observed soft and hard X-ray luminosity functions of AGN, including an empirical correction for a torus-level obscuration, and find a similarly good agreement. These results nicely demonstrate that the observed `antihierarchical' trend in the AGN number density evolution (i.e. the number densities of luminous AGN peak at higher redshifts than those of faint AGN) is self-consistently predicted by our simulations. Implications of this downsizing behaviour on active black holes, their masses and Eddington ratios are discussed. Overall, the downsizing behaviour in the AGN number density as a function of redshift can be mainly attributed to the evolution of the gas density in the resolved vicinity of a (massive) black hole (which is depleted with evolving time as a consequence of star formation and AGN feedback)
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
From points to galaxies: learning from IFS surveys of nearby galaxies
No full textI will present results on the spatially resolved stellar population (SP) properties of nearby galaxies, obtained by joining integral field spectroscopy from CALIFA and broad-band images in a Bayesian framework with a highly complex SP modelling. These results highlight the role of local scales in determining the physical properties of SPs, resulting in local scaling relations linking age and metallicity with stellar mass surface density (Zibetti et al. 2017, 2019). The spatial variations of SP parameters provide invaluable insights into the formation and evolution of early-type galaxies: our original results (Zibetti et al. 2019) suggest a two-phase scenario as the most plausible one. I will also show that not only spatial resolution enhances the diagnostic power of spectral/SED fitting techniques, but also the mutual links between the physical properties of different regions of galaxies in structural and kinematical continuity allow us to refine our spectral/SED fitting techniques.</p
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
Signatures of AGN feedback in synthetic nebular emission lines of simulated, massive galaxies
No full textWe present a detailed analysis of the effect of AGN feedback on integrated and spatially resolved synthetic optical emission lines for simulated massive galaxies at different cosmic epochs. The theoretical emission lines are derived from coupling "new-generation" nebular models, accounting for photo-ionisation due to young stars, AGN and post-AGB stellar populations, to new sets of cosmological zoom-in simulations of massive galaxies, run with and without AGN feedback. Investigating the evolution of BPT diagrams, we demonstrate that AGN feedback is crucial to reproduce the observed decrease in [OIII]/Hb from high to low redshift, via regulating the SF in massive galaxies. We additionally highlight the multifaceted imprint of AGN feedback on projected 2D emission line maps, such as (i) central Ha deficiencies and reduced extent of Ha emission, (ii) flattened [NII]/Ha gradients, and (iii) extended low ionisation emission — overall, more consistent with recent observations. Finally, prospects will be given, to what extent our novel interface between simulations and observations will contribute to the interpretation of up-coming high-z, high-quality spectroscopic data, e.g. from JWST
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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