1,721,207 research outputs found
Feedback from quasars in star-forming galaxies and the triggering of massive galactic winds
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The effect of stellar feedback and quasar winds on the active galactic nucleus population
No full textIn order to constrain the physical processes that regulate and downsize the active galactic nucleus (AGN) population, the predictions of the model for the rise of galaxies and active nuclei (MORGANA) are compared to luminosity functions (LFs) of AGNs in the optical, soft and hard X-ray bands, to the local black hole (BH)-bulge mass relation and to the observed X-ray number counts and background. We also give predictions on the accretion rate of AGNs in units of the Eddington rate and on th
Reproducing the assembly of massive galaxies within the hierarchical cosmogony
No full textIn order to gain insight into the physical mechanisms leading to the formation of stars and their assembly in galaxies, we compare the predictions of the MOdel for the Rise of GAlaxies aNd Active nuclei (MORGANA) to the properties of K- and 850-mum-selected galaxies (such as number counts, redshift distributions and luminosity functions) by combining MORGANA with the spectrophotometric model GRASIL. We find that it is possible to reproduce the K- and 850-mum-band data sets at the same time and with a standard Salpeter initial mass function, and ascribe this success to our improved modelling of cooling in DM haloes. We then predict that massively star-forming discs are common at z ~ 2 and dominate the star formation rate, but most of them merge with other galaxies within ~100 Myr. Our preferred model produces an overabundance of bright galaxies at z < 1; this overabundance might be connected to the build-up of the diffuse stellar component in galaxy clusters, as suggested by Monaco et al., but a naive implementation of the mechanism suggested in that paper does not produce a sufficient slowdown of the evolution of these objects. Moreover, our model overpredicts the number of 1010-1011Msolar galaxies at z ~ 1; this is a common behaviour of theoretical models as shown by Fontana et al.. These findings show that, while the overall build-up of the stellar mass is correctly reproduced by galaxy formation models, the `downsizing' trend of galaxies is not fully reproduced yet. This hints to some missing feedback mechanism in order to reproduce at the same time the formation of both the massive and the small galaxies
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
The QUBRICS Survey
No full textFinding the brightest QSOs at high-z is important both for constraining cosmic evolution and fundamental physics. However, in the Southern Hemisphere, the number of bright QSOs is still relatively scarce. The advent of recent databases, including SkyMapper, Gaia, DESI, offers a golden opportunity to fill in this gap. The QUBRICS survey (QUasars as BRIght beacons for Cosmology in the Southern hemisphere) has been active since 2019, exploiting these databases through machine learning techniques (e.g. CCA, PRF, XGB) and so far over 400 new, bright (i 2.5) QSOs have been spectroscopically confirmed. In this poster we highlight some of the multiple scientific applications enabled by such a dataset like (i) improving the estimate of the luminosity function; (ii) analyzing absorption features along the line of sight and (iii) improving the performance of the selection algorithms. In the future, QSOs confirmed by this survey will be the targets of subsequent studies using higher resolution spectrographs like MIKE, ESPRESSO, WINERED and will be prime targets for foreground galaxy redshift surveys with LLAMAS
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
The quasar proximity effect at redshift ~= 2.6 with the From Lines to Overdensities approach
No full textAppropriate 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
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