1,721,244 research outputs found
On the existence of bright IR galaxies at z > 2: Tension between Herschel and SCUBA-2 results?
Full text linkRecent derivations of the galaxy star formation rate density (SFRD) obtained from submillimetre (sub-mm) surveys (e.g. SCUBA-2) show a tension with previous works based on Herschel and multi-wavelength data. Some of these works claim that the SFRD derived by pushing the Herschel surveys beyond z ≃ 2 are incorrect. However, the current sub-mm surveys obtained from SCUBA-2 data and the methods used to construct the total infrared (IR) luminosity function (LF) and the SFRD could be affected by some limitations. Here, we show how these limitations (i.e. selection bias and incompleteness effects) might affect the total IR LF, making the resulting dusty galaxy evolution of difficult interpretation. In particular, we find that the assumed spectral energy distribution (SED) plays a crucial role in the total IR LF derivation; moreover, we confirm that the long-wavelength (e.g. 850-μm) surveys can be incomplete against 'warm' SED galaxies, and that the use of a wide spectral coverage of IR wavelengths is crucial to limit the uncertainties and biases
CO luminosity function from Herschel-selected galaxies and the contribution of AGN
Full text linkWe derive the carbon monoxide (CO) luminosity function (LF) for different rotational transitions [i.e. (1-0), (3-2), (5-4)] starting from the Herschel LF by Gruppioni et al. and using appropriate LCO-LIR conversions for different galaxy classes. Our predicted LFs fit the data so far available at z ≈ 0 and 2. We compare our results with those obtained by semi-analytical models (SAMs): while we find a good agreement over the whole range of luminosities at z ≈0, at z≈1 and z≈2, the tension between our LFs and SAMs in the faint and bright ends increases. We finally discuss the contribution of luminous active galactic nucleus (LX > 1044 erg s-1) to the bright end of the CO LF concluding that they are too rare to reproduce the actual CO LF at z ≈ 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
Extragalactic Source Counts in the Spitzer 24 Micron Band: What Do We Expect from ISOCAM 15 Micron Data and Models?
No full textThe comparison between the new Spitzer data at 24 µm and the previous ISOCAM data at 15 µm is a key tool to understand galaxy properties and evolution in the infrared and to interpret the observed number counts, since the combination of Spitzer with the Infrared Space Observatory cosmological surveys provides for the first time the direct view of the universe in the infrared up to z gsim 2. We present the prediction in the Spitzer 24 µm band of a phenomenological model for galaxy evolution derived from the 15 µm data. Without any "a posteriori" update, the model predictions seem to agree well with the recently published 24 µm extragalactic source counts, suggesting that the peak in the 24 µm counts is dominated by "starburst" galaxies like those detected by ISOCAM at 15 µm but at higher redshifts (1 lesssim z lesssim 2 instead of 0.5 lesssim z lesssim 1.5)
ELAIS-South: The nature and evolution of galaxies and AGN in the mid-infrared
No full textWe present the results from the spectroscopic identifications of the ELAIS sources in the southern fields S1 and S2. Two main extragalactic classes have been found: z < 0.5 star-forming galaxies (similar to75%), and AGN (similar to25%). similar to20% are dust enshrouded starburst galaxies [e(a) spectral. All the galaxies appear more dust extincted in the optical than nearby normal galaxies. The evolution of galaxies is fitted by a strong evolution for only a fraction of the whole population. AGN1 evolves according to a pure luminosity evolution, while no evolution is found for the AGN2
Modelling galaxy and AGN evolution in the infrared: black hole accretion versus star-formation activity
No full textWe present a new backward evolution model for galaxies and active galactic nuclei (AGNs) in the infrared (IR). What is new in this model is the separate study of the evolutionary properties of different IR populations (i.e. spiral galaxies, starburst galaxies, low-luminosity AGNs, 'unobscured' type 1 AGNs and 'obscured' type 2 AGNs) defined through a detailed analysis of the spectral energy distributions (SEDs) of large samples of IR-selected sources. The evolutionary parameters have been constrained by means of all the available observables from surveys in the mid- and far-IR (source counts, redshift and luminosity distributions, luminosity functions). By decomposing the SEDs representative of the three AGN classes into three distinct components (a stellar component emitting most of its power in the optical/near-IR, an AGN component due to the hot dust heated by the central black hole peaking in the mid-IR, and a starburst component dominating the far-IR spectrum), we have disentangled the AGN contribution to the monochromatic and total IR luminosity emitted by different populations considered in our model from that due to star formation activity. We have then obtained an estimate of the total IR luminosity density [and star formation density (SFD) produced by IR galaxies] and the first ever estimate of the black hole mass accretion density (BHAR) from the IR. The derived evolution of the BHAR is in agreement with estimates from X-rays, though the BHAR values we derive from the IR are slightly higher than the X-ray ones. Finally, we have simulated source counts, redshift distributions, and SFD and BHAR that we expect to obtain with the future cosmological surveys in the mid-/far-IR that will be performed with the JWST-MIRI and SPICA-SAFARI. Outputs of the model are available online
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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