1,721,146 research outputs found
Integral field spectroscopy of NGC 2855 and NGC 7049
No full textWe present the ionized gas bidimensional velocity field of two spiral galaxies (NGC 2855 and NGC 7049) which show an S-distortion of the isovelocities. We performed models of the velocity field in order to investigate the possible presence of an inner polar disk which generate such a kinematic behaviour, or the presence of a strong internal warp of the gaseous disk. The decomposition of the surface brightness map of NGC 7049 seems to indicate the presence of an orthogonal decoupled component, while the case of NGC 2855 seems to be better explained in terms of a strong central warp of the gaseous disk
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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 search for inner polar disks with integral field spectroscopy: the case of NGC 2855 and NGC 7049
Get PDFContext: The presence of non-circular and off-plane gas motion is frequently observed in the inner regions of disk galaxies. Aims: With integral-field spectroscopy we have measured the surface-brightness distribution and kinematics of the ionized gas in NGC 2855 and NGC 7049. These two early-type spiral galaxies were selected as possibly hosting a kinematically-decoupled gaseous component in orthogonal rotation with respect to the galaxy disk. Methods: We have modeled the ionized-gas kinematics and distribution of both galaxies assuming that the gaseous component is distributed either on two orthogonally-rotating disks or in a single and strongly warped disk. Results: In both galaxies the velocity field and distribution of the inner gas are consistent with the presence of an inner polar disk. In NGC 2855 it correponds to the innermost and strongly warped portion of the main disk. In NGC 7049 it is a central and geometrically-decoupled disk, which is nested in the main disk
NGC 4435: a bulge-dominated galaxy with an unforeseen low-mass central black hole
Get PDFWe present the ionized gas kinematics of the SB0 galaxy NGC 4435 from spectra obtained with the Space Telescope Imaging Spectrograph. This galaxy has been selected on the basis of its ground-based spectroscopy, for displaying a position-velocity diagram consistent with the presence of a circumnuclear Keplerian disc rotating around a supermassive black hole (SMBH). We obtained the Hα and [NII]λ6583 kinematics in the galaxy nucleus along the major axis and two parallel offset positions. We built a dynamical model of the gaseous disc taking into account the whole bi-dimensional velocity field and the instrumental setup. For the mass of the central SMBH, we found an upper limit of 7.5 × 10^6 M_solar at the 3σ level. This indicates that the mass of the SMBH of NGC 4435 is lower than the one expected from the M_BH-σ_c (5 × 10^7 M_solar) and near-infrared M_BH-L_bulge (4 × 10^7 M_solar) relationships
Variations on the Author
Get PDF“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
Get PDFWe 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
The counter-rotating stellar core of NGC 4494
Get PDFContext. Kinematically decoupled cores (KDCs) are often found in the centers of early-type galaxies. Aims. We aim to investigate the kinematics, structure, and stellar populations of the KDC residing in the early-type galaxy NGC 4494 to understand its formation. Methods. We used long-slit spectroscopic data obtained with the FORS2 instrument on the VLT to measure the stellar kinematics and stellar populations. We performed a spectroscopic decomposition to disentangle the properties of the KDC from those of the host galaxy and construct models of the observed rotation curve. Results. The rotation curve is characterized by two symmetric dips at |R| = 6, where the rotation velocity drops to zero. Contrary to previous studies that explained the decoupled structure as a rapidly co-rotating disk, our analysis clearly shows that it is a counter-rotating component. A counter-rotating core is indeed needed to reproduce the observed dip in the velocity curve. The properties of the stellar populations of the decoupled core and the main galaxy are very similar: old stars (12-13 Gyr) with slightly super-solar metallicities (0-<-[Z/H]< 0.15 dex) and α-enhanced (0-<-[α/Fe]< 0.15 dex). Conclusions. Our results indicate that the counter-rotating component is a disk of about 1 kpc in diameter that is obscured by dust in the central 0.12 kpc. The properties of its stellar populations suggest that it formed from the same material as the main stellar body of the host galaxy. This could have happened via internal processes such as the precession of a pre-existing rotating core, or, alternatively, via gas accretion in retrograde orbits followed by star formation. In the latter scenario, the accretion event occurred almost simultaneously with the formation of the galaxy, using material that had the same composition as the gas from which the stars in the main body of the galaxy were formed
Disentangling the kinematics and stellar populations of counter-rotating stellar discs in galaxies
No full textSpectroscopic VIMOS/IFU observations are presented for three galaxies known to host two stellar counter-rotating discs of comparable sizes. For the first time both the kinematics and stellar population properties of the two counter-rotating discs in the observed galaxies were separated and measured. The secondary, less massive, stellar component rotates in the same direction as the ionised gas and is on average younger and less metal-rich than the main galaxy disc. These results support the scenario of gas accretion followed by star formation as the origin for large counter-rotating stellar discs in galaxies, and set an upper limit of 44% to those formed by binary galaxy mergers
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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