1,721,351 research outputs found
Two-face(s): ionized and neutral gas winds in the local Universe
No full textWe present a comprehensive study of the Na I λ5890, 5895 (Na I D) resonant lines in the Sloan Digital Sky Survey (SDSS, DR7) spectroscopic sample to look for neutral gas outflows in the local galaxies. Individual galaxy spectra are stacked in bins of stellar mass (M⋆) and star formation rate (SFR) to investigate the dependence of galactic wind occurrence and velocity as a function of the galaxy position in the SFR-M⋆ plane. While in most cases the interstellar medium (ISM) absorption and emission lines are at the galaxy systemic velocity, in massive galaxies (M⋆ > 5 × M☉) at the high SFR tail (SFR > 10-12 M☉ yr-1) we find evidence of a significant blue-shifted Na I D absorption, which we interpret as evidence of neutral outflowing gas. The occurrence of the blue-shifted absorption in the stacked spectra does not depend on the contribution of the nuclear activity as it is observed at the same significance for purely star-forming (SF) galaxies, active galactic nuclei (AGN), and composite systems at fixed SFR. We confirm, instead, for all classes of objects a clear dependence on the galaxy disc inclination: the blueshift is the largest and the Na I D equivalent width the smallest for face-on galaxies, while the absorption feature is at the systemic velocity for edge-on systems. This indicates that the neutral outflow is mostly perpendicular or biconical with respect to the galactic disc. We also compare the kinematics of the neutral gas with the ionized gas phase as traced by the [OIII]λ5007, Hα, [NII]λ6548, and [NII]λ6584 emission lines in the same galaxy spectra. Differently for the neutral gas phase, all the emission lines show evidence of perturbed kinematics only in galaxies with a significant level of nuclear activity, and they are independent of the galactic disc inclination. This would suggest that, while neutral winds originate from the galactic disc and are powered by SF feedback, ionized outflows are instead due to AGN feedback originating from the black hole accretion disc. In both the neutral and ionized gas phases, the observed wind velocities (of the order of 100-200 kms-1) suggest that the outflowing gas remains bound to the galaxy with no definitive effect on the gas reservoir
Iron Abundance in the Intracluster Medium at High Redshift
No full textWe present the analysis of the X-ray spectra of 18 distant clusters of galaxies with redshift 0.3 1 clusters, we also use deep XMM-Newton observations. Overall, these clusters probe the temperature range 3 keV less than or similar to kT less than or similar to 8 keV. Our analysis is aimed at deriving the iron abundance in the intracluster medium (ICM) out to the highest redshifts probed to date. Using a combined spectral fit of cluster sub-samples in different redshift bins, we investigate the evolution of the mean ICM metallicity with cosmic epoch. We find that the mean Fe abundance at [z] = 0.8 is Z = 0.25(-0.06)(+0.04) Z., consistent with the local canonical metallicity value, Z similar or equal to 0.3 Z., within the 1 sigma confidence level (c.l.). Medium- and low-temperature clusters (kT 1), we obtain a statistically significant detection of the Fe K line in only one cluster (Z > 0.10 Z. at the 90% c.l.). Combining all the current data sets from Chandra and XMM at z > 1, the average metallicity is measured to be [Z] = 0.21(-0.05)(+0.10) Z. (1 sigma error), thus suggesting no evolution of the mean iron abundance out to z similar or equal to 1.2
The correlation of narrow line emission and X-ray luminosity in active galactic nuclei
No full textAims.We combine emission line and X-ray luminosities for 45 sources
from the Chandra Deep Field South (CDF-S), and seven
HELLAS sources, to obtain a new sample of 52 X-ray selected
type-II active galactic nuclei (AGNs). Eighteen of our sources are very luminous with a typical,
absorption-corrected 2–10 keV luminosity of erg s-1 (type-II QSOs).
Methods.
We compare the emission line properties of the new sources
with emission line and X-ray luminosities of known low redshift, mostly lower luminosity AGNs
by using a composite spectrum.
Results.
We find that / and / decrease with L(2–10 keV) such that
/ .
The trend was already evident, yet neglected in past low redshift samples.
This lead to erroneous calibration of the line-to-X-ray luminosity in earlier AGN samples.
The analysis of several type-I samples shows the same trend with a similar slope
but a median / which is larger by a factor of about two compared with optically selected
type-II samples. We interpret this shift as due to additional reddening
in type-II sources and comment in general on the very large extinction in many type-II objects
and the significantly smaller average reddening of the SDSS type-II AGNs.
The decrease of / with L(2–10 keV) is
large enough to suggest that a significant fraction of high luminosity
high redshift type-II AGNs have very weak emission lines that may have
escaped detection in large samples. A related decrease of EW([O ii
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
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