1,721,147 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
The environmental properties of radio-emitting AGN
No full textWe study the environmental properties of z less than or similar to 1.2
radio-selected active galactic nuclei (AGNs) belonging to the similar to
2 deg(2) of the COSMOS field, finding that about 20 per cent of them
appear within overdense structures. AGNs with P-1.4 GHz > 10(23.5) W
Hz(-1) sr(-1) are twice more likely to be found in clusters with respect
to fainter sources (similar to 38 per cent vs similar to 15 per cent),
just as radio-selected AGNs with stellar masses M-* > 10(11) M-circle
dot are twice more likely to be found in overdense environments with
respect to objects of lower mass (similar to 24 per cent vs similar to
11 per cent). Comparisons with galaxy samples further suggest that
radio-selected AGN of large stellar mass tend to avoid underdense
environments more than normal galaxies with the same stellar content.
Stellar masses also seem to determine the location of radio-active AGN
within clusters: similar to 100 per cent of the sources found as
satellite galaxies have M* < 10(11.3) M-circle dot, while similar to
100 per cent of the AGNs coinciding with a cluster central galaxy have
M* > 10(11) M-circle dot. No different location within the cluster is
instead observed for AGN of various radio luminosities. Radio AGN, which
also emit in the Mid-Infrared show a marked preference to be found as
isolated galaxies (similar to 70 per cent) at variance with those also
active in the X-ray that all seem to reside within overdensities. What
emerges from our work is a scenario whereby physical processes on sub-pc
and kpc scales (e.g. emission, respectively, related to the AGN and to
star formation) are strongly interconnected with the large-scale
environment of the AGN itself
A census of radio-selected AGNs on the COSMOS field and of their FIR properties
No full textWe use the new catalogue by Laigle et al. to provide a full census of VLA-COSMOS radio sources.We identify 90 per cent of such sources and sub-divide them into active galactic nuclei (AGNs) and star-forming galaxies on the basis of their radio luminosity. The AGN sample is complete with respect to radio selection at all z ≲ 3.5. Out of 704 AGNs, 272 have a counterpart in the Herschel maps. By exploiting the better statistics of the new sample, we confirm the results of Magliocchetti et al.: the probability for a radio-selected AGN to be detected at far-infrared (FIR) wavelengths is both a function of radio luminosity and redshift, whereby powerful sources are more likely FIR emitters at earlier epochs. Such an emission is due to star-forming processes within the host galaxy. FIR emitters and non-FIR emitters only differentiate in the z ≲ 1 universe. At higher redshifts, they are indistinguishable from each other, as there is no difference between FIR-emitting AGNs and star-forming galaxies. Lastly, we focus on radio AGNs which show AGN emission at other wavelengths. We find that midinfrared (MIR) emission is mainly associated with ongoing star formation and with sources which are smaller, younger and more radio luminous than the average parent population. X-ray emitters instead preferentially appear in more massive and older galaxies. We can therefore envisage an evolutionary track whereby the first phase of a radio-active AGN and of its host galaxy is associated with MIR emission, while at later stages the source becomes only active at radio wavelengths and possibly also in the X-ray
The dust and cold gas content of local star-forming galaxies
Full text linkWe use dust masses (Mdust) derived from far-infrared data and molecular gas masses (Mmol) based on CO luminosity to calibrate proxies based on a combination of the galaxy Balmer decrement, disc inclination, and gas metallicity. We use such proxies to estimate Mdust and Mmol in the local SDSS sample of star-forming galaxies (SFGs). We study the distribution of Mdust and Mmol along and across the main sequence (MS) of SFGs. We find that Mdust and Mmol increase rapidly along the MS with increasing stellar mass (M∗), and more marginally across the MS with increasing SFR (or distance from the relation). The dependence on M∗ is sub-linear for both Mdust and Mmol. Thus, the fraction of dust (fdust) and molecular gas mass (fmol) decreases monotonically towards large M∗. The star formation efficiency (SFE, inverse of the molecular gas depletion time) depends strongly on the distance from the MS and it is constant along the MS. As nearly all galaxies in the sample are central galaxies, we estimate the dependence of fdust and fgas on the host halo mass and find a tight anticorrelation. As the region where the MS is bending is numerically dominated by massive haloes, we conclude that the bending of the MS is due to a lower availability of molecular gas mass in massive haloes rather than a lower efficiency in forming stars
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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