1,721,253 research outputs found
An increase in black hole activity in galaxies with kinematically misaligned gas
No full textExternal accretion events such as a galaxy merger or the accretion of gas from the immediate environment of a galaxy can create a large misalignment between the gas and the stellar kinematics. Numerical simulations have suggested that misaligned structures may promote the inflow of gas to the nucleus of the galaxy and the accretion of gas by the central supermassive black hole. We show for the first time that galaxies with a strong misalignment between the ionized gas and stellar kinematic angles have a higher observed fraction of active black holes than galaxies with aligned rotation of gas and stars. The increase in black hole activity suggests that the process of formation and/or the presence of misaligned structures are connected with the fuelling of active supermassive black holes
SPITZER-IRS HIGH-RESOLUTION SPECTROSCOPY OF THE 12 μm SEYFERT GALAXIES. II. RESULTS FOR THE COMPLETE DATA SET
Full text linkWe present the Spitzer 10-37um IRS high resolution (R~600) spectroscopic
survey of the Seyfert galaxies of the 12 micron Galaxy Sample. The new spectra
of 61 galaxies, with those already published, gives us a total of 91 12micron
Seyfert galaxies observed, out of 112. We use an improved AGN classification
for Seyfert galaxies: instead of the type 1 and 2 classes, we use the
spectropolarimetric data to divide them into "AGN 1" and "AGN 2", where AGN 1's
include all broad-line objects, including the Seyfert 2's showing hidden broad
lines in polarized light, while AGN 2's contains only Seyferts with no
detectable broad lines at all. We present various mid-IR observables and we
find that these properties characterize the AGN 1's objects as a single family,
with strongly AGN-dominated spectra. In contrast, the AGN 2's can be divided in
two groups, the first one with properties similar to the AGN 1's and the second
similar to the non-Seyfert galaxies, such as LINERs or starburst galaxies. We
computed a semianalytical model to estimate the AGN and the starburst
contributions to the mid-IR galaxy emission at 19um. We find that AGN 1 have an
AGN contribution >73% and AGN 2 >45% of their total emission at 19um. The
detection of [NeV] lines is an almost perfect signature of energy production by
an AGN. We present mean spectra of the various AGN categories. We derive the
first local luminosity functions for the mid-infrared lines and the PAH
feature. No statistical difference is found in the space densities for Seyfert
1's and 2's, nor for the new classes of AGN 1's and 2's. The global output of
accretion-powered galactic nuclei in the local universe is derived from the
correlation between [NeV] line and the nonstellar IR continuum luminosity
Mapping the active galactic nucleus effects on the stellar and gas properties of NGC 5806
No full textIt is commonly accepted that active galactic nuclei (AGNs) have a strong impact upon the evolution of their host galaxies, but the processes by which they do so are not fully understood. We aim to further the understanding of AGN feeding and feedback by examining an active galaxy using spatially resolved spectroscopy. We analyze integral field spectroscopy of the active galaxy NGC 5806, obtained using the Very Large Telescope Multi-Unit Spectroscopic Explorer. We map the dynamics of gas and stars, as well as gas optical emission line fluxes throughout the central 8 × 8 kpc2 of the galaxy. We use emission line ratios to map gas metallicity and identify regions of gas excitation dominated by AGN/shocks or star formation. We also determine the average stellar population age and metallicity, and model the rotation and dynamics of the galaxy. We find that NGC 5806 has a star-forming circumnuclear ring, with a projected radius of ~400 pc. The dynamics of this galaxy are driven by a large-scale bar, which transports gas from the spiral arm to the central ring and potentially fuels the AGN. We also observe AGN-dominated gas excitation up to 3.3 kpc away from the center of the galaxy, showing the extended AGN effect on the gas in the central regions of the galaxy
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
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Supermassive Black Hole Growth During The Peak Of Cosmic Star Formation
Full text linkMassive galaxies in the nearby universe all show evidence of a central SupermassiveBlack Hole. The black holes are seen to grow over time by accretion of gasfrom their host galaxy, a phenomenon referred to as an Active Galactic Nucleus.This process is believed to be fundamental to the observed correlations betweenblack hole mass and properties of the host galaxies. We have a more limited andbiased understanding of the growth of supermassive black holes in more ‘typical’galaxies at z ∼ 1 − 2. In this work, we search for Active Galactic Nuclei in apopulation of star-forming galaxies spanning a mass range of M∗ ∼ 10^7−10^12 M⊙at 0.62 < z < 2.39, during the peak of cosmic star formation and massive blackhole growth. Our data are drawn from the WFC3 Infrared Spectroscopic Parallels(WISP) survey, for which we designed and implemented a suite of data analysisroutines for discovering and measuring star-forming galaxies and active galacticnuclei. We find a sample of 50 active galactic nuclei, identified by their strong,rest-frame optical, emission-line ratios. We find that growing supermassive blackholes in low-mass galaxies at z > 1 either make up a greater fraction of theirgalaxies’ masses than those in massive galaxies, or perhaps emit a greater fractionof their energy in [O III]
The Legacy of the AKARI Infrared Space Telescope: Polycyclic Aromatic Hydrocarbon Dust Emission as a Star Formation Rate Indicator
Full text linkPolycyclic aromatic hydrocarbon (PAH) dust emission has been proposed as an effective extinction-independent star formation rate (SFR) indicator in the mid-infrared (MIR), but is sensitive to conditions in the interstellar medium. This thesis is based on MIR photometric data from the AKARI/Infrared Camera (IRC), which provides a representative and unbiased sample for studying the effects of metallicity, starburst intensity, and active galactic nuclei (AGN) on PAH dust emission. Our observations include follow-up, rest-frame optical spectra of 443 galaxies within the AKARI North Ecliptic Pole survey that have IRC detections from 7—24 m. We use optical emission line diagnostics to measure gas-phase metallicity, to classify the source of ionizing photons, to measure dust extinction, and to infer star formation rate (SFR) based on H and [O II] emission line luminosities. We show that the PAH 6.2 m and PAH 7.7 m luminosities ( and , respectively) derived using multi-wavelength model fits are consistent with those derived from slitless spectroscopy within 0.2 dex. We find that and correlate linearly with the 24 m-dust corrected H luminosity only for normal, main-sequence galaxies. Assuming multi-linear fits, we quantify the additional dependencies on gas-phase metallicity and starburst intensity, which we use to correct our PAH SFR calibrations at $
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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