1,721,060 research outputs found
Examining the neutral circumgalactic medium of NGC 891 and NGC 4565
No full textWork done by Das 2020 (D20 \cite{Das2020b}) shows, along the minor axis, the velocity is consistent with an inflow/fountain in NGC 891 and an inflow/outflow in NGC 4565. Previous work done by Das 2024 (D24\cite{DasandRickel2024}) along the major axis shows the diffuse \hi is a co-rotating CGM or the outer part of an extended HI disk. From D20 and D24, the star formation of NGC 4565 can be sufficiently explained including the circumgalactic \hi, the depletion time, and the accretion rate. However, most accreting material in NGC 891 is missing. To obtain a 360\deg view, we probe the diffuse neutral circumgalactic medium (CGM) along the off axes of NGC 891 and NGC 4565 out to ~30 kpc using the Green Bank Telescope (GBT). We detect HI with varying spectral shapes, velocity widths, and column densities with a sensitivity of 10 cm % 1 sigma. We compare our single-dish detections to the interferometric maps from the Westerbork Synthesis Radio Telescope (WSRT) obtained as part of the HALOGAS survey. We find that all of the emission detected by the GBT cannot be explained by the emission seen in WSRT maps.No embargoAcademic Major: Astronomy and AstrophysicsAcademic Major: Physic
Chandra Discovery of a Tree in the X-Ray Forest toward PKS 2155-304: The Local Filament?
No full textFlares in the changing look AGN Mrk 590. I: The UV response to X-ray outbursts suggests a more complex reprocessing geometry than a standard disk
No full textMrk 590 is a known changing-look AGN which almost turned off in 2012, and then in 2017 partially re-ignited into a repeat flaring state, unusual for an AGN. Our \emph{Swift} observations since 2013 allow us to characterise the accretion-generated emission and its reprocessing in the central engine of a changing-look AGN. The X-ray and UV variability amplitudes are higher than those typically observed in `steady-state' AGN at similar moderate accretion rates; instead, the variability is similar to that of highly accreting AGN. The unusually strong X-ray to UV correlation suggests that the UV-emitting region is directly illuminated by X-ray outbursts. We find evidence that the X-rays are reprocessed by two UV components, with the dominant one at 3 days and a faint additional reprocessor at near-zero lag. However, we exclude a significant contribution from diffuse broad line region continuum, known to contribute for bona-fide AGN. A near-zero lag is expected for a standard `lamp-post' disk reprocessing model with a driving continuum source near the black hole. That the overall UV response is dominated by the 3-day lagged component suggests a complicated reprocessing geometry, with most of the UV continuum not produced in a compact disk, as also found in recent studies of NGC 5548 and NGC 4151. Nonetheless, the observed flares display characteristic timescales of 100 rest-frame days, consistent with the expected thermal timescale in an accretion disk
The NGC 3341 minor merger: a panchromatic view of the active galactic nucleus in a dwarf companion
No full text"We present X-ray (Chandra), radio (Expanded Very Large Array and European VLBI Network) and archival optical data of the triple-merging system in NGC 3341. Our panchromatic analysis confirms the presence of a Seyfert 2 active galactic nucleus (AGN) in NGC 3341B, one of the secondary dwarf companions. On the other hand, the nucleus of the primary galaxy, consistent with a star-forming region of a few solar masses per year, and NGC 3341C are very unlikely to host an AGN. We therefore suggest that NGC 3341 is an exceptional example of an AGN triggered in the satellite galaxy of a minor-merging system. The existence of such a system can have important implications in the models of hierarchical growth of structures. Further observational and theoretical efforts on NGC 3341 and potentially similar sources are needed in order to understand the role of minor mergers on the onset of AGN activity, and in the evolution of massive galaxies.
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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