1,720,974 research outputs found
Near-side supernovae driven winds from the Large Magellanic Cloud
No full textMassive amounts of gaseous material are being ejected from the nearby Large Magellanic Cloud galaxy (LMC). With the LMC at only one Milky Way diameter away, we use this excellent opportunity to explore the ejected materials cycle in detail. The star-forming lifetime of a galaxy is dependent on both the gas supply of the galaxy and the galactic processes that occur within. Therefore, it is essential to study this wind in detail to understand the properties that will influence the LMCs evolution and the surrounding environment. We have combined ground-based and space-based observations to (1) map the near-side galactic wind of the LMC, (2) determine the morphology and extent of this gaseous outflow and (3) estimate a mass for the outflow. Understanding the properties of this galactic wind will provide invaluable information about galaxy evolution and surrounding environments, galactic feedback, and the LMCs possible influence on the Milky Way
Star-formation activity in low-mass disk galaxies
No full textInteraction between galaxies is of critical importance to the growth and evolution of galaxies. Due to the lack of studies on interactions between low-mass galaxies, it is still uncertain that how low-mass galaxies evolve during an interacting procedure. This investigation will explore how the internal star-formation activities of low-mass disk galaxies are influenced by the outer environment. The interaction-induced enhancement of star formation rate in diverse galaxy systems will be examined. This work presented here is the first attempt to systematically study the evolution of low-mass disk galaxies, it is also a pioneer of a statistical study on low-mass interacting galaxy systems. This investigation is based on data from the fourth-generation Sloan Digital Sky Survey (SDSS- IV) / Mapping Nearby Galaxies at Apache Point Observatory (MaNGA)
Galactic winds of the Large Magellanic Cloud
No full textIn the Large Magellanic Cloud (LMC), galaxy interactions have triggered intense star formation throughout its disk. Using UV Hubble Space Telescope (HST) absorption-line observations towards an AGN and a LMC disk star projected only 100 pc away, we find gaseous outflows that are relatively symmetric in kinematics and properties on both sides of the galaxy's disk. These results when combined with previous studie provide compelling evidence that stellar activity drives a global, large-scale wind that permeates from its entire disk. As the LMC is the only galaxy where the connection between the stellar activity and galactic feedback can be fully resolved, these results provide insight into the effects of stellar feedback in further away galaxies
Galactic winds of the Large Magellanic Cloud
No full textIn the Large Magellanic Cloud (LMC), galaxy interactions have triggered intense star formation throughout its disk. Using UV Hubble Space Telescope (HST) absorption-line observations towards an AGN and a LMC disk star projected only 100 pc away, we find gaseous outflows that are relatively symmetric in kinematics and properties on both sides of the galaxy's disk. These results—when combined with previous studies—provide compelling evidence that stellar activity drives a global, large-scale wind that permeates from its entire disk. As the LMC is the only galaxy where the connection between the stellar activity and galactic feedback can be fully resolved, these results provide insight into the effects of stellar feedback in further away galaxies
Galactic Gas Flows and their Role in the History and Evolution of the Magellanic System
No full textWithin our Galactic backyard, the Magellanic System, composed of the Large and Small Magellanic Clouds, is exchanging millions to billions of solar masses worth of material to the Milky Way. In two different studies, we explored this exchange and its impact on the Galactic environment. In the first study, a galactic outflow has erupted due to supernovae explosions within the disk. We present the first spectroscopically resolved H-alpha emission map of this wind. Kinematically, we find that the diffuse gas in the warm-ionized phase of the wind persists at both low (100km/s) velocities, relative to the LMC's HI disk. Furthermore, we find that the high-velocity component spatially aligns with the most intense star-forming region, 30~Doradus. We, therefore, conclude that this high-velocity material traces an active outflow. This wind is ejecting an estimated log(Mionized/Mo)=7.51 +/- 0.15 worth of material off the near-side of the galaxy. The second study observes tidally stripped gas that leads the LMC's orbit. This material formed into a massive complex called the Leading Arm that contains multiple sub-structures of gas. We investigate the physical and ionization conditions of this structure using Hubble Space Telescope/Cosmic Origins Spectrograph UV absorption-line and 21\,cm \hi\ emission-line observations along 13 sightlines. Additionally, we use Cloudy radiative transfer modeling to estimate their average temperatures, densities, ionization fractions, and thermal pressures. We find that most Leading Arm sub-structures exhibit multiple absorbers along their lines of sight, indicating a complex three-dimensional structure. Using the ionization fractions, we estimate that the total (neutral plus ionized) hydrogen mass of the LA sub-structures is M_H=3.0x10^8 Mo across a velocity range of +100 < vLSR < +240 km/s. In both studies, the material at play has the potential to fall onto the Milky Way and produce the future generation of solar systems
The Effects of Environment on Galaxy Evolution in Mapping Nearby Galaxies at Apache Point Observatory (MaNGA)
No full textGalaxy interactions and mergers are known to have been a fundamental process in the hierarchical formation of the Universe. These galaxy interactions first occurred between low-mass galaxies, analogous to today's dwarf galaxies. There have been a lack of studies on dwarf-dwarf galaxy interactions due to the difficulties in observing them. The development of better technology and telescopes has allowed the field to begin to gather the much-needed information on these events. This pilot study represents the first to examine the effects of dwarf-dwarf galaxy interactions on star-formation enhancement and star-formation rates using spatially and spectroscopically resolved data from the SDSS-IV MaNGA Survey. Two samples are studied to this effect: a sample of nine dwarf galaxies known to have close dwarf companions and a sample of fifteen dwarf galaxies known to be extremely isolated (~ 1 Mpc) from any other galaxies. The ionization conditions of each galaxy is studied using diagnostic diagrams which can classify regions within the galaxy as star-forming. The percentage of surface area which is star-forming and the central star-formation rate is calculated for each galaxy in both samples. We find that star formation is enhanced by almost a factor of four within the galaxies in the paired sample compared to those in the isolated sample. The methods developed for this study can be applied to much larger samples in the future once the data become available, thus allowing for further study of these crucial dwarf-dwarf galaxy interactions
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
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
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