1,720,968 research outputs found
The Lyα and Continuum Origins Survey. I. Survey Description and Lyα Imaging
No full textLe Reste, Alexandra et al.-- Full list of authors: Le Reste, Alexandra; Scarlata, Claudia; Hayes, Matthew J.; Melinder, Jens; Saldana-Lopez, Alberto; Smith, Aaron; Runnholm, Axel; Lin, Yu-Heng; Amorín, Ricardo O.; Atek, Hakim; Borthakur, Sanchayeeta; Carr, Cody A.; Fleming, Brian; Flury, Sophia R.; Giavalisco, Mauro; Henry, Alaina; Jaskot, Anne E.; Ji, Zhiyuan; Jung, Intae; Leclercq, Floriane; Marques-Chaves, Rui; McCandliss, Stephan R.; Oey, M. S.; Östlin, Göran; Ravindranath, Swara; Schaerer, Daniel; Thuan, Trinh X.; Xu, XinfengUnderstanding the mechanisms driving the escape of ionizing or Lyman continuum (LyC) emission from the interstellar medium of galaxies is necessary to constrain the evolution of reionization and the sources responsible for it. While progress has been made in identifying the global galaxy properties linked to the ionizing escape fraction fescLyC , little is currently known about how spatially resolved galaxy properties impact it. We present Hubble Space Telescope (HST) imaging data obtained in the Lyα and Continuum Origins Survey (LaCOS). LaCOS consists of HST imaging covering rest-frame optical and UV bands for a subsample of 42 galaxies in the Low redshift Lyman Continuum Survey, including 22 LyC emitters ( fescLyC=0.01-0.49 ). Here, we describe the sample, observations, and data reduction, and investigate connections between global and sub-kiloparsec Lyα emission and fescLyC . We confirm the correlation between fescLyC and EWLyα, and the anticorrelation with r50, when using values obtained via global photometry. We also find correlations previously found with spectroscopy with global photometric LLyα, fescLyα , ΣSFR, and fescLyC , but with a smaller degree of correlations ( ∣Δτ∣¯∼0.1 ). We find correlations are strongest between Lyα observables (LLyα, EWLyα) and fescLyC when measured in a small aperture around the brightest UV source in each galaxy. We interpret these results as evidence that LyC photons escaping on the line of sight are contributed by a small number of UV-bright compact regions in most galaxies in LaCOS. © 2025. The Author(s).This research is based on observations made with the NASA/ESA HST obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–26555. These observations are from HST GO programs 17069, 14131, and 11107. A.L.R. acknowledges support from HST GO-17069. M.J.H. is supported by the Swedish Research Council (Vetenskapsrådet) and is a fellow of the Knut and Alice Wallenberg Foundation. A.S.L. acknowledges support from the Knut and Alice Wallenberg Foundation. S.B. acknowledges support from NSF grant 2408050. F.L. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. C3UBES-101107619.Peer reviewe
Neutral gas properties of high-redshift analog galaxies : 21cm observations of Lyα and LyC-emitting galaxies
No full textNeutral hydrogen (HI) is the most abundant baryonic element and a crucial component of galaxies. In the early universe, the interaction between neutral gas and the light produced by galaxies is thought to have given rise to cosmological reionization. During this last major phase transition of the Universe, the bulk of HI within the intergalactic medium (IGM) was ionized. However, observational constraints limit our understanding of the interplay between the radiation produced by galaxies and their neutral gas, and that of the physical processes that caused this important cosmological period. Another poorly understood mechanism is the one that drives the escape of Lyman-α (Lyα) emission from star-forming galaxies and shapes the line profile of this well-used tracer of galaxies at high redshift. To fully answer these questions, direct observations of the neutral gas content and distribution of Lyα emitters are needed. This thesis presents 21cm observations of the neutral gas reservoirs of rare local galaxies that are analogous to objects in the early universe. We have observed the neutral gas of Haro 11, the closest known ionizing radiation (Lyman Continuum, LyC) leaking galaxy. This 21cm observation was the first to successfully map the neutral gas distribution of a confirmed LyC emitter. We observed a strongly asymmetric neutral gas distribution resulting from a merger event, with the bulk of the HI mass offset from the regions producing LyC radiation in the galaxy. By decreasing the column density of gas on large scales, this HI distribution has facilitated the escape of ionizing radiation from the center of the galaxy to the IGM. We have also observed the neutral gas content and distribution of local Lyα-emitting galaxies on a variety of angular scales. We mapped the neutral gas at scales that can be compared to those characterizing Lyα emission in two galaxies, and supplemented the data with integral field spectroscopic observations tracing ionized gas and dust. Additionally, we reduced low angular resolution 21cm observations of 37 galaxies in the Lyman Alpha Reference Samples. We found clear evidence of interaction in most of the galaxies in the samples (~60%), indicating that mergers play an important role in the Lyα escape from galaxies. We found that global HI properties did not correlate well with any metric quantifying Lyα emission, although different classes of Lyα-emitters were distributed differently around HI scaling relations. This indicates that star-forming galaxies with low neutral gas content have a higher chance of emitting strongly in Lyα, but ultimately, neutral gas regulates the escape of Lyα emission on small scales. 21cm studies of both Lyα and LyC emitters conducted in this thesis have demonstrated that galaxy interactions play an important role in the escape of ultraviolet (UV) radiation from local galaxies. By perturbing the neutral gas content of galaxies and enhancing their star formation rate, these interactions are interesting mechanisms that facilitate the escape of UV radiation. According to cosmological models, galaxy mergers occurred more frequently in the early universe. Assessing the contribution of environment and galaxy interactions at high redshift will be essential to fully understand the first billion years of our universe
Neutral gas properties of high-redshift analog galaxies : 21cm observations of Lyα and LyC-emitting galaxies
No full textNeutral hydrogen (HI) is the most abundant baryonic element and a crucial component of galaxies. In the early universe, the interaction between neutral gas and the light produced by galaxies is thought to have given rise to cosmological reionization. During this last major phase transition of the Universe, the bulk of HI within the intergalactic medium (IGM) was ionized. However, observational constraints limit our understanding of the interplay between the radiation produced by galaxies and their neutral gas, and that of the physical processes that caused this important cosmological period. Another poorly understood mechanism is the one that drives the escape of Lyman-α (Lyα) emission from star-forming galaxies and shapes the line profile of this well-used tracer of galaxies at high redshift. To fully answer these questions, direct observations of the neutral gas content and distribution of Lyα emitters are needed. This thesis presents 21cm observations of the neutral gas reservoirs of rare local galaxies that are analogous to objects in the early universe. We have observed the neutral gas of Haro 11, the closest known ionizing radiation (Lyman Continuum, LyC) leaking galaxy. This 21cm observation was the first to successfully map the neutral gas distribution of a confirmed LyC emitter. We observed a strongly asymmetric neutral gas distribution resulting from a merger event, with the bulk of the HI mass offset from the regions producing LyC radiation in the galaxy. By decreasing the column density of gas on large scales, this HI distribution has facilitated the escape of ionizing radiation from the center of the galaxy to the IGM. We have also observed the neutral gas content and distribution of local Lyα-emitting galaxies on a variety of angular scales. We mapped the neutral gas at scales that can be compared to those characterizing Lyα emission in two galaxies, and supplemented the data with integral field spectroscopic observations tracing ionized gas and dust. Additionally, we reduced low angular resolution 21cm observations of 37 galaxies in the Lyman Alpha Reference Samples. We found clear evidence of interaction in most of the galaxies in the samples (~60%), indicating that mergers play an important role in the Lyα escape from galaxies. We found that global HI properties did not correlate well with any metric quantifying Lyα emission, although different classes of Lyα-emitters were distributed differently around HI scaling relations. This indicates that star-forming galaxies with low neutral gas content have a higher chance of emitting strongly in Lyα, but ultimately, neutral gas regulates the escape of Lyα emission on small scales. 21cm studies of both Lyα and LyC emitters conducted in this thesis have demonstrated that galaxy interactions play an important role in the escape of ultraviolet (UV) radiation from local galaxies. By perturbing the neutral gas content of galaxies and enhancing their star formation rate, these interactions are interesting mechanisms that facilitate the escape of UV radiation. According to cosmological models, galaxy mergers occurred more frequently in the early universe. Assessing the contribution of environment and galaxy interactions at high redshift will be essential to fully understand the first billion years of our universe
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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