382 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
Le système de retraite et l'équité intergénérationnelle
No full textThe Pension System and Intergenerational Equity
by Alexandra Tragaki
Although the classic coverage of pension research is frequently concerned with long-run analyses and forecasts of the system's viability, there are fewer longitudinal studies made of past and future generations despite their specific interest. The main purpose of this paper is to examine the extent to which pension systems maintain intertemporal justice, taking equal account of the interests of the individuals regardless of their date of birth; if the system is always run on the basis of uniformity, reciprocity and equality over time. Public opinion is concerned about the assets used and the people who will never recoup the sum they have contributed and who distrust this "contract between generations". It remains to be seen the extent to which this reaction is justified.Le système de retraite et l'équité intergênérationnelle
par Alexandra Tragaki
Si le champ traditionnel de la recherche concernant la retraite s'intéresse fréquemment aux diagnostics et projections à long terme sur la viabilité du système, les travaux longitudinaux consacrés aux bilans des générations passées et futures demeurent, malgré leur intérêt particulier, moins nombreux. L'intérêt principal de cet article est d'examiner jusqu'à quel point les systèmes de retraite préservent la justice intertemporelle en prenant soin égal des intérêts des gens quelle que soit leur date de naissance ; autrement dit si le système fonctionne toujours sur l'uniformité, la réciprocité, l'égalité au cours du temps. L'opinion publique parle des actifs exploités, des gens qui n'arriveront jamais à récupérer la somme qu'ils auront cotisée et qui doutent de ce "contrat entre les générations". Il reste à vérifier jusqu'à quel point cette réaction est justifiée.Tragaki Alexandra. Le système de retraite et l'équité intergénérationnelle. In: Économie & prévision, n°136, 1998-5. pp. 107-116
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
Sous le peplos d’Athéna
No full textDepuis la contribution de Nicole Loraux à l’Histoire des femmes en Occident, dans laquelle elle posait la question « Qu’est-ce qu’une déesse ? », réfléchir sur le genre d’une divinité n’est plus une incongruité. Et s’il en est bien une pour laquelle la question mérite d’être posée, c’est assurément Athéna. Du reste, on n’a pas manqué de le faire, au moins implicitement, comme le relèvent Susan Deacy et Claudia Alexandra Villing dans la mise en perspective historiographique des études sur la d..
D'un écho à un imprésenté : Resurrecting the Sublime de Alexandra Daisy Ginsberg
No full textInternational audienceDepuis sa thèse et sa principale publication, Alexandra Daisy Ginsberg consacre ses recherches et ses projets au développement d’un design critique et spéculatif, à la croisée des sciences naturelles et de l’art. Accompagnée par des scientifiques, ingénieurs, historiens et spécialistes des sciences sociales, elle s’attache surtout à discuter des enjeux de la biologie synthétique et, précisons-le, son objectif n’est pas celui d’un positivisme de la science et de la technique qui conférerait une position démiurgique de l’humain sur le monde, mais d’une mise en évidence des relations qui composent le réel. En 2019, lors de la Biennale Internationale Design Saint-Étienne, elle présente Resurrecting the Sublime, une installation qui, à travers un ensemble de dispositifs techniques, amène le visiteur à s’interroger sur les rapports entre le réel comme condition de l’éprouvé et ce dont il fait l’expérience. Entendu que l’œuvre n’est jamais « la pleine présence » de la chose perçue mais un écho du réel, l’imagination du visiteur complète le réel. Cependant, dans l’intention de pouvoir s’affranchir du point de vue humain, Alexandra Daisy Ginsberg renverse la position du visiteur-sujet à celle d’objet constitutif de l’installation, s’attachant ainsi à mettre en exercice une désujettisation de l’expérience esthétique. Plus encore, par l’invocation du sublime, sentiment de l’incommensurable qui, selon Jean-François Lyotard se manifeste en dehors de la raison et des liens communément admis entre le sujet et l’objet, elle s’affranchit de la centralité du sujet. Nous faisons alors l’hypothèse que le sublime, cet « imprésenté » et cet « état de l’esprit sans esprit », sortirait le spectateur du corrélationisme même s’il lui est impossible de mesurer ce qui reste de cette expérience impensable puisque chercher à le faire, le ramènerait indéniablement au champ de la conscience
Gender Regimes and Welfare States in France: A historical perspective
No full textThis paper has a twofold aim. First, we will analyze the system of family benefits in relation with the income tax system in France through the adoption of a historical and gender perspective. While typologies of welfare states frequently neglect taxation, in our view, one must take family taxation into account because it provides incentives and disincentives for paid income. Moreover, in the case of France, a close relationship exists between family benefits and taxation on income, one that stems from certain discussions—discussions led to the birth of the French system.Second, we will demonstrate how and to what extent France has moved away from the male-breadwinner model. However, any decline of the malebreadwinner model does not, in turn, indicate a corresponding shift toward a dual caregiver model. Indeed, the current French model has ambiguous effects on gender relations.gender regimes, gender relations, unpaid work, French policy reform
Histoire de l'Irlande. De 1912 à nos jours
No full textInternational audienceLe lundi de Pâques 1916, une troupe d'insurgés part à l'assaut de la Grande Poste de Dublin et proclame l'Irlande indépendante. Les Britanniques mobilisent 6000 soldats. À la fin de la semaine, l'insurrection a fait plus de 500 morts et 2500 blessés. Du projet de Home Rule de 1912, promettant aux Irlandais une autonomie au sein du Royaume-Uni, aux négociations sur le Brexit, de sa genèse révolutionnaire jusqu'à la crise sanitaire, Alexandra Maclennan raconte la destinée singulière de la République d'Irlande. Elle revient sur la formation de son paysage politique, les origines et l'apaisement du conflit nord-irlandais, les scandales institutionnels qui ont ébranlé l'autorité de l'État et de l'Église, les mécanismes d'une prospérité aussi impressionnante que l'austérité qui s'en est suivie, pour conclure sur les toutes récentes révolutions sociétales. Que reste-t-il de cette singularité irlandaise qui vaut au pays l'affection du monde entier
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