310 research outputs found
Properties of massive Population III and metal-poor stars
No full textWe review the properties of massive Population III and very metal-poor stars, including briefly their formation, IMF, their main sequence evolution, possible mass loss mechanisms, atmosphere modeling etc. For detailed predictions concerning the properties of these stars we refer to Schaerer (2002) and Schaerer (2002) and references therein. Extending these calculations, Schaerer (2007) present new calculations concerning the ionizing power, Ly-α strength and related properties for different metallicities as well as for a range of power-law and log-normal IMFs. For illustrations from these studies see the Figures below. New detailed calibrations for solar metallicity O-type stars have recently been presented by Martins et al. (2005
Personal Papers (MS 80-0002)
No full textLetter from Ernest Schaerer to Mr. and Mrs. Kempner discussing potential hotel reservations at the Beau-Rivage-Palace, expressing their lack of the requested room and proposing alternatives
Transfert radiatif Lyman-alpha dans les galaxies
No full textPour étudier la formation et l'évolution des Galaxies, nous avons développé un code de transfert radiatif des photons Lyman-alpha à travers le milieu interstellaire d'une galaxie, MCLya. Emise par les atomes d'hydrogènes excités, cette raie de résonnance est altérée par les diffusions multiples qu'elle subit sur le gaz neutre et la poussière interstellaire. Cependant, elle est la seule information provenant des galaxies les plus lointaines observées. MCLya permet de modéliser les images et spectres Lyman-alpha observés, afin d'en déduire des contraintes sur la cinématique, la géométrie, la quantité de poussières du milieu interstellaire de ces galaxies. Ce travail a donné lieu à trois publications dans Astronomy&Astrophysics : une description détaillée du code (Verhamme et al. 2006), la modélisation d'un spectre en absorption pour valider la méthode (Schaerer%Verhamme 2008), et la caractérisation du milieu interstellaire de 11 galaxies en émission (Verhamme et al. 2008)
Systematische Ganzheitlichkeit : eine methodologische Vermittlung zwischen Perspektivität und Universalität
No full textZusammenfassung:
Diese Untersuchung ist das Ergebnis einer langjährigen Entwicklung, motiviert durch die Erfahrung von Widersprüchen und Zwängen in der internationalen beruflichen Praxis, die eine gründliche Auseinandersetzung mit den Möglichkeiten einer ganzheitlichen Erfassung von Situationen und Zusammenhängen nahe legten. Das Selbstverständnis von Philosophie hat sich dahin gehend entwickelt, Strukturen von Aussagen zu entwerfen und zu debattieren über Dinge und Zustände der Welt. Weil keine der daraus hervorgegangenen Positionen universelle Geltung beanspruchen kann, rivalisiert eine Unzahl von Versuchen, ohne daß eine wirklich ganzheitlich zielführend werden könnte. Im hier vorgelegten Ansatz ist die Grundidee, nicht wie üblich sofort über weltliche Dinge zu urteilen – was prinzipiell zu blinden Flecken und unvollständigen Welt¬bildern führen muß – sondern erst das Instrumentarium des Begrifflichen in seiner Eigendynamik kompromißlos auszuloten, durch welches jede Prädikation erfolgt. Für diese Klärung setzt der hier vorgeschlagene Ansatz beim Gesamtzusammenhang aller potentiellen Begrifflichkeit an, der die streng universell gültigen Ordnungen in der Wirklichkeit zugänglich macht und auch die Basis für die Grundgesetze der Logik bildet.
In der hier vorgelegten Darstellung der Zusammenhänge umfaßt das Vorwort die Bezüge zwischen subjektiver Erfahrung und objektiver Problematik (Kapitel 1). Das Anliegen als solches wird in der einführenden Diskussion diskutiert (Kapitel 2). Die Darstellung erfolgt in sieben Stufen bzw. Unterkapiteln: in 2.1 das Thema ergreifend, um die Basis für die Untersuchung zu legen; 2.2 die Probleme untersuchend zwischen rationalem Zugang und ganzheitlicher Erfassung, dadurch die Lösungsidee grob umreißend; 2.3 die Ursache von Behinderung im ganzheitlichen Erfassenwollen aufgreifend: 'Eingreifen statt Einfühlungsvermögen'; 2.4 die durch diese mentale Attitüde real erzeugte Selbstbegrenzungen auslotend; 2.5 die prinzipielle Vermeidbarkeit von solchen Grenzen erörternd, wie auch deren Auflösbarkeit; 2.6 eine naturgegebene inhalslogische Gesetzmäßigkeit aufspürend, welche im Begrifflichen erfüllt sein muß, wenn lückenlose Begreif¬barkeit erreichbar werden soll; 2.7 den Bezug zum Gesamtzusammenhang als Verbund aller Inhalte umreißend.
Dieser Denkpfad des reinen 'Horchens' kommt ohne jede Voraus-Setzung aus (es müssen aber bestimmte Vor-Bedingungen erfüllt sein); ihn beschreitend, wird die Qualität des vorgeschlagenen Lösungsansatzes – 'systematische Aufmerksamkeit' – allmählich erkennbar. Die ganzheitliche Auslotung der Eigengesetzlichkeit von perspektivischem Denken läßt eine Universalität erreichbar werden, die – im Gegensatz zu den üblichen philosophischen und wissenschaftlichen Methoden – allgemein die Brücke zwischen Perspektivität und Universalität zu schlagen erlaubt. Das Mittel dafür liegt in den grundbegrifflichen Strukturen, welche aus den rein logischen Implikationen eines Frage-Inhalts heraus entfaltet werden können und dann als kategoriale Ganzheit angewendet werden sollten. Die Methode im Vorgehen ist, den Inhalt einer Fragerichtung ganz auf sich selbst anzuwenden (vollständige Selbstbezüglichkeit – die in traditionellen Ansätzen begrenzt ist, aber in rein inhaltslogischem Vorgehen erreichbar). Es kommen die je entsprechenden rein inhaltlich bestimmten und streng polaren Grundbegrifflichkeiten zum Tragen, und das Ergebnis ist die je relevante Vierheit ('Tetrade') von konjugierten Kategorien. Es sind begriffliche Kontinua, welche heuristisch relevant und auf schlechthin alle Strukturen für die phänomenologische Erfassung anwendbar sind, nunmehr mit einer präzisen Ausrichtung. Deshalb bestehen im vorgeschlagenen Ansatz – als 'systematische Aufmerksamkeit' bezeichnet – keine disziplinären Grenzen; im Gegenteil erlaubt er eine prinzipiell unbegrenzte Inter- und Transdiziplinarität.
Um die streng allgemeine Anwendbarkeit dieses Ansatzes nachzuweisen, wird er in Kapitel 3 auf die Geowissenschaften angewandt. Diese Disziplin ist dafür besonders geeignet, weil sie in einem homogenen begrifflichen Instrumentarium die gesamte Spannweite vom Mineralischen über das Vegetabile und Sinnesorientierte bis zum Mentalen und Sozialen klar erfaßbar machen sollte. Just dies ist eine der Stärken des vorgeschlagenen Denkansatzes. Die Problematik wird im Unterkapitel 3.1 angegangen durch eine Erörterung der methodologischen Desiderate, dabei die Mathematik und Thermodynamik erörternd als eine Art von lingua franca zwischen heutigen wissenschaftlichen Disziplinen allgemein. Anschließend werden in Unterkapitel 3.2 die Bereiche in den Geowissenschaften kurz im Lichte der 'systematischen Aufmerksamkeit' beleuchtet: (1) physische Geographie als 'Speicher', 'Regler' und 'Prozeß', (2) Klimakunde / Meteorologie als 'Energie' und 'Information', (3) Bodenkunde als Verbindungsort von Anorganik und Organik, (4) Geoökologie mit den 'homogenen Einheiten' der naturräumlichen Gliederung, (5) Biogeographie mit den Biozönosen, Biotopen, und den Stufen des Organischen, (6) Humangeographie mit der Autonomie und Heteronomie des Menschen in seiner individuellen und sozialen Organisation, (7) theoretische Geowissenschaft als Ort der prinzipiellen Integration aller Seinsebenen. In Unterkapitel 3.3 wird noch kurz die Eigengesetzlichkeit der Einwirkung des Menschen auf die Natur umrissen.
Kapitel 4 versammelt kurze Kommentare zu den akkumulierten Publikationen. Nach Glossar und Literatur folgen in einem Quasi-Kapitel 5 die neun akkumulierten Publikationen selbst. Die Untersuchung als Ganze ist durchgehend paginiert.
----------
Summary:
In my professional life, partly in international planning and urban design, I experienced massive contradictions in the official line of thought, producing unnecessary conflict. Philosophy has developed a self-concept of devising and debating structures of statements and states of worldly affairs. Since no attempt of this sort can ever achieve a strictly complete grasp and universal validity, myriads of them are rivaling, but ultimately all have some flaw. This complex of problems motivated me to go back to university for meditating on integral ways of thinking. The presented investigation is the end result, now molded into a methodological system. The basic idea in the presented approach is not, as usual, to predicate immediately on worldly objects – which inevitably leads to blind spots and incomplete world-views – but to fathom first of all the instrumentation in the conceptual realm with its inherent self-dynamics that underlies all forms of predication. For achieving this objective, the proposed approach sets out on the characteristics of interconnectedness in all potential conceptuality, which allows the universally valid form of order securely to be approached that constitutes also the matrix for the fundamental laws of logic.
In the presented investigation, 'Vorwort' means Preface and covers as chapter 1 the relation between subjective authorship and objective questions as implied by the chosen topic. 'Einleitung' means Introduction and features as chapter 1 the issues that follow objectively from the discussed subject matter, namely integral ways of understanding and being, which determine therefore the approach and the method. This chapter offers also an overview over the structure of the problem and possible remedies, working through it in seven steps: in subchapter (2.1) taking hold of its meaning, its intrinsic content, (2.2) outlining a rational approach to this content, and discovering that problems in integral understanding are not imposed by nature, but man-made, (2.3) revealing how habitual approaches manifest – even in pure brain work – not empathy, but a powerful intervention, by setting out on basic assumptions, fundamental beliefs, (2.4) showing the actual results of such interventions, thereby disclosing the type of initiative that allows the problems to be dissolved, (2.5) actually possible procedures for avoiding on principle the occurrence of such discontinuities, (2.6) finding a law of content logic that determines the conceptual conditions for intelligibility and is at the root of the basic laws of formal logic, thereby warranting the general resolvability of the approached complex of problems, (2.7) outlining the bearings of the proposed approach (dubbed 'systematic attentiveness') in the overall interrelations, which the proposed approach allows to be viewed as an ordered complex.
The outlined procedure of pure 'listening' can do without any kind of presupposition (while certain preconditions must be fulfilled) and gradually makes intelligible the integral quality of the proposed approach. Fathoming perspectivity in this way fosters a universality that allows – in contrast to usual procedures in philosophy and science – the gap between the two aspects to be bridged. The means for this conciliation reside in the fundamental conceptual structures that can be unfolded out of the purely logical implications of any given query content and should then be applied as a categorial wholeness. The method in proceeding is to apply the given query content onto itself (complete self-referentiality – which is limited in traditional approaches, but attainable in pure content logic). The fundamental conceptual structures that follow in pure content logic from the chosen or given query content can then take effect, and the end result is the respective fourness ('tetrad') of conjugated categories. These constitute conceptual continua that are relevant on the heuristic level and applicable to all structures in phenomenological observation, now in a precise alignment. Due to this quality, the proposed approach – dubbed 'systematic attentiveness' – has no disciplinary limits; on the contrary it allows an inter- and trans-disciplinarity that is on principle unlimited.
For verifying the general applicability of 'systematic attentiveness', this approach is applied in chapter (3) to the geosciences because this discipline should cover the full scope from mineral existence to vegetal, sensory and mental life, up to social organization, including all interactions, in a conceptually homogenous way. Subchapter (3.1) contains some general considerations on the theoretical level, broaching the issue of mathematics as lingua franca in the sciences, as well as problems in interpreting thermodynamics, for indicating in (3.2) the applicability of the proposed approach in pivotal sub-disciplines of the geosciences: physical geography (with its categories of 'accumulator', 'regulator' and 'process'), climate studies ('energy' and 'information'), lithosphere (the locus of interlacing inert and alive structures), geoecology, biogeography, human geography, and purely theoretical geosciences, concluding (3.3) with issues of human action on nature.
Chapter (4) consists of brief comments to the accumulated articles that follow as such in the fifth and last part of this study. These nine publications reveal other aspects of applicability. They contain some redundancies due to a need of exposing my critique and approach again and again. Most of the papers are written in English, so for Anglophone readers they are self-explanatory
Realistic ionizing fluxes for young stellar populations from 0.05 to 2 ZÔ
No full textWe present a new grid of ionizing fluxes for O and Wolf–Rayet (W–R) stars for use with evolutionary synthesis codes and single-star H ii region analyses. A total of 230 expanding, non-LTE, line-blanketed model atmospheres have been calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 Z⊙) using the wm-basic code of Pauldrach, Hoffmann & Lennon for O stars and the cmfgen code of Hillier & Miller for W–R stars. The stellar wind parameters are scaled with metallicity for both O and W–R stars. We compare the ionizing fluxes of the new models with the CoStar models of Schaerer & de Koter and the pure helium W–R models of Schmutz, Leitherer & Gruenwald. We find significant differences, particularly above 54 eV, where the emergent flux is determined by the wind density as a function of metallicity. The new models have lower ionizing fluxes in the He i continuum with important implications for nebular line ratios. We incorporate the new models into the evolutionary synthesis code starburst99 and compare the ionizing outputs for an instantaneous burst and continuous star formation with the work of Schaerer & Vacca (SV98), and Leitherer et al. The changes in the output ionizing fluxes as a function of age are dramatic. We find that, in contrast to previous studies, nebular He ii λ4686 will be at, or just below, the detection limit in low metallicity starbursts during the W–R phase. The new models have lower fluxes in the He i continuum for Z≥ 0.4 Z⊙ and ages ≤7 Myr because of the increased line blanketing. We test the accuracy of the new model atmosphere grid by constructing photoionization models for simple H ii regions, and assessing the impact of the new ionizing fluxes on important nebular diagnostic line ratios. For the case of an H ii region where the ionizing flux is given by the WM-basic dwarf O star grid, we show that He iλ5786/Hβ decreases between 1 and 2 Z⊙ in a similar manner to observations. We find that this decline is caused by the increased effect of line blanketing above solar metallicity. We therefore suggest that a lowering of the upper mass limit at high abundances is not required to explain the diminishing strength of He iλ5786/Hβ , as has been suggested in the past. For an H ii region where the ionizing flux is provided by an instantaneous burst of total mass 106 M⊙ , we plot the softness parameter η' against the abundance indicator R23 for ages of 1–5 Myr. The new models are coincident with the observational data of Bresolin et al., particularly during the W–R phase, unlike the previous models of SV98 which generally over-predict the hardness of the ionizing radiation
New insight on the far-UV SED and He ii emission from low metallicity galaxies
No full textUnderstanding the ionizing spectrum of low-metallicity galaxies is of great importance for modeling and interpreting emission line observations of early/distant galaxies.
Although a wide suite of stellar evolution, atmosphere, population synthesis, and photoionization models, taking many physical processes into account now exist, all models face a common problem: the inability to explain the presence of nebular He ii emission, which is observed in many low metallicity galaxies, both in UV and optical spectra. Several possible explanations have been proposed in the literature, including Wolf-Rayet (WR) stars, binaries, very massive stars, X-ray sources, or shocks. However, none has so far been able to explain the major observations.
We briefly discuss the He ii problem, available empirical data, and observed trends combining X-ray, optical and other studies. We present a simple and consistent physical model showing that X-ray binaries could explain the long-standing nebular He ii problem. Our model, described in Schaerer et al. (2019), successfully explains the observed trends and strength of nebular He ii emission in large samples of low metallicity galaxies and in individual galaxies, which have been studied in detail and with multi-wavelength observations. Our results have in particular important implications for the interpretation of galaxy spectra in the early Universe, which will be obtained with upcoming and future facilities.</p
Physical properties of star-forming galaxies contributing to Cosmic Reionization
No full textThe reionization of the intergalactic medium (IGM) is the last major phase transition undergone by the Cosmos, and constitutes one of the few unexplored frontiers in observational cosmology. Although several evidences point to an ionizing photon background at these epochs dominated by star-forming galaxies (SFGs), little is known yet about the exact conditions that allowed Lyman Continuum (LyC) photons to escape from galaxies, as well as about the physical properties of the cosmic reionizers.
Following an observational approach, in this thesis, we have investigated the physics of LyC escape in an unprecedented, statistical way, based on Hubble Space Telescope observations from the Low Redshift Lyman Continuum Survey (LzLCS). Sources with high escape fraction of ionizing photons (fesc) are characterized by high, compact star-formation, a highly ionized interstellar medium (ISM) and prominent Lyman-alpha emission. The mechanisms of LyC leakage were studied by the analysis of down-the-barrel absorption transitions, features probing the cold, low-ionized gas in the ISM. The spectra of Lyman Continuum emitters (LCEs) show systematically weak absorption lines with non-zero residual fluxes, the latter tracing channels in the ISM with low-columm-density throughout LyC radiation escapes (originated after stellar winds or supernovae, presumably).
Using LzLCS data, we found that strong LCEs show low values of dust-attenuation and consequently steep, negative (blue) slopes in the ultraviolet continuum (beta-slope). In addition, we report a tight connection between beta-slope and the product of the escape fraction and the ionizing production efficiency. Integrating this relation over the number density of galaxies at the EoR shows that SFGs provided sufficient LyC photons to exceed recombinations at z = 7 - 8.
Finally, by invoking radiative transfer arguments, we provide empirical recipes to predict fesc from simple measurements of the absorption lines and dust-attenuation in galaxies. We apply this method for the first time to a sample of SFGs at 3 < z < 5 with deep, rest-ultraviolet spectra from the VANDELS ESO public spectroscopic survey. By extrapolating our conclusions to the EoR, our results suggests that the ionizing output at the EoR was most probably dominated by the low-mass and dustless galaxies which, according to recent observations from the James Webb Space Telescope, seem to be common properties in the high-z Universe. </p
Properties and star formation histories of high-z IR-detected galaxies with Herschel
No full textThe Herschel Space Observatory (ESA) has offered an unprecedented view of the far infrared (FIR) emission of the Universe, granting astronomers access over more than 10 billion years of galaxy evolution. Star formation and the closely related dust creation are two central aspects that led the Universe to its present state of diversity and chemical enrichment. They also set the rules for observing the Universe and Herschel has been crucial to complete our coverage of the electromagnetic spectrum. Using a wealth of ancillary observational data along the FIR, this thesis focuses on the multi-wavelength characterization of IR-detected star-forming galaxies of intermediate to high redshift (1 to 4) in the aftermath of the Herschel mission. It is composed of three main stages, the central purpose of which is to derive the physical properties and constrain the star formation histories (SFHs) of the studied galaxies, via the analysis of their spectral energy distribution
Les vicissitudes d'un outil cosmologique : la raie Lyman-α
No full textL'exploration de l'Univers lointain connaît présentement un essor sans précédent, grâce notamment à une instrumentation de pointe en perpétuelle amélioration. Les galaxies primordiales sont devenues accessibles par une signature spectrale très intense : la raie de recombinaison de l'hydrogène Lyα. En procède une pléthore d'applications cosmologiques, qui demeurent cependant très fragiles et en proie à diverses incertitudes. En cause, la complexité du transfert radiatif de Lyα, qui est une raie résonante. La présente thèse a pour principal objectif la calibration et la consolidation des quantités, observations et interprétations astrophysiques basées sur l'émission Lyα, en particulier dans l'univers lointain. L'approche principale consiste à observer les analogues locaux des galaxies a flambée de formation d'étoiles distantes, permettant une étude détaillée de la physique Lyα à haute résolution grâce au télescope spatial Hubble. Une étude numérique présente ensuite la simulation du transfert radiatif de Lyα dans les galaxies locales et à un décalage spectral de 3, et le lien entre différentes populations de galaxies. Enfin, la dernière partie de ce travail présente une estimation empirique d'une quantité physique cruciale pour la calibration des observables Lyα, à savoir la fraction d'échappement fesc(Lyα), ainsi que les caractéristiques physiques des émetteurs Lyα détectés par GALEX.The Lyα emission line is currently a leading tracer of star formation at cosmological distances. Since it becomes the strongest line in the optical-NIR window at redshift ≥ 2.1. Lyα proves an invaluable tool by which to detect galaxy populations at highest redshifts and a versatile mean for galaxy evolution diagnostics. However, with respect to these promising Lyα -based cosmological studies, number of inconsistencies have first to be understood to ensure proper interpretations. This is the main goal of the present work. Since typical high-z galaxies are very faint and detailed observations are difficult, we present an alternative approach which relies on observations of their local analogs using the Hubble space telescope to investigate the Lyα escape mechanisms. Then, we perform Lyα radiative transfer simulations in local and distant galaxies to understand the link between the different galaxy populations. Finally, we present the first empirical estimate of the Lyα escape fraction in a large sample of Lyα emitters in order to calibrate different Lyα -based cosmological quantities
Resolved Star-Formation Properties of Strongly Lensed Galaxies at Cosmic Noon
No full textThis thesis explores the secrets of galaxies during cosmic noon, a transformative epoch around redshift z=1-3 when star-formation activity within galaxies was at its peak. Leveraging gravitational lensing as a cosmic telescope, the study delves into the details of high-redshift galaxies and their star-formation characteristics at small spatial scales. Key questions addressed include the spatial distributions of critical galactic parameters (stellar mass, star formation rate, molecular gas mass, and dust mass) in distant galaxies, the manifestation of the Kennicutt Schmidt (KS) law at integrated and sub-kiloparsec scales in the early Universe, and the intrinsic properties of star-forming clumps and giant molecular clouds (GMCs) in high-redshift galaxies.Cette thèse explore les secrets des galaxies pendant le cosmic noon, une époque transformative autour du redshift z=1-3, lorsque l'activité de formation stellaire au sein des galaxies était à son apogée. En exploitant le phénomène de lentille gravitationnelle comme un télescope cosmique, l'étude plonge dans les détails des galaxies à haut redshift et de leurs caractéristiques de formation stellaire à petites échelles spatiales. Les questions clés abordées comprennent les distributions spatiales des paramètres galactiques critiques (masse stellaire, taux de formation stellaire, masse du gaz moléculaire et masse des poussières) dans les galaxies lointaines, la manifestation de la loi de Kennicutt-Schmidt (KS) à des échelles intégrées et sous-kiloparsec dans l'Univers primitif, et les propriétés intrinsèques des clumps de formation stellaire et des nuages moléculaires géants (GMC) dans les galaxies à haut redshift
- …
