The escape fraction of ionizing photons during the Epoch of Reionization:Observability with the Square Kilometre Array

One of the most important parameters in characterizing the Epoch of Reionization, the escape fraction of ionizing photons, fesc, remains unconstrained both observationally and theoretically. With recent work highlighting the impact of galaxy-scale feedback on the instantaneous value of fesc, it is important to develop a model in which reionization is self-consistently coupled to galaxy evolution. In this work, we present such a model and explore how physically motivated functional forms of fesc affect the evolution of ionized hydrogen within the intergalactic medium. Using the 21 cm power spectrum evolution, we investigate the likelihood of observationally distinguishing between a constant fesc and other models that depend upon different forms of galaxy feedback. We find that changing the underlying connection between fesc and galaxy feedback drastically alters the large-scale 21 cm power. The upcoming Square Kilometre Array Low Frequency instrument possesses the sensitivity to differentiate between our models at a fixed optical depth, requiring only 200 h of integration time focused on redshifts z = 7.5-8.5. Generalizing these results to account for a varying optical depth will require multiple 800 h observations spanning redshifts z = 7-10. This presents an exciting opportunity to observationally constrain one of the most elusive parameters during the Epoch of Reionization

A Corpus Based Analysis of Noun Modification in Empirical Research Articles in Applied Linguistics

Previous research has established the importance of the nouns and noun modification in academic writing because of their commonness and complexity. However, little is known about how noun modification varies across the rhetorical sections of research articles. Such a perspective is important because it reflects the interplay between communicative function and linguistic form. This study used a corpus of empirical research articles from the fields of applied linguistics and language teaching to explore the connection between article sections (Introduction, Methods, Results, Discussion; IMRD) and six types of noun modification: relative clauses, ing-clause postmodifiers, ed-clause postmodifiers, prepositional postmodifiers, premodifying nouns, and attributive adjectives. First the frequency of these six types of noun modification was compared across IMRD sections. Second, the study also used a hand coded analysis of the structure and structural patterns of a sample of noun phrases through IMRD sections. The results of the analyses showed that noun modification is not uniform across IMRD sections. Significant differences were found in the rates of use for attributive adjectives, premodifying nouns, and prepositional phrase postmodifiers. There were no significant differences between sections for relative clauses, ing-clause postmodifiers, or ed-clause postmodifiers. The differences between sections for attributive adjectives, premodifying nouns, and prepositional phrases illustrate the way the functions of these structures intersects with the functions of IMRD sections. For example, Methods sections describe research methods, which often have premodifying nouns (corpus analysis, conversation analysis, speech sample, etc.); this function of Methods sections results in a higher use of premodifying nouns compared to other sections. Results for structures of noun phrase across IMRD sections showed that the common noun modification patterns, such as premodifying noun only or attributive adjective with prepositional phrase postmodifier, were mostly consistent across sections. Noun phrase structures including pre-/post- or no modification did have differences across sections, with Introduction sections the most frequently modified and Methods sections the least frequently modified. The different functions of IMRD sections call for different rates of usage for noun modification, and the results reflected this. The results of this research benefit teachers of graduate students of applied linguistics in students\u27 research reading and writing by describing the use of noun modification in the sections of empirical research articles and aiding teachers in the design of materials to clarify the use of noun modification in these IMRD sections

Escalades dans les Alpes 1860-1869 d’Edward Whymper, une oeuvre à la croisée de l’art et de la science

Mémoire du Master 1 Cultures de l\u27écrit et de l\u27image portant sur le récit d’Edward Whymper, "Escalades dans les Alpes 1860-1869"

Astraeus - III. The environment and physical properties of reionization sources

In this work, we use the {\sc astraeus} (seminumerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dArk mattEr simUlationS) framework which couples galaxy formation and reionization in the first billion years. Exploring a number of models for reionization feedback and the escape fraction of ionizing radiation from the galactic environment ($f_\mathrm{esc}$), we quantify how the contribution of star-forming galaxies {(with halo masses $M_h>10^{8.2}$M$_\odot$)} to reionization depends on the radiative feedback model, $f_\mathrm{esc}$, and the environmental over-density. Our key findings are: (i) for constant $f_\mathrm{esc}$ models, intermediate-mass galaxies (with halo masses of $M_h\simeq10^{9-11}$M$_\odot$ and absolute UV magnitudes of $M_{UV} \sim -15$ to $-20$) in intermediate-density regions drive reionization; (ii) scenarios where $f_\mathrm{esc}$ increases with decreasing halo mass shift the galaxy population driving reionization to lower-mass galaxies ($M_h\lesssim10^{9.5}$M$_\odot$) with lower luminosities ($M_{UV} \gtrsim-16$) and over-densities; (iii) reionization imprints its topology on the ionizing emissivity of low-mass galaxies ($M_h\lesssim10^{9}$M$_\odot$) through radiative feedback. Low-mass galaxies experience a stronger suppression of star formation by radiative feedback and show lower ionizing emissivities in over-dense regions; (iv) a change in $f_\mathrm{esc}$ with galaxy properties has the largest impact on the sources of reionization and their detectability, with the radiative feedback strength and environmental over-density playing a sub-dominant role; (v) JWST-surveys (with a limiting magnitude of $M_{UV} = -16$) will be able to detect the galaxies providing $\sim 60-70\%$ ($\sim 10\%$) of reionization photons at $z=7$ for constant $f_\mathrm{esc}$ models (scenarios where $f_\mathrm{esc}$ increases with decreasing halo mass).Comment: 14 pages, 13 figures, accepted for publication in MNRA

Escalades dans les Alpes 1860-1869 d’Edward Whymper, une oeuvre à la croisée de l’art et de la science - Annexes

Annexes du mémoire du Master 1 Cultures de l\u27écrit et de l\u27image portant sur le récit d’Edward Whymper, "Escalades dans les Alpes 1860-1869"

Documentaires de Jean-Paul Janssen, esthétique et médiatisation de l’escalade de Patrick Edlinger (Les)

Mémoire du Master 2 Cultures de l\u27écrit et de l\u27image portant sur documentaires de Jean-Paul Janssen, esthétique et médiatisation de l’escalade de Patrick Edlinger

Astraeus VIII: A new framework for Lyman-α\alpha emitters applied to different reionisation scenarios

We use the {\sc astraeus} framework to investigate how the visibility and spatial distribution of Lyman-$\alpha$ (Ly$\alpha$) emitters (LAEs) during reionisation is sensitive to a halo mass-dependent fraction of ionising radiation escaping from the galactic environment ($f_\mathrm{esc}$) and the ionisation topology. To this end, we consider the two physically plausible bracketing scenarios of $f_\mathrm{esc}$ increasing and decreasing with rising halo mass. We derive the corresponding observed Ly$\alpha$ luminosities of galaxies for three different analytic Ly$\alpha$ line profiles and associated Ly$\alpha$ escape fraction ($f_\mathrm{esc}^\mathrm{Ly\alpha}$) models: importantly, we introduce two novel analytic Ly$\alpha$ line profile models that describe the surrounding interstellar medium (ISM) as dusty gas clumps. They are based on parameterising results from radiative transfer simulations, with one of them relating $f_\mathrm{esc}^\mathrm{Ly\alpha}$ to $f_\mathrm{esc}$ by assuming the ISM of being interspersed with low-density tunnels. Our key findings are: (i) for dusty gas clumps, the Ly$\alpha$ line profile develops from a central to double peak profile as a galaxy's halo mass increases; (ii) LAEs are galaxies with $M_h\gtrsim10^{10}M_\odot$ located in overdense and highly ionised regions; (iii) for this reason, the spatial distribution of LAEs is primarily sensitive to the global ionisation fraction and only weakly in second-order to the ionisation topology or a halo mass-dependent $f_\mathrm{esc}$; (iv) furthermore, as the observed Ly$\alpha$ luminosity functions reflect the Ly$\alpha$ emission from more massive galaxies, there is a degeneracy between the $f_\mathrm{esc}$-dependent intrinsic Ly$\alpha$ luminosity and the Ly$\alpha$ attenuation by dust in the ISM if $f_\mathrm{esc}$ does not exceed $\sim50\%$.Comment: 25 pages, 9 figures; accepted for publication in MNRA

Astraeus VII: The environmental-dependent assembly of galaxies in the Epoch of Reionization

Using the ASTRAEUS (semi-numerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dark matter simUlationS) framework, we explore the impact of environmental density and radiative feedback on the assembly of galaxies and their host halos during the Epoch of Reionization. The ASTRAEUS framework allows us to study the evolution of galaxies with masses ($\rm 10^{8.2}M_\odot < M_{\rm h} < 10^{13}M_\odot$) in wide variety of environment ($-0.5 < {\rm log}(1+\delta) < 1.3$ averaged over $(2~{\rm cMpc})^3$). We find that : (i) there exists a mass- and redshift- dependent "characteristic" environment (${\rm log} (1+\delta_a(M_{\rm h}, z)) = 0.021\times M_{\rm h}^{0.16} + 0.07 z -1.12$, up to $z\sim 10$) at which galaxies are most efficient at accreting dark matter, e.g at a rate of $0.2\%$ of their mass every Myr at $z=5$; (ii) the number of minor and major mergers and their contributions to the dark matter assembly increases with halo mass at all redshifts and is mostly independent of the environment; (iii) at $z=5$ minor mergers contribute slightly more (by up to $\sim 10\%$) to the dark matter assembly while for the stellar assembly, major mergers dominate the contribution from minor mergers for $M_{\rm h}\lesssim 10^{11.5}M_\odot$ galaxies; (iv) radiative feedback quenches star formation more in low-mass galaxies ($M_{\rm h} \lesssim 10^{9.5}M_\odot$) in over-dense environments (${\rm log}(1+\delta) > 0.5$); dominated by their major branch, this yields star formation histories biased towards older ages with a slower redshift evolution.Comment: 17 pages, 15 figures, submitted to MNRAS, comments welcome