Radiative Transfer Modeling of Lyman Alpha Emitters. II. New Effects in Galaxy Clustering

We study the clustering properties of z~5.7 Lyman-alpha emitters (LAEs) in a cosmological reionization simulation with a full Lya radiative transfer calculation. Lya radiative transfer substantially modifies the intrinsic Lya emission properties, compared to observed ones, depending on the density and velocity structure environment around the Lya emitting galaxy. This environment-dependent Lya selection introduces new features in LAE clustering, suppressing (enhancing) the line-of-sight (transverse) density fluctuations and giving rise to scale-dependent galaxy bias. In real space, the contours of the three-dimensional two-point correlation function of LAEs appear to be prominently elongated along the line of sight on large scales, an effect that is opposite to and much stronger than the linear redshift-space distortion effect. The projected two-point correlation function is greatly enhanced in amplitude by a factor of up to a few, compared to the case without the environment dependent selection effect. The new features in LAE clustering can be understood with a simple, physically motivated model, where Lya selection depends on matter density, velocity, and their gradients. We discuss the implications and consequences of the effects on galaxy clustering from Lya selection in interpreting clustering measurements and in constraining cosmology and reionization from LAEs.Comment: 31 pages, 26 figures, revised according to the referee's comments, more discussions and tests, published in Ap

Radiation Effects in Apatite and High Entropy Alloy under Energetic Ions and Electrons

Radiation effects in apatite and high entropy alloy under energetic ions and electrons are studied in this doctoral dissertation to develop advanced crystalline ceramic waste forms and nuclear structural materials. Apatite is proposed as a ceramic waste form for the immobilization of radionuclides, but its performance is strongly affected by the irradiation of the incorporated radionuclides. It is thus important to understand the radiation effects in apatite structure and the underlying physics. Effects of chemical composition, grain size, interfacial structure, as well as radiation conditions on the microstructural evolution, phase transformation and damage mechanisms of apatite under alpha-decay and beta-decay events, simulated by 1 MeV Kr ions and 200 keV electrons respectively, are investigated. Composition effect on silicate apatite shows the better radiation tolerance under higher cerium content. Size effect on hydroxyapatite exhibits the reduction of radiation stability with the decrease of grain size due to excess surface energy in nanoparticles. A further study addresses densified nanocrystalline hydroxyapatite exhibits higher radiation tolerance than the same sized hydroxyapatite nanoparticle as a result of lower interface energy. Effect of radiation conditions on the recrystallization behaviors of pre-amorphized hydroxyapatite is also studied. In-situ TEM observation reveals a rapid recrystallization process and a notable size effect, which smaller sized sample nucleates and fully recrystallizes under lower electron fluence. Recrystallization mechanism is attributed to ionization process as a result of breaking and reforming of dangling bonds. The radiation effect study is further extended to include high entropy alloys intended as structural materials in advanced nuclear reactors. Two types of high entropy alloys are selected as model alloys to investigate the irradiation-induced behaviors under 1 MeV Krions. Study on nanocrystalline AlxCoCrFeNi alloys shows a notable ion-irradiation-induced grain growth, whose mechanisms are attributed to a disorder-driven mechanism for the initial fast increase of grain size and defect-stimulated mechanism for the later slow grain size increase, elucidated by the thermal spike model. Study on HfNbTaTiVZr alloy reveals a crystal-to-amorphous phase transformation with critical amorphization dose of 2 displacements per atom (dpa) at 298 K, while the amorphization is suppressed when the temperature increases to 423 K

Analysis and modeling of solar irradiance variations

A prominent manifestation of the solar dynamo is the 11-year activity cycle, evident in indicators of solar activity, including solar irradiance. Although a relationship between solar activity and the brightness of the Sun had long been suspected, it was only directly observed after regular satellite measurements became available with the launch of Nimbus-7 in 1978. The measurement of solar irradiance from space is accompanied by the development of models aimed at describing the apparent variability by the intensity excess/deficit effected by magnetic structures in the photosphere. The more sophisticated models, termed semi-empirical, rely on the intensity spectra of photospheric magnetic structures generated with radiative transfer codes from semi-empirical model atmospheres. An established example of such models is SATIRE-S (Spectral And Total Irradiance REconstruction for the Satellite era). One key limitation of current semi-empirical models is the fact that the radiant properties of network and faculae are not adequately represented due to the use of plane-parallel model atmospheres (as opposed to three-dimensional model atmospheres). This thesis is the compilation of four publications, detailing the results of investigations aimed at setting the groundwork necessary for the eventual introduction of three-dimensional atmospheres into SATIRE-S and a review of the current state of the measurement and modelling of solar irradiance. Also presented is an update of the SATIRE-S model. We generated a daily reconstruction of total and spectral solar irradiance, covering 1974 to the present, that is more reliable and, in most cases, extended than similar reconstructions from contemporary models.Comment: Doctoral thesis, ISBN 978-3-944072-07-

La caza de materia oscura en rayos-gamma con Fermi-LAT y CTA: modelado, predicciones y análisis en varios objetos astrofísicos

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de Lectura: 25-11-2022Gravitational evidences at diferent cosmological scales hint towards the existence of a dark component of the Universe, which amounts up to the 85% of its matter density. Despite all the eforts, the dark matter (DM) has eluded any clear detection and its ultimate nature remains still unknown. The current knowledge suggests that the DM cannot be identifed with the particles comprised in the Standard Model (SM). In this context, the Weakly Interacting Massive Particles (WIMPs) provide a framework that naturally yields the measured DM relic density, while at the same time they are expected to interact with SM particles. From these interactions, one of the most promising channels are γ-rays, which travel the Universe without defection, pointing back towards its original source. This Thesis has been devoted to unveil the unknown properties of the dark matter focusing on the so-called γ-ray indirect DM searches. We have conducted an exhaustive study of the DM contents and distribution in diferent interesting astrophysical objects and computed the state-of-the-art predictions for their annihilation and decay DM fuxes. Then, we have used these models to both, perform searches in existing F ermi-LAT data and obtain the prospects for the future Cherenkov Telescope Array (CTA). In the absence of detection, we proceed to a systematic search starting with galaxy clusters, known to be very good candidates to search DM emission. We compute the sensitivity to difuse γ-ray emission from Perseus, one of the most massive local galaxy clusters, of the future CTA, including in the analysis the CR-induced γ-rays as a background in a template ftting analysis. Staying with galaxy clusters, we then use 12 years of Fermi-LAT data from nearly 50 local galaxy clusters, searching for a DM-induced γ-ray signal, modelled including the expected substructures. We also explore introducing new targets in the quest of DM. For this, we perform the frst DM γ-ray search in dwarf irregular galaxies (dIrrs) using Fermi-LAT data. Finally, we collect the results of the previous studies to model the DM content of a subsample of objects that we have already investigated (dIrrs and clusters) and also of representative dark subhalos of the Milky Wa

The Universe at Ultraviolet Wavelengths: The first two years of International Ultraviolet Explorer

Highlights of the results obtained from the IUE satellite are addressed. specific topics discussed include the solar system, O-A stars, F-M stars, binary stars and highly evolved objects, nebulae and interstellar medium, and extragalactic objects. Data reduction techniques employed in the analysis of the varied data are also discussed

Listening to the Universe through Indirect Detection

Indirect detection is the search for the particle nature of dark matter with astrophysical probes. Manifestly, it exists right at the intersection of particle physics and astrophysics, and the discovery potential for dark matter can be greatly extended using insights from both disciplines. This thesis provides an exploration of this philosophy. On the one hand, I will show how astrophysical observations of dark matter, through its gravitational interaction, can be exploited to determine the most promising locations on the sky to observe a particle dark matter signal. On the other, I demonstrate that refined theoretical calculations of the expected dark matter interactions can be used disentangle signals from astrophysical backgrounds. Both of these approaches will be discussed in the context of general searches, but also applied to the case of an excess of photons observed at the center of the Milky Way. This galactic center excess represents both the challenges and joys of indirect detection. Initially thought to be a signal of annihilating dark matter at the center of our own galaxy, it now appears more likely to be associated with a population of millisecond pulsars. Yet these pulsars were completely unanticipated, and highlight that indirect detection can lead to many new insights about the universe, hopefully one day including the particle nature of dark matter.Comment: Ph.D. thesis, MIT, April 2018; based on the work appearing in arXiv:1708.09385, arXiv:1612.05638, arXiv:1612.04814, arXiv:1511.08787, arXiv:1503.01773, and arXiv:1402.670

Dusty Star Formation in Extreme Environments: Galaxies and Galaxy Clusters in the Distant Universe

In this thesis, we present a comprehensive study of the dust-obscured star formation (SF) activity in galaxy clusters out to high redshift using infrared (IR) imaging. Using hundreds of galaxy clusters and wide-field far-IR imaging across nine square degrees, we quantify the average star formation rates (SFRs) out to the distant Universe for mass-limited cluster galaxy samples using stacking. We compare the evolution of this SF activity to field galaxies, finding that the evolution in clusters occurs more rapidly than in the field and clusters have field-like SF approximately nine billion years ago, during an epoch before SF quenching becomes effective in massive clusters. Building on this result, we present new, deep far-IR imaging of 11 spectroscopically-confirmed clusters at high redshift, which allows us to examine the SFRs of individual IR-luminous cluster galaxies as a function of environment. We find a transition from field-like SF to quenching of IR-luminous galaxies in the cluster cores over the redshift range probed. We present the first UV-to-far-IR spectral energy distributions (SEDs) of high redshift cluster galaxies, quantify the cluster-to-cluster variations in SF properties, and compare cluster galaxies to star forming galaxies in the field. In addition, we examine the SEDs of cluster galaxies with measurable emission from black hole accretion and quantify the fraction of these galaxies as a function of environment and redshift, finding an excess at high redshift in the cluster cores. Lastly, we compare dust-obscured SFRs from far-IR to unobscured SFRs from optical emission lines. In the last section, we present new submillimeter imaging of a massive cluster in the distant Universe. We characterize the FIR/submillimeter SED of IR-luminous cluster galaxies, finding dust temperatures similar to that in field galaxies in the same epoch. We use imaging of dust emission in the optically thin regime to derive the interstellar medium (ISM) masses of cluster galaxies. Through this analysis, we determine that IR-luminous cluster galaxies at high redshift have comparable ISM masses, gas fractions, and gas depletion timescales as field galaxies

Morphologies and Dynamics in Low-Tg Single-Ion Conductors: Effects of Comonomers, Plasticizers, and Functionalized Nanoparticles

ABSTRACT MORPHOLOGIES AND DYNAMICS IN LOW-Tg SINGLE-ION CONDUCTORS: EFFECTS OF COMONOMERS, PLASTICIZERS, AND FUNCTIONALIZED NANOPARTICLES Michael V. O\u27Reilly Karen I. Winey Single-ion conducting polymers, or ionomers, are under extensive investigation for applications as solid electrolytes in battery applications. Slow segmental dynamics of viscous ionomers make them inadequately poor conductors. Faster segmental dynamics are attained by decreasing the glass transition temperature (Tg) of the ionomer. Three compositional avenues are presented to reduce the Tg of a PEO-based lithium conducting ionomer (Tg ~ -12 °C): copolymers, blends, and nanocomposites. A fourth study employs weak-binding salts and flexible siloxanes to achieve a low Tg ionomer. Random multiblock copolymers with PEO and PTMO segments spaced by lithium sulfonate groups between each block are employed reveal that the enhanced segmental dynamics provided by PTMO (Tg ~ -70 °C) are insufficient to offset the poor ion solvation ability caused by low ether oxygen content. Segmental dynamics of the PEO-based lithium conductor (without PTMO) can be enhanced by polymeric and nanoparticle plasticizers. PEG oligomeric plasticizer and silica nanoparticles functionalized with PEO are both capable of depressing the glass transition temperature of the ionomer. Consequently, accelerated ion dynamics are observed for both systems without salt or solvent additives. With functionalized nanoparticles, these findings are of particular interest since the nanoparticles are solid fillers while the PEG oligomeric plasticizer is liquid-like. As an alternative to plasticizing an ionomer with additives, single-ion conductors based on highly flexible siloxane backbones and low binding energy salts can demonstrate very low Tgs (Tg ~ -80 °C). The charge-delocalized nature of tetrabutylphosphonium salt prevents ionic aggregation and ionic conductivity is independent of ion content. By establishing these correlations between accelerated segmental dynamics and ionic conductivity, it will be possible to explore new chemistries that decouple the two properties in single-ion conductors