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An Exploration from Small Scales to Large Scales in Galaxy Simulations: Considering Open Cluster Chemistry and Bar Resonances in Galaxy Simulations
Get PDFOpen star clusters are the essential building blocks of the Galactic disk; “strong chemical tagging” – the premise that all star clusters can be reconstructed given chemistry information alone – is a driving force behind many current and upcoming large Galactic spectroscopic surveys. In this work, we characterize abundance patterns for 9 elements (C, N, O, Ne, Mg, Si, S, Ca, and Fe) in open clusters (OCs) in three galaxies (m12i, m12f, and m12m) from the \textit{Latte} suite of FIRE-2 simulations to investigate if strong chemical tagging is possible in these simulations. We select young massive () OCs formed in the last 100 Myr and calculate the intra- and inter-cluster abundance scatter for these clusters.We compare these results with analogous calculations drawn from observations of OCs in the Milky Way and find the intra-cluster scatter of the observations and simulations to be comparable. While the abundance scatter withineach cluster is minimal ( dex), the mean abundance patterns of different clusters are not unique. We also calculate the chemical difference in intra- and inter-cluster star pairs and find it, in general, to be so small that it is difficult to distinguish between stars drawn from the same OC or from different OCs. Despite tracing three distinct nucleosynthetic families (core-collapse supernovae, white dwarf supernovae, and stellar winds), we conclude that these elemental abundances do not provide enough discriminating information to use strong chemical tagging for reliable OC membership.Open clusters are relatively bright, easy to measure objects that are thought to be reliable tracers of the overall galactic radial metallicity gradient. Studies have shown that open clusters decrease in metallicity with increasing distance from the Galactic center; this distribution has often been modeled with a two-component linear fit, with a transition (knee), occurring between 10 and 16 kpc. Recent work from the APOGEE collaboration has significantly increased (> 150) the sample size of open clusters with robust measurements of chemistry across the Galactic disk.However, the susceptibility of this fit to the effects of sampling bias has been yet to be explored and could have large implications for the inferences drawn from the radial metallicity gradient. We selected young massive clusters less than 3 Myr old in our simulations and fit the radial metallicity gradient using the MCMC technique and find that sampling of open clusters significantly alters the observed trend of the fit parameters inner slope (m1), intercept (b), outer slope (m2) and knee (k). We performed bootstrapping of the fit to find that sampling can have an impact on the outer slope but significantly impacts the inner slope and the location of the knee. Using both bootstrapping and fixed sized random sub-samples of open clusters, we find that for reliable recovery of the fit parameters, we require at least 200-250 clusters spread across a wide range of galactocentric radii. With smaller or spatially biased samples, the fit parameters become highly sensitive to the sampling bias. It has been shown that more than 50\% of the disk galaxies, including our Milky Way galaxy, has a central bar with billions of stars clustered together. Theory suggests that galactic bars spin down throughout their evolution due to an angular momentum exchange with the inner parts of their dark matter halos. As opposed to a bar with a fixed pattern speed, Chiba et al. (2019) proposed that ‘resonance sweeping’ due to a decelerating galactic bar can explain local kinematic substructure in the solar neighborhood, like the Hercules stream. To date, resonance sweeping - a process of trapping and dragging the orbits of stars - has been explored both analytically and with test particle simulations that lack self-gravity. Here, we take such analyses a step further and examine resonance sweeping with a high resolution ( particles) self-consistent N-body simulation. We identify stars in Corotation Resonance and Outer Lindblad Resonance and find a significant number of stars remain in resonance later in time, suggesting resonant sweeping of orbits due to the decelerating bar. This result in a more realistic, self-gravitating disk indicates that the method of resonance sweeping can indeed be applied to Gaia data
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
The impact of the galactic environment on the dynamical evolution of long-lived open star clusters in the Latte suite of Feedback In Realistic Environment simulations
No full textOpen clusters serve as powerful tracers of the Milky Way's chemical and dynamical evolution. Because their member stars share common ages and chemical abundances, they provide insight into when and where stars formed in the Galactic disk, as well as how stars migrate and are dynamically heated over time. In this thesis, we use high-resolution cosmological zoom-in simulations from the FIRE-2 Latte suite (m12i, m12f, and m12m) to study the formation, evolution, and survivability of long-lived open clusters in realistic, Milky Way-like environments. We present a catalog of 128 gravitationally bound star clusters older than 1 Gyr that survive to present day (z=0). By tracking these clusters from their formation through cosmic time, we examine how local conditions, such as gas density, star formation environment, and proximity to giant molecular clouds, affect whether a cluster survives or is disrupted. We find that long-lived clusters tend to live in relatively low-density, kinematically quiet regions of the disk, and that these environments help shield clusters from disruption. Despite forming in dynamic disks that include spiral arms, gas flows, and satellite interactions, these clusters avoid disruption for billions of years. We also analyze the dynamical histories of these survivors to understand how processes like radial migration (both disk heating and cold torquing) shape their present-day orbits.
In the second part of the thesis, we focus on one extreme case study: a cluster nicknamed BOB, which serves as an analog to the old, metal-rich, and distant Milky Way open cluster Berkeley 20. This simulated cluster resides ~6 kpc from the galaxy's center and reaches vertical heights of several kiloparsecs. We trace the orbital and environmental history, identifying key perturbative episodes, including interactive with a gas cloud that prompts an outward migration event and a substantial interaction with an LMC mass satellite that causes significant orbit modification. This case study demonstrates how rare open clusters with unusual orbits may arise naturally as a consequence of the larger cosmological context. Together, this work provides a comprehensive view of the processes that govern open cluster survival and orbital evolution in realistic galactic environments
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From Quark Confinement to Dynamical History of Stars
Get PDFThis thesis includes two parts discussing two fascinating areas of fundamental physics. \textbf{Part (I)} explores the enigma of quark confinement within the intricate domain of quantum field theory, addressing a foundational puzzle in particle physics. Quark confinement dictates that quarks are bound within hadrons, so we cannot observe quarks as free, isolated particles. Despite extensive efforts over the past fifty years, the theoretical foundation of quark confinement in quantum chromodynamics (QCD) is still unclear. Studying the Schwinger effect (particle-antiparticle pair creation in vacuum in the presence of a strong external electromagnetic field) can pave the way to explore the behavior of quarks within hadrons. We utilize an indirect method, in particular the so-called AdS/QCD correspondence, to investigate the response of a QCD-like gauge theory to a static electromagnetic field. AdS/QCD correspondence is a form of gauge/gravity duality. This duality connects a gauge theory (representing particle physics) to a gravitational theory (specifically, string theory with an Anti-de Sitter background metric). Leveraging this method enables us to study the Schwinger effect for quark-antiquark pairs through potential analysis and calculation of the pair-production rate . Our findings show that both the potential analysis and the calculation of the pair-production rate yield consistent results. We identify two critical electric fields and as lower and upper bounds of a range in which pair production can occur only by tunneling through a potential barrier. Below , the potential barrier is insurmountable, and pair production cannot happen. Above , there is no potential barrier to restrict the pair production. While previous studies have explored various aspects of the Schwinger effect using AdS/QCD duality, further investigation is required for scenarios involving QCD-like gauge theories with simultaneous electric and magnetic fields. Addressing this research gap, our findings reveal that a magnetic field perpendicular to the electric field suppresses and increases . Conversely, a purely parallel magnetic field does not influence the system's response to an external electric field but enhances in the presence of a perpendicular magnetic field. \textbf{Part (II)} ventures into the cosmos, examining the formation of young stellar groups (both bound star clusters and unbound stellar associations) within a full cosmological context. A young stellar group is a collection of newly born stars moving together as a relatively coherent unit through a galaxy. Recent observational advancements, driven by improved precision of Gaia DR3, along with complementary near-field studies like PHANGS-HST and PHANGS-JWST, have significantly enhanced our understanding of stellar groups in the Milky Way and local universe galaxies, enabling us to study the conditions and environment that set clustered star formation across a statistically significant sample. Yet despite the exciting progress in observations, there is still a notable absence of robust theoretical cosmological models to interpret the data. Recent advancements in generating galaxy zoom-in simulations enable the comprehensive study of the formation and evolution of giant molecular clouds and stellar groups within a cosmological galactic framework and, in turn, facilitate filling the gap between observations and theoretical models. We present the fundamental properties of young massive stellar groups, both bound and unbound, formed within or near the galactic disk at the present time (at redshifts z < 0.008) in the \Latte suite of FIRE-2 Milky Way-like galaxy simulations. Our analysis encompasses the measurement of various characteristics for each stellar group, including its boundedness, mass, size (stellar group’s radius), 1D velocity dispersion, dispersion in age, and dispersion in metallicity [Fe/H]. We find the properties of simulated stellar groups with ages between 0 and 3 million years are within the range of values reported in observational studies. Our results depict the capability of \Latte simulations to generate reasonably realistic star clusters and associations and set the stage for the forthcoming project that will focus on generating synthetic images of the simulated stellar groups and measuring their properties by utilizing the conventional pipelines used in observational studies. This approach will allow a more consistent comparison between simulations and observations, aiding in the establishment of benchmarks for interpreting observations and advancing our understanding of various aspects of galaxy formation, such as stellar evolution, the impact of feedback on galactic dynamics, and the processes involved in star and planetary system formation
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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