Nonparametric star formation histories (SFHs) have long promised to be the "gold standard" for galaxy spectral energy distribution (SED) modeling as they are flexible enough to describe the full ...diversity of SFH shapes, whereas parametric models rule out a significant fraction of these shapes a priori. However, this flexibility is not fully constrained even with high-quality observations, making it critical to choose a well-motivated prior. Here, we use the SED-fitting code Prospector to explore the effect of different nonparametric priors by fitting SFHs to mock UV-IR photometry generated from a diverse set of input SFHs. First, we confirm that nonparametric SFHs recover input SFHs with less bias and return more accurate errors than do parametric SFHs. We further find that, while nonparametric SFHs robustly recover the overall shape of the input SFH, the primary determinant of the size and shape of the posterior star formation rate as a function of time (SFR(t)) is the choice of prior, rather than the photometric noise. As a practical demonstration, we fit the UV-IR photometry of ∼6000 galaxies from the Galaxy and Mass Assembly survey and measure scatters between priors to be 0.1 dex in mass, 0.8 dex in SFR100 Myr, and 0.2 dex in mass-weighted ages, with the bluest star-forming galaxies showing the most sensitivity. An important distinguishing characteristic for nonparametric models is the characteristic timescale for changes in SFR(t). This difference controls whether galaxies are assembled in bursts or in steady-state star formation, corresponding respectively to (feedback-dominated/accretion-dominated) models of galaxy formation and to (larger/smaller) confidence intervals derived from SED fitting. High-quality spectroscopy has the potential to further distinguish between these proposed models of SFR(t).
ABSTRACT This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar ...evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages ( ), masses ( ), and metallicities ( ). The models are self-consistently and continuously evolved from the pre-main sequence (PMS) to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the PMS to the end of core helium burning for . We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at http://waps.cfa.harvard.edu/MIST/.
The flora of southern Africa has exceptional species richness and endemism, making it an ideal system for studying the patterns and processes of evolutionary diversification. Using a wealth of recent ...case studies, I examine the evidence for pollinator-driven diversification in this flora. Pollination systems, which represent available niches for ecological diversification, are characterized in southern Africa by a high level of ecological and evolutionary specialization on the part of plants, and, in some cases, by pollinators as well. These systems are asymmetric, with entire plant guilds commonly specialized for a particular pollinator species or functional type, resulting in obvious convergent floral evolution among guild members. Identified modes of plant lineage diversification involving adaptation to pollinators in these guilds include (i) shifts between pollination systems, (ii) divergent use of the same pollinator, (iii) coevolution, (iv) trait tracking, and (v) floral mimicry of different model species. Microevolutionary studies confirm that pollinator shifts can be precipitated when a plant species encounters a novel pollinator fauna on its range margin, and macroevolutionary studies confirm frequent pollinator shifts associated with lineage diversification. As Darwin first noted, evolutionary specialization for particular pollinators, when resulting in ecological dependency, may increase the risk of plant extinction. I thus also consider the evidence that disturbance provokes pollination failure in some southern African plants with specialized pollination systems.
Because most plants rely on animals for pollination, insights from animal sensory ecology and behavior are essential for understanding the evolution of flowers. In this review, we compare and ...contrast three main types of pollinator responses to floral signals – receiver bias, ‘adaptive’ innate preferences, and associative learning – and discuss how they can shape selection on floral signals. We show that pollinator-mediated selection on floral signals can be strong and that the molecular bases of floral signal variation are often surprisingly simple. These new empirical and conceptual insights into pollinator-mediated evolution provide a framework for understanding patterns of both convergent (pollination syndromes) and advergent (floral mimicry) floral signal evolution.
•Acidic microbiomes are tractable model systems in biogeochemical cycling studies.•Their spatial diversity patterns have been resolved at several different scales.•The main physico-chemical drivers ...of their diversity patterns have been uncovered.•Advances anticipate new opportunities to synthetically engineer relevant interactions.
Extremely acidic environments have global distribution and can have natural or, increasingly, anthropogenic origins. Extreme acidophiles grow optimally at pH 3 or less, have multiple strategies for tolerating stresses that accompany high levels of acidity and are scattered in all three domains of the tree of life. Metagenomic studies have expanded knowledge of the diversity of extreme acidophile communities, their ecological networks and their metabolic potentials, both confirmed and inferred. High resolution compositional and functional profiling of these microbiomes have begun to reveal spatial diversity patterns at global, regional, local, zonal and micro-scales. Future integration of genomic and other meta-omic data will offer new opportunities to utilize acidic microbiomes and to engineer beneficial interactions within them in biotechnologies.
Black hole images present an annular region of enhanced brightness. In the absence of propagation effects, this "photon ring" has universal features that are completely governed by general relativity ...and independent of the details of the emission. Here, we show that the polarimetric image of a black hole also displays universal properties. In particular, the photon ring exhibits a self-similar pattern of polarization that encodes the black hole spin. We explore the corresponding universal polarimetric signatures of the photon ring on long interferometric baselines, and propose a method for measuring the black hole spin using a sparse interferometric array. These signatures could enable spin measurements of the supermassive black hole in M87, as well as precision tests of general relativity in the strong field regime, via a future extension of the Event Horizon Telescope to space.
The Canadian Light Source Bancroft, G. M; Johnson, D. D
The Canadian Light Source,
2020, 2020, 2020-08-10, 2020-08-26
eBook
"The creation of the Canadian Light Source in Saskatoon, which began operation in 2004, was the largest science project in Canada in the last fifty years. The multi-beam facility operates over five ...thousand hours per year for over one thousand Canadian and international users from a wide range of science, medical and engineering disciplines. This book describes the decades of intense research from many scientists to justify this project; the remarkable and unprecedented collaboration and cooperation of governments, universities, and industries across Canada; and the resulting outstanding research covering many areas of the physical, biological, medical, and agricultural sciences. With personal accounts and frank narration, this book describes the long history from 1934-2001 leading to the CLS, beginning in Saskatoon in the 1930s. The major part of the book details the remarkable and unselfish collaboration and cooperation of a few hundred people from Canadian and international universities, governments, and industry, showcasing how the Canadian Light Source represents pure and applied research at its finest."--
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