Buoyancy Instabilities in Galaxy Clusters: Convection Due to Adiabatic Cosmic Rays and Anisotropic Thermal Conduction

Using a linear stability analysis and two and three-dimensional nonlinear simulations, we study the physics of buoyancy instabilities in a combined thermal and relativistic (cosmic ray) plasma, motivated by the application to clusters of galaxies. We argue that cosmic ray diffusion is likely to be slow compared to the buoyancy time on large length scales, so that cosmic rays are effectively adiabatic. If the cosmic ray pressure $p_{cr}$ is $\gtrsim 25$ of the thermal pressure, and the cosmic ray entropy ($p_{\rm cr}/\rho^{4/3}$; $\rho$ is the thermal plasma density) decreases outwards, cosmic rays drive an adiabatic convective instability analogous to Schwarzschild convection in stars. Global simulations of galaxy cluster cores show that this instability saturates by reducing the cosmic ray entropy gradient and driving efficient convection and turbulent mixing. At larger radii in cluster cores, the thermal plasma is unstable to the heat flux-driven buoyancy instability (HBI), a convective instability generated by anisotropic thermal conduction and a background conductive heat flux. Cosmic-ray driven convection and the HBI may contribute to redistributing metals produced by Type 1a supernovae in clusters. Our calculations demonstrate that adiabatic simulations of galaxy clusters can artificially suppress the mixing of thermal and relativistic plasma; anisotropic thermal conduction allows more efficient mixing, which may contribute to cosmic rays being distributed throughout the cluster volume.Comment: submitted to ApJ; 15 pages and 12 figures; abstract shortened to < 24 lines; for high resolution movies see http://astro.berkeley.edu/~psharma/clustermovie.htm

Food geographies I: relational foodscapes and the busy-ness of being more-than-food

The study of foodscapes has spread throughout geography at the same time as food scholarship has spearheaded post-disciplinary research. This report argues that geographers have taken to post-disciplinarity to explore the ways that food is ‘more-than-food’ through analyses of the visceral nature of eating and politics and the vital (re)materializations of food’s cultural geographies. Visceral food geographies illuminate what I call the ‘contingent relationalities’ of food in the critical evaluation of the indeterminate, situated politics of ‘feeling food’ and those of the embodied collectivities of obesity. Questions remain, however, about how a visceral framework might be deployed for broader critiques within foodscapes and the study of human geography. The study of food’s vital materialisms opens up investigation into the practices of the ‘makings’ of meat, food waste and eating networks. Analysis of affect, embodiment and cultural practices is central to these theorizations and suggests consideration of the multiple materialisms of food, space and eating. There is, I contend, in the more radical, ‘post-relational’ approaches to food, the need for a note of caution. Exuberant claims for the ontological, vital agency of food should be tempered by, or at least run parallel to, critical questions of the real politik of political and practical agency in light of recent struggles over austerity, food poverty and food justice

Intensity Mapping of Lyman-alpha Emission During the Epoch of Reionization

We calculate the absolute intensity and anisotropies of the Lyman-alpha radiation field present during the epoch of reionization. We consider emission from both galaxies and the intergalactic medium (IGM) and take into account the main contributions to the production of Lyman-alpha photons: recombinations, collisions, continuum emission from galaxies and scattering of Lyman-n photons in the IGM. We find that the emission from individual galaxies dominates over the IGM with a total Lyman-alpha intensity (times frequency) of about (1.43-3.57)x10^{-8} erg s^{-1} cm^{-2} sr^{-1} at a redshift of 7. This intensity level is low so it is unlikely that the Lyman-\alpha background during reionization can be established by an experiment aiming at an absolute background light measurement. Instead we consider Lyman-\alpha intensity mapping with the aim of measuring the anisotropy power spectrum which has rms fluctuations at the level of 1 x 10^{-16} [erg s^[-1} cm^{-2} sr^{-1}]^2 at a few Mpc scales. These anisotropies could be measured with a spectrometer at near-IR wavelengths from 0.9 to 1.4 \mu m with fields in the order of 0.5 to 1 sq. degrees. We recommend that existing ground-based programs using narrow band filters also pursue intensity fluctuations to study statistics on the spatial distribution of faint Lyman-\alpha emitters. We also discuss the cross-correlation signal with 21 cm experiments that probe HI in the IGM during reionization. A dedicated sub-orbital or space-based Lyman-\alpha intensity mapping experiment could provide a viable complimentary approach to probe reionization, when compared to 21 cm experiments, and is likely within experimental reach.Comment: 18 pages, 17 figure

Percentage of High Schoolers\u27 with Daily Soda Consumption by State Compared to the Percentage of High Schoolers with Obesity by State

We will be presenting a poster on the percentage of high schoolers\u27 with daily soda consumption by state compared to the percentage of high schoolers with obesity by state

Biosocial “Science Talk”: Using Informal Interactive Programs to Help Children Explore the Human Body’s Relationship with the World Around It

This paper describes the application of a "biosocial" approach to informal health and science education. As an engagement between biological and critical social sciences, biosocial theory has sought to re-articulate human bodies as fundamentally the product of interrelationships between the biological and social dimensions of human life. Applying this approach to health and science education, we conducted approximately 200 public demonstrations at a science museum with school-aged participants over a two-year period. These demonstrations were designed to describe cutting edge research into "biosocial mechanisms" such as allostatic load and epigenetics. We examined survey responses and informal conversation with participants in order to characterize key themes that emerged within these interactions. Our analysis identifies a distinct biosocial "science talk" characterized, at varying degrees of complexity, by an emphasis on complex inter-relationships between environments and biology, the mutability of bodies, and the role of social structures and personal experiences in shaping health outcomes. We argue that these forms of science talk reflect the highly individualized and relational functioning of the biosocial mechanisms. We contend that this approach is not only accessible and easily adaptable to informal science education, but of increasing relevance given the impact of the COVID-19 pandemic.Temple University. College of Liberal ArtsGeography and Urban Studie

MIUSCAT: extended MILES spectral coverage. II. Constraints from optical photometry

In the present work we show a comprehensive comparison of our new stellar population synthesis MIUSCAT models with photometric data of globular clusters and early-type galaxies. The models compare remarkably well with the colours of Milky Way globular clusters in the optical range. Likewise, the colours of M31 globular clusters can also be explained by the models by assuming younger ages then their Galactic counterparts. When compared with quiescent galaxies we reproduce the colour evolution at intermediate redshift. On the other hand we find that the colour relations of nearby early-type galaxies are still a challenge for present-day stellar population synthesis models. We investigate a number of possible explanations and establish the importance of alpha-enhanced models to bring down the discrepancy with observations.Comment: 20 pages, 17 figures; MNRAS in press. Model predictions available at our website: http://miles.iac.e

MIUSCAT: extended MILES spectral coverage. I. Stellar populations synthesis models

We extend the spectral range of our stellar population synthesis models based on the MILES and CaT empirical stellar spectral libraries. For this purpose we combine these two libraries with the Indo-U.S. to construct composite stellar spectra to feed our models. The spectral energy distributions (SEDs) computed with these models and the originally published models are combined to construct composite SEDs for single-age, single-metallicity stellar populations (SSPs) covering the range 3465 - 9469\AA at moderately high, and uniform, resolution (FWHM=2.51\AA). The colours derived from these SSP SEDs provide good fits to Galactic globular cluster data. We find that the colours involving redder filters are very sensitive to the IMF, as well as a number of features and molecular bands throughout the spectra. To illustrate the potential use of these models we focus on the NaI doublet at 8200 \AA and with the aid of the newly synthesized SSP model SEDs we define a new IMF-sensitive index that is based on this feature, which overcomes various limitations from previous index definitions for low velocity dispersion stellar systems. We propose an index-index diagram based on this feature and the neighboring CaII triplet at 8600 \AA, to constrain the IMF if the age and [Na/Fe] abundance are known. Finally we also show a survey-oriented spectrophotometric application which evidences the accurate flux calibration of these models for carrying out reliable spectral fitting techniques. These models are available through our user-friendly website.Comment: 16 pages, 17 figures, 2 tables; MNRAS in press. Model predictions available at our website: http://miles.iac.e

The merger that led to the formation of the Milky Way's inner stellar halo and thick disk

The assembly process of our Galaxy can be retrieved using the motions and chemistry of individual stars. Chemo-dynamical studies of the nearby halo have long hinted at the presence of multiple components such as streams, clumps, duality and correlations between the stars' chemical abundances and orbital parameters. More recently, the analysis of two large stellar surveys have revealed the presence of a well-populated chemical elemental abundance sequence, of two distinct sequences in the colour-magnitude diagram, and of a prominent slightly retrograde kinematic structure all in the nearby halo, which may trace an important accretion event experienced by the Galaxy. Here report an analysis of the kinematics, chemistry, age and spatial distribution of stars in a relatively large volume around the Sun that are mainly linked to two major Galactic components, the thick disk and the stellar halo. We demonstrate that the inner halo is dominated by debris from an object which at infall was slightly more massive than the Small Magellanic Cloud, and which we refer to as Gaia-Enceladus. The stars originating in Gaia-Enceladus cover nearly the full sky, their motions reveal the presence of streams and slightly retrograde and elongated trajectories. Hundreds of RR Lyrae stars and thirteen globular clusters following a consistent age-metallicity relation can be associated to Gaia-Enceladus on the basis of their orbits. With an estimated 4:1 mass-ratio, the merger with Gaia-Enceladus must have led to the dynamical heating of the precursor of the Galactic thick disk and therefore contributed to the formation of this component approximately 10 Gyr ago. These findings are in line with simulations of galaxy formation, which predict that the inner stellar halo should be dominated by debris from just a few massive progenitors.Comment: 19 pages, 8 figures. Published in Nature in the issue of Nov. 1st, 2018. This is the authors' version before final edit

The biological, biographical, and biospheric dimensions of puberty onset: Using Bio3Science to frame transdisciplinary health research on puberty

This paper uses the case of puberty to characterize a new health science framework called Bio3Science and to provide an example of how trending research on biosocial mechanisms can be put to use to bridge siloed disciplines as well as the translational gap. Examined as an intricate, open-ended problem of scientific understanding, puberty offers a window to examine how three dimensions of human life – biology, biography, and biosphere – can be understood to shape human health and disease. Methods: Using the Bio3Science framework, a biosocial model of puberty was developed and critiqued by an interdisciplinary group of health science and social science researchers in a design studio setting. Results: The design and critique process resulted in a model and new conceptual framework that depicts puberty as a highly variable life experience that integrates multiple dense interactions and context-specific responses; within this model, the gene regulatory network (GRN) transformed from a biological to a biosocial mechanism, with conceptual and concrete applications. Conclusions: By providing a new, generalizable framework for understanding the integration of biology, biography, and biosphere in health research, opportunities emerge for more interdisciplinary work puberty, but also and more broadly, for more collaborative, inter-epistemological health research through the Bio3Science framework.Temple University. College of Liberal ArtsTemple University. College of Science and TechnologyGeography and Urban StudiesBiolog

Radical, Reformist, and Garden-Variety Neoliberal: Coming to Terms with Urban Agriculture’s Contradictions

For many activists and scholars, urban agriculture in the Global North has become synonymous with sustainable food systems, standing in opposition to the dominant industrial agri-food system. At the same time, critical social scientists increasingly argue that urban agriculture programmes, by filling the void left by the rolling back of the social safety net, underwrite neoliberalisation. I argue that such contradictions are central to urban agriculture. Drawing on existing literature and fieldwork in Oakland, CA, I explain how urban agriculture arises from a protective counter-movement, while at the same time entrenching the neoliberal organisation of contemporary urban political economies through its entanglement with multiple processes of neoliberalisation. By focusing on one function or the other, however, rather than understanding such contradictions as internal and inherent, we risk undermining urban agriculture\u27s transformative potential. Coming to terms with its internal contradictions can help activists, policy-makers and practitioners better position urban agriculture within coordinated efforts for structural change, one of many means to an end rather than an end unto itself