A Group of Red, Ly-alpha Emitting, High Redshift Galaxies

We have discovered two new high redshift (z=2.38) galaxies, near the previously known z=2.38 galaxy 2139-4434 B1 (Francis et al. 1996). All three galaxies are strong Ly-alpha emitters, and have much redder continuum colors (I-K about 5) than other optically-selected high redshift galaxies. We hypothesize that these three galaxies are QSO IIs; radio-quiet counterparts of high redshift radio galaxies, containing concealed QSO nuclei. The red colors are most easily modelled by an old (> 0.5 Gyr), massive (> 10E11 solar masses) stellar population. If true, this implies that at least one galaxy cluster of mass much greater than 3E11 solar masses had collapsed before redshift five.Comment: 12 pages, 2 figures, uses aaspp4 style file. Accepted for publication in Astrophysical Journal Letter

Revisiting the drivers of deforestation in the tropics: Insights from local and key informant perceptions in western Uganda

Deforestation has been widespread in the Northern Albertine Rift Landscape in rural Western Uganda. In this paper, we present perceptions from local residents and narratives from key informants on causes of forest loss during a 30-year period between 1985 and 2014. While the generic drivers we find are consistent with previous literature, we suggest that the specific context in which forest cover is lost in rural areas is path dependent, and this is vital for adequate management. In the Ugandan case, the history of the sugar industry and its relation to local political drivers and international considerations (e.g. biofuel) are prominent. Global drivers of forest loss therefore mask local-level complexities, but an amalgamation of local-level dynamics does not necessarily sum up to larger-scale manifestations (in a linear manner): striking a balance between understanding local-level and large-scale dynamics could be key in addressing the deforestation conundrum. We surveyed 263 households in 7 parishes around Budongo and Bugoma forests, and conducted 22 key informant interviews. Our findings indicate that the drivers and mechanisms of deforestation are local; they also vary between Budongo and Bugoma. Key amongst these include: agricultural expansion (28%–58.5% of the responses)—with large-scale commercial and small-scale subsistence farming significant around Budongo and Bugoma respectively; “poverty” (26%–76%) often alluding to heavy dependence on forests for livelihoods. Others include: population growth driven by dissimilar migratory patterns; and moving protected forest boundaries. Our data suggest that a combination of both local and key informant perceptions is instrumental in filling data gaps where a dearth of information is prevalent (especially around Bugoma forest), and is important for corroboration of other scientific data (e.g. remote sensing). However, a survey of wider literature indicates that there are significant issues missing from their stated views. While the continued expansion of cash-crop farming and lack of inclusion of local people in forest policy continues to raise concern, the stability of protected forest (i.e. Budongo and Bugoma) is encouraging and suggests a refocusing of the forest debate on practical working schemes for forest preservation and recovery might be the way forward for sustainable forestry and livelihoods

Do livelihood typologies influence local perceptions of forest cover change? Evidence from a tropical forested and non-forested rural landscape in western Uganda

© 2016 Elsevier LtdValidation of scientific findings from satellite remote sensing against local ecological knowledge could make the interpretation of forest cover patterns more robust. In this paper, we examine local perceptions of forest cover change in parishes around Budongo and Bugoma for a 30-year period (1985–2014), compare the results with those obtained from remote sensing (Twongyirwe et al., 2015), and interrogate whether the perceptions could be related to livelihood typologies. First, we characterise household strategies for the entire landscape to place livelihood strategies of communities in deforestated areas in a broader local context. An in-depth questionnaire was administered to 706 households in 13 parishes situated in 4 Agro-Ecological Zones (AEZs). The data included household demographic characteristics, energy use, cropping and livestock husbandry, and seasonal time- and labour-budgets. Principal Components Analysis (PCA) and Cluster Analysis (CA) were employed to help identify dominant structures in the data. Secondly, the 375 households in 7 parishes around Budongo and Bugoma forests (part of the 706) responded to additional questions that sought their perceptions on the forest cover trend. The PCA results for the entire landscape show that significant variation amongst households is mainly related to the cultivation time input, on-farm income particularly from cropping activities, livestock husbandry, demographic characteristics, agricultural extension activities, and cultivation labour input. Hierarchical CA shows that households at the landscape level fall into about nine different types, with variation in spatial distribution. The analysis suggests that poor households do live near forested regions, and that the rural poor are more reliant on forest products than peri-urban populations. Regarding perceptions of forest cover change, the majority (70.1%: n = 375) of the respondents in the parishes think that there has been a decline in forest cover, and this percentage is larger than the percentage of non-respondents (18.9%), those that thought it had increased (5.6%), not changed (3.7%), and those that did not know (1.6%). In addition, perceptions on forest change were significantly related to the household livelihood typologies (X2 = 623.4, df = 4, p = 0.000): respondents who perceived forest cover as having declined and those that provided no response belonged to cluster 2 (“low income mixed farming households”), which is also the dominant livelihood typology around these forests. While the data largely suggest that there is a remarkable agreement between remote sensing results and local knowledge on forest change, and that local people may play a big role in filling data gaps where a dearth of information is prevalent (or where remote sensing evidence is fuzzy), there is a clear signal that people in different social classes and age groups can have very different views on what the change in forest cover might be despite what the remote sensing data show. This might have policy implications if decision makers tend to come from the groups that are not likely to have perceived forest cover change, or base their judgement on views from certain social classes. This implies that it is important to have the remote sensing data available as a counter balance to local perception (and vice versa) and therefore these data should be considered concurrently

Second-Generation Objects in the Universe: Radiative Cooling and Collapse of Halos with Virial Temperatures Above 10^4 Kelvin

The first generation of protogalaxies likely formed out of primordial gas via H2-cooling in cosmological minihalos with virial temperatures of a few 1000K. However, their abundance is likely to have been severely limited by feedback processes which suppressed H2 formation. The formation of the protogalaxies responsible for reionization and metal-enrichment of the intergalactic medium, then had to await the collapse of larger halos. Here we investigate the radiative cooling and collapse of gas in halos with virial temperatures Tvir > 10^4K. In these halos, efficient atomic line radiation allows rapid cooling of the gas to 8000 K; subsequently the gas can contract nearly isothermally at this temperature. Without an additional coolant, the gas would likely settle into a locally gravitationally stable disk; only disks with unusually low spin would be unstable. However, we find that the initial atomic line cooling leaves a large, out-of-equilibrium residual free electron fraction. This allows the molecular fraction to build up to a universal value of about x(H2) = 10^-3, almost independently of initial density and temperature. We show that this is a non--equilibrium freezeout value that can be understood in terms of timescale arguments. Furthermore, unlike in less massive halos, H2 formation is largely impervious to feedback from external UV fields, due to the high initial densities achieved by atomic cooling. The H2 molecules cool the gas further to about 100K, and allow the gas to fragment on scales of a few 100 Msun. We investigate the importance of various feedback effects such as H2-photodissociation from internal UV fields and radiation pressure due to Ly-alpha photon trapping, which are likely to regulate the efficiency of star formation.Comment: Revised version accepted by ApJ; some reorganization for clarit

When defining boundaries for nexus analysis, let the data speak

A policy and research agenda has emerged in recent years to understand the interconnected risks natural resource systems face and drive. The so-called ‘Food-Energy-Water’ (FEW) nexus has served as a focal point for the conceptual, theoretical and empirical development of this agenda. This special issue provides an opportunity to reflect on whether natural resource use, as viewed through the FEW-nexus lens, provides a useful basis for guiding integrated environmental management. Within this piece, we describe how the partiality of the FEW-nexus overlooks major pathways of resource use (i) within the food system and (ii) across the wider burden of human activity. As a result, we argue FEW-centric analysis is more likely to disguise rather than reveal key opportunities for integrated environmental management.Cambridge Trust (Vice-Chancellor's Award

The Large-Scale, Systematic and Iterated Comparison of Agent-Based Policy Models

Vital to the increased rigour (and hence reliability) of Agent-based modelling are various kinds of model comparison. The reproduction of simulations is an essential check that models are as they are described. Here we argue that we need to go further and carry out large-scale, systematic and persistent model comparison—where different models of the same phenomena are compared against standardised data sets and each other. Lessons for this programme can be gained from the Model Intercomparison Projects (MIP) in the Climate Community and elsewhere. The benefits, lessons and particular difficulties of implementing a similar project in social simulation are discussed, before sketching what such a project might look like. It is time we got our act together

A fibre alginate co-culture platform for the differentiation of mESC and modelling of the neural tube

Alginate hydrogels are a commonly used substrate for in vitro 3D cell culture. These naturally derived biomaterials are highly tunable, biocompatible and can be designed to mimic the elastic modulus of the adult brain at 1% w/v solution. Recent studies show that the molecular weight of the alginate can affect cell viability and differentiation. The relationship between the molecular weight, viscosity and ratio of G:M monomers of alginate hydrogels is complex, and the balance between these factors must be carefully considered when deciding on a suitable alginate hydrogel for stem cell research. This study investigates the formation of embryoid bodies (EB) from mouse embryonic stem cells, using low molecular weight (LMW) and high molecular weight (HMW) alginates. The cells are differentiated using a retinoic acid-based protocol, and the resulting aggregates are sectioned and stained for the presence of stem cells and the three germ layers (endoderm, mesoderm and ectoderm). The results highlight that aggregates within LMW and HMW alginate are true EBs, as demonstrated by positive staining for markers of the three germ layers. Using tubular alginate scaffolds, formed with an adapted gradient maker protocol, we also propose a novel 3D platform for the patterned differentiation of mESCs, based on gradients of retinoic acid produced in situ by lateral motor column (LMC) motor neurons. The end product of our platform will be of great interest as it can be further developed into a powerful model of neural tube development

An Optical/Near-Infrared Study of Radio-Loud Quasar Environments II. Imaging Results

We use optical and near-IR imaging to examine the properties of the significant excess population of K>=19 galaxies found in the fields of 31 z=1-2 radio-loud quasars by Hall, Green & Cohen (1998). The excess occurs on two spatial scales: a component at <40'' from the quasars significant compared to the galaxy surface density at >40'' in the same fields, and a component roughly uniform to ~100'' significant compared to the galaxy surface density seen in random-field surveys in the literature. The r-K color distributions of the excess galaxy populations are indistinguishable and are significantly redder than the color distribution of the field population. The excess galaxies are consistent with being predominantly early-type galaxies at the quasar redshifts, and there is no evidence that they are associated with intervening MgII absorption systems. The average excess within 0.5 Mpc (~65'') of the quasars corresponds to Abell richness class ~0 compared to the galaxy surface density at >0.5 Mpc from the quasars, and to Abell richness class ~1.5 compared to that from the literature. We discuss the spectral energy distributions (SEDs) of galaxies in fields with data in several passbands. Most candidate quasar-associated galaxies are consistent with being 2-3 Gyr old early-types at the quasar redshifts of z~1.5. However, some objects have SEDs consistent with being 4-5 Gyr old at z~1.5, and a number of others are consistent with ~2 Gyr old but dust-reddened galaxies at the quasar redshifts. These potentially different galaxy types suggest there may be considerable dispersion in the properties of early-type cluster galaxies at z~1.5. There is also a population of galaxies whose SEDs are best modelled by background galaxies at z>2.5.Comment: Accepted to ApJ; 54 pages including 30 figures; 2 color GIF files available separately; also available from http://www.astro.utoronto.ca/~hall/thesis.htm