How dark the sky: the JWST backgrounds

We describe the sources of stray light and thermal background that affect JWST observations; report actual backgrounds as measured from commissioning and early science observations; compare those background levels to pre-launch predictions; estimate the impact of the backgrounds on science performance; and explore how the backgrounds probe the achieved configuration of the deployed observatory. We find the observatory is limited by the irreducible astrophysical backgrounds, rather than scattered stray light and thermal self-emission, for all wavelengths $\lambda < 12.5$ micron, thus meeting the level 1 requirement. This result was not assured given the open architecture and thermal challenges of JWST, and is the result of meticulous attention to stray light and thermal issues in the design, construction, integration, and test phases. From background considerations alone, JWST will require less integration time in the near-infrared compared to a system that just met the stray light requirements; as such, JWST will be even more powerful than expected for deep imaging at 1--5 micron. In the mid-infrared, the measured thermal backgrounds closely match pre-launch predictions. The background near 10 micron is slightly higher than predicted before launch, but the impact on observations is mitigated by the excellent throughput of MIRI, such that instrument sensitivity will be as good as expected pre-launch. These measured background levels are fully compatible with JWST's science goals and the Cycle 1 science program currently underway.Comment: Submitted to the "JWST Overview" special issue of PAS

LADUMA: looking at the distant universe with the MeerKAT array

The cosmic evolution of galaxies’ neutral atomic gas content is a major science driver for the Square Kilometre Array (SKA), as well as for its South African (MeerKAT) and Australian (ASKAP) precursors. Among the H I large survey programs (LSPs) planned for ASKAP and MeerKAT, the deepest and narrowest tier of the “wedding cake” will be defined by the combined L-band+UHF-band Looking At the Distant Universe with the MeerKAT Array (LADUMA) survey, which will probe H I in emission within a single “cosmic vuvuzela” that extends to z = 1.4, when the universe was only a third of its present age. Through a combination of individual and stacked detections (the latter relying on extensive multi-wavelength studies of the survey’s target field), LADUMA will study the redshift evolution of the baryonic Tully–Fisher relation and the cosmic H I density, the variation of the H I mass function with redshift and environment, and the connection between H I content and galaxies’ stellar properties (mass, age, etc.). The survey will also build a sample of OH megamaser detections that can be used to trace the cosmic merger history. This proceedings contribution provides a brief introduction to the survey, its scientific aims, and its technical implementation, deferring a more complete discussion for a future article after the implications of a recent review of MeerKAT LSP project plans are fully worked out

Implementation fidelity of the Falls Management Exercise Programme: a mixed methods analysis using a conceptual framework for implementation fidelity

Objectives: Falls in older adults cause significant morbidity and mortality and incur cost to health and care services. The Falls Management Exercise (FaME) programme is a 24-week intervention for older adults that in clinical trials improves balance and functional strength and leads to fewer falls. Similar, but more modest outcomes have been found when FaME is delivered in routine practice. Understanding the degree to which the programme is delivered with fidelity is important if ‘real world’ delivery of FaME is to achieve the same magnitude of outcome as in clinical trials. The objective of this study was to examine the implementation fidelity of FaME when delivered in the community, to inform quality improvement strategies that maximise programme effectiveness.Study design: A mixed-methods implementation study of FaME programme delivery.Methods: Data from programme registers, expert observations of FaME classes and semi-structured interviews with FaME instructors were triangulated using a conceptual framework for implementation fidelity. Quantitative data were analysed using descriptive statistics. Interviews were transcribed verbatim and analysed using thematic analysis. Results: In total 356 participants enrolled on 29 FaME programmes and 143 (40%) participants completed at least 75% of the classes within a programme. Observations showed that 72%-78% of programme content was delivered and 80%-84% quality criteria were met. Important content that was most often left out included home exercises, Tai Chi moves and floor work, whilst quality items most frequently missed out included asking about falls in the previous week, following up attendance absence and explaining the purpose of exercises. Only 24% of class participants made the expected strength training progression. Interviews with FaME instructors helped explain why elements of programme content and quality were not delivered. Strategies for improving FaME delivery were established and helped to maintain quality and fidelity. Conclusions: FaME programmes delivered in the ‘real world’ can be implemented with a high degree of fidelity, although important deviations were found. Facilitation strategies could be used to further improve programme fidelity and maximise participant outcomes