SKA Weak Lensing III: Added Value of Multi-Wavelength Synergies for the Mitigation of Systematics

In this third paper of a series on radio weak lensing for cosmology with the Square Kilometre Array, we scrutinise synergies between cosmic shear measurements in the radio and optical/near-IR bands for mitigating systematic effects. We focus on three main classes of systematics: (i) experimental systematic errors in the observed shear; (ii) signal contamination by intrinsic alignments; and (iii) systematic effects due to an incorrect modelling of non-linear scales. First, we show that a comprehensive, multi-wavelength analysis provides a self-calibration method for experimental systematic effects, only implying <50% increment on the errors on cosmological parameters. We also illustrate how the cross-correlation between radio and optical/near-IR surveys alone is able to remove residual systematics with variance as large as 0.00001, i.e. the same order of magnitude of the cosmological signal. This also opens the possibility of using such a cross-correlation as a means to detect unknown experimental systematics. Secondly, we demonstrate that, thanks to polarisation information, radio weak lensing surveys will be able to mitigate contamination by intrinsic alignments, in a way similar but fully complementary to available self-calibration methods based on position-shear correlations. Lastly, we illustrate how radio weak lensing experiments, reaching higher redshifts than those accessible to optical surveys, will probe dark energy and the growth of cosmic structures in regimes less contaminated by non-linearities in the matter perturbations. For instance, the higher-redshift bins of radio catalogues peak at z~0.8-1, whereas their optical/near-IR counterparts are limited to z<0.5-0.7. This translates into having a cosmological signal 2 to 5 times less contaminated by non-linear perturbations.Comment: 16 pages, 10 figures, 2 tables; improved discussion of experimental systematics in Sec. 2; updated to match published versio

SKA Weak Lensing II: Simulated Performance and Survey Design Considerations

We construct a pipeline for simulating weak lensing cosmology surveys with the Square Kilometre Array (SKA), taking as inputs telescope sensitivity curves; correlated source flux, size and redshift distributions; a simple ionospheric model; source redshift and ellipticity measurement errors. We then use this simulation pipeline to optimise a 2-year weak lensing survey performed with the first deployment of the SKA (SKA1). Our assessments are based on the total signal-to-noise of the recovered shear power spectra, a metric that we find to correlate very well with a standard dark energy figure of merit. We first consider the choice of frequency band, trading off increases in number counts at lower frequencies against poorer resolution; our analysis strongly prefers the higher frequency Band 2 (950-1760 MHz) channel of the SKA-MID telescope to the lower frequency Band 1 (350-1050 MHz). Best results would be obtained by allowing the centre of Band 2 to shift towards lower frequency, around 1.1 GHz. We then move on to consider survey size, finding that an area of 5,000 square degrees is optimal for most SKA1 instrumental configurations. Finally, we forecast the performance of a weak lensing survey with the second deployment of the SKA. The increased survey size (3$\pi$\,steradian) and sensitivity improves both the signal-to-noise and the dark energy metrics by two orders of magnitude.Comment: 15 pages, 11 figures, 1 table. Comments welcome. Updated to match published versio

Investigations into the Hyporheic Zone: Assessing the Influence of Groundwater-Surface Water Interactions on Metal Exposure and Effects to Aquatic Ecosystems

Metal contaminated sediments are a common stressor of biological communities in freshwater ecosystems. Sediments have the capacity to store metals (via various chemical binding ligands in sediments), rendering them unavailable for uptake by biological communities. Physical processes in streams, however, can influence the chemistry of sediments and ultimately control how sediments store metals. Groundwater-surface water interactions (hyporheic flows) are an example of a natural physical process that influences sediment chemistry and potentially the exposure of metals to aquatic biota. Hyporheic flows are generally characterized as either ‘downwelling’ (surface water entering streambed sediments) or ‘upwelling’ (from sediments into surface water). Flow direction can be related to the location in a stream riffle, as downwelling typically occurs at the head (upstream end) of a riffle and upwelling occurs on the tail (downstream end) of a riffle. Using multiple lines of evidence (field, mesocosm, and laboratory studies), this dissertation investigated the role of hyporheic flows on metal exposure and effects to aquatic organisms. Depending on the experiment, biological assessments included: test organism (Hyalella azteca) survival, benthic macroinvertebrate community composition, and biofilm structure and function. In the in situ experiments in Chapter 2, the heads of riffles were more oxidized and had greater benthic macroinvertebrate diversity and more sensitive species than the tails of riffles. Flow-through experiments in Chapter 2 also observed more oxidized sediments in downwelling conditions, compared to mesocosms without downwelling. In Chapter 3, oxygenated (oxic) hyporheic flows (downwelling) increased the bioavailability of metals, and subsequent declines in H. azteca survival were observed. In Chapter 4, the in situ experiments at field sites with upwelling hyporheic flows showed that sediments exposed to upwelling zones had less oxygen (were more reduced) and metals were less bioavailable than sediments not exposed to hyporheic upwelling. This research demonstrates the importance of hyporheic flows on redox-sensitive binding ligands and the subsequent effects on aquatic biological communities. It also suggests that inclusion of hyporheic flows in ecological risk assessments could more accurately characterize metal exposure pathways to aquatic biota.PHDNatural Resources & EnvironmentUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144068/1/annaha_1.pd

‘Where Have You Vanished?’: Aelred of Rievaulx’s Lamentation on Simon

In his lamentation on the death of his friend, Simon, Aelred responds to a centuries-long suspicion about grief by mounting an apology for mourning that is in keeping with a larger Cistercian trend. Aelred’s chief preoccupation in the lamentation is, however, to emphasize the productivity of grief, both for the living and for the dead. Aelred associates the desire to reunite with the beloved dead with stimulating the mourner’s desire for heaven as location for the longed-for reunion, and he conceives of the pain associated with bereavement as payment for the sins of the deceased