Spinning galaxies within the large scale structure of the Universe

Finding links between the large scale structure of the Universe and galaxy formation presents an important challenge for cosmology. The properties of dark matter halos in N-body simulations, in particular the spin angular momentum, can provide these links. This thesis is an in depth study of the alignments of halo spin direction within filaments in the large scale structure. Filaments in the halo and galaxy distribution of the Millennium simulation were identified using two simple methods and a difference between the spin orientation of low and high mass halos with the axis of filaments was uncovered. The evolution of these alignments and other aspects of halo spin suggested an ongoing process of angular momentum acquisition. This process was found to be largely reliant on the anisotropic infall of satellite halos. The spin of dark matter halos tends to become increasingly parallel to the axis of filaments and this change is driven by major mergers between halos traveling orthogonal to the axis of filaments. This new scenario of the build-up of dark matter halo spin could see significant consequences in theories of galaxy formation

Making lab 'pre-work' work

Laboratory classes are a key part of first year physics but, for many students, the objective is to complete the task and get out! How do we engage students more effectively with the lab experience? One means of increasing engagement is 'pre-work' completed before the lab classes. We have begun a program to move our lab pre-work from a pen-and-paper exercise to on-line learning with the primary aim to offer students a much improved introduction to the apparatus and the physics of each session. Student surveys indicate that online pre-work is popular and a better introduction than its paper-based precursor, with 82% of students agreeing that the extra information in the pre-work module was useful to them. [a brief summary extracted from the full Abstract

Constraining the runaway dilaton and quintessential dark energy

Dark Energy is some of the weirdest and most mysterious stuff in the universe that tends to increase the rate of expansion of the universe. Two commonly known forms of dark energy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli whose energy density can vary with time. We explore one particular model for dynamic dark energy; quintessence driven by a scalar dilaton field. We propose an ansatz for the form of the dilaton field, $|\phi(a)|/m_P \equiv \alpha_1 \ln t+ \alpha_2 t^n=\alpha\ln a+ \beta\, a^{2\zeta}$, where $a$ is the scale factor and $\alpha$ and $\zeta$ are parameters of the model. This phenomenological ansatz for $\phi$ can be motivated by generic solutions of a scalar dilaton field in many effective string theory and string-inspired gravity models in four dimensions. Using a compilation of current data including type Ia supernovae, we impose observational constraints on the slope parameters like $\alpha$ and $\zeta$ and then discuss the relation of our results to analytical constrains on various cosmological parameters, including the dark energy equation of state. Sensible constraints are imposed on model parameters like $\alpha$ and $\zeta$ as well as on the dark energy/dark matter couplings using results from structure formation. The constraints of this model are shown to encompass the cosmological constant limit within $1\sigma$ error bars.Comment: 32 pages, several eps figures; refs added, matches published versio

The Sydney-AAO Multi-object Integral field spectrograph (SAMI)

We demonstrate a novel technology that combines the power of the multi-object spectrograph with the spatial multiplex advantage of an integral field spectrograph (IFS). The Sydney-AAO Multi-object IFS (SAMI) is a prototype wide-field system at the Anglo-Australian Telescope (AAT) that allows 13 imaging fibre bundles ("hexabundles") to be deployed over a 1-degree diameter field of view. Each hexabundle comprises 61 lightly-fused multimode fibres with reduced cladding and yields a 75 percent filling factor. Each fibre core diameter subtends 1.6 arcseconds on the sky and each hexabundle has a field of view of 15 arcseconds diameter. The fibres are fed to the flexible AAOmega double-beam spectrograph, which can be used at a range of spectral resolutions (R=lambda/delta(lambda) ~ 1700-13000) over the optical spectrum (3700-9500A). We present the first spectroscopic results obtained with SAMI for a sample of galaxies at z~0.05. We discuss the prospects of implementing hexabundles at a much higher multiplex over wider fields of view in order to carry out spatially--resolved spectroscopic surveys of 10^4 to 10^5 galaxies.Comment: 24 pages, 16 figures. Accepted by MNRA

LATENT DRIVERS OF PLAYER RETENTION IN JUNIOR RUGBY

To help key stakeholders cultivate an environment that fosters long-term participation in rugby, drivers that encourage young athletes to remain in the sport must be identified and understood. This study investigates the latent drivers of engagement in a junior rugby system for better data informed decisions. This study then demonstrates how combining administrative data with dynamic social datasets objectifies biased perceptions to some degree. Administration-level data was collected each annual season across a three-year period (2017-2019) by the Auckland Rugby Union and analysed to identify the predictors of player retention. Players were categorised according to whether they remained in (or departed from) the sport at the end of each playing season. A multivariate logistic regression model with a stepwise AIC variable selection was employed to identify significant independent predictors of player retention. Squad size, rugby sentiment in the media and deprivation were significant contributors to junior rugby player retention. This demonstrates that player retention is not only driven by weight and peer group participation, which has been the main focus of engaging juniors in rugby in the past, there are other social factors associated with churn