Measuring the distribution of stars and dark matter in galaxy-scale strong gravitational lenses: lessons from an automated approach

In this thesis, I constrain the distributions of mass and light of the largest sample of galaxy-scale strong lens systems modelled using an automated approach to this date. New surveys will soon observe hundreds of thousands of galaxy lenses requiring reliable automated methods to be exploited. With this in mind, I present not only the successful model fit results, but also the reasons why some lenses failed initially and the strategies we adopted to ultimately fit all the galaxies with minimal intervention. I discuss what we can learn from this process that could benefit future large scale studies. I propose and evaluate a likelihood cap method to avoid the underestimation of errors due to noisy likelihood evaluations that appear in pixel-based source reconstruction methods. I test the method on a large sample of mock galaxies which significantly improves the coverage probabilities on all of the model parameters. With this approach to error estimation I find that the Einstein radius is typically constrained to $\sim1\%$ and the errors on the model parameters including density profile slope do not degrade with redshift. This will be beneficial for studies of galaxy evolution. I measure an average mass density slope of $\langle\gamma\rangle=2.075_{-0.024}^{+0.023}$ with little intrinsic scatter $\sigma_\gamma=0.172^{+0.022}_{-0.032}$ for the (typically) early-type galaxies acting as lenses in our sample. This is consistent with those measured using an independent lensing and dynamics approach. More generally, this result supports the empirical coincidence that the total mass profiles of early-type galaxies can be well described by a single power law -- known as the `bulge-halo conspiracy'. However, I reveal a $3\sigma$ disagreement between our measurements of the coefficient describing the relationship between slope and surface mass density $\frac{\partial\langle\gamma\rangle}{\partial\Sigma_\textrm{tot}} = -0.432^\text{+0.175}_\text{-0.191}$ and that inferred for the slopes measured using the independent method. This can potentially be explained by finer structure in the mass density profile. Finally, I demonstrate that the `external shear' parameters commonly adopted in strong lens models can not be assumed to represent perturbations only external to the mass model. Instead, they highlight the inability of the power law to fit the distribution of mass in these types of galaxies. Future strong lensing studies will require more complex mass models to appropriately describe the lens galaxy, and avoid biases on high precision measurements of galaxy masses, cosmological parameters $H_0$, and dark matter substructures

The “External” Shears In Strong Lens Models

The distribution of mass in galaxy-scale strong gravitational lenses is often modelled as an elliptical power law plus ‘external shear’, which notionally accounts for line-of-sight galaxies and cosmic shear. We argue that it does not, using three lines of evidence from the analysis of 54 galaxy-scale strong lenses: (i) strong lensing external shears do not correlate with weak lensing; (ii) the measured shear magnitudes in strong lenses (which are field galaxies) are too large (exceeding 0.05) for their environment and; (iii) the external shear position angle preferentially aligns or anti-aligns with the mass model position angle, indicating an internal origin. We argue the measured strong lensing shears are therefore systematically accounting for missing complexity in the canonical elliptical power-law mass model. If we can introduce this complexity into our lens models, this will further lensing studies of galaxy formation, dark matter and Cosmology

Leadership en matière de recherche pour le développement : document de synthèse 2

English version available in IDRC Digital Library: Integrating organizational strengthening into program design : key questions for consideratio

Leadership en matière de recherche pour le développement : document de synthèse 3

English version available in IDRC Digital Library: Funding modalities for organizational strengthening in research for developmen

Leadership in research for development series : brief 4

French version available in IDRC Digital Library: Qui sont les leaders de demain? : aborder l'égalité des genres et l'inclusion dans le leadershipFunders have a key role to play in ensuring that gender and inclusion considerations form part of selection criteria, team composition, project design, implementation and engagement. This brief explores how to address gender equality and inclusion in supporting research for development (R4D) leaders at both individual and organizational levels. This requires an understanding of who has traditionally participated in the field, which groups are underrepresented and the challenges marginalized groups may face. Explicit strategies are needed to support a diversity of emerging leaders, as well as target setting for engaging researchers from marginalized backgrounds

Leadership en matière de recherche pour le développement : document de synthèse 4

English version available in IDRC Digital Library: Who are the leaders of tomorrow? : addressing gender equality and inclusion in leadershi

Leadership en matière de recherche pour le développement : document de synthèse 1

English version available in IDRC Digital Library: Strengthening leadership : lessons from research leaders of today and tomorro

Leadership in research for development series : brief 1

French version available in IDRC Digital Library: Renforcer le leadership : les leçons des chefs de file de la recherche d’aujourd’hui et de demainThe evaluation assesses leadership strengthening in IDRC-funded award programs with the aim of understanding how best to support graduate students and early career researchers. It identifies some of the key features regarding good research for development (R4D) leadership, such as expertise in the field, and some lesser-known qualities including the capacity to inspire and empower others through collaborative approaches. Funders can draw lessons from this research, given how alumni in the Global South understand the strengths of good R4D leaders. They can support R4D leadership through individual awards programs and research grants

Leadership in research for development series : brief 2

French version available in IDRC Digital Library: Intégrer le renforcement organisationnel dans la conception des programmes : questions clés à prendre en compteWhile the provision of effective funding support typically requires a fluid, tailored partnership rather than a formulaic approach, patterns emerge around the types of questions that funders can ask themselves. This brief uses the “Evaluation of IDRC’s Contribution to Building Leading Organizations” to share lessons on how to incorporate organizational strengthening. It suggests questions to consider in program design and implementation, with the aim of informing how research for development (R4D) funders can foster leading organizations and networks

Leadership in research for development series : brief 3

French version available in IDRC Digital Library: Modalités de financement pour le renforcement organisationnel dans la recherche pour le développementFunding modalities that enable organizational strengthening typically include core funding, flexible research grants and strategic organizational development (OD) support programs. These modalities have demonstrated contributions to higher-quality research, better positioning for use, networking and partnerships, while facilitating internal learning processes. This policy brief covers how to fund for organizational strengthening. Feedback from two IDRC evaluations suggested for instance, that tailored support from program officers emerged as a more important factor for effectiveness than the provision of support for any specific length of time