Undergrad Presentations - Aviv Padawer-Blatt, Lauren Foster and Justin Marchioni

Lauren Foster

Lauren Foster is a fourth-year undergraduate student in the Physics and Astronomy program at Waterloo. She started working with Dr. Percival in May 2021 on a project exploring the use of machine learning to identify dark matter halos in redshift-space.

Talk Title and Abstract:

Machine Learning Approach to Identifying Halos From Particles in Redshift-space

This summer I explored the use of machine learning to identify dark matter halos in redshift-space with Prof. Will Percival and Dr. Andrej Obuljen. In the talk, I will explain our method of using dark matter N-body simulations, in which we know the positions of the particles in both real and redshift-space, and supervised learning techniques with the goal of being able to identify what real-space halo each particle corresponds to, using only the redshift-space information. To see the effectiveness of this method, I will compare against two commonly used halo finders, and I will explain both the benefits and limitations of the supervised learning approach to identifying dark matter halos.

Aviv Padawer-Blatt

I currently study at the University of Waterloo as an undergraduate Physics and Astronomy student, and am eager to engage in different research experiences. I found a passion this past summer in Cosmology, specifically Large Scale Structure research, with Shahab Joudaki, Will Percival and Will’s group. My hope is to continue with Cosmology, learning as much as possible, gathering experience and making discoveries about the nature of the universe.

Talk Title and Abstract:

Does Modified Gravity Solve the S₈ Tension?

The statistical discordance under the standard ΛCDM framework in the cosmological parameter S₈, which combines the amplitude of growth of structure and the matter energy density in the universe, has become a common finding in Cosmology. This tension is prevalent between the Cosmic Microwave Background (CMB) anisotropies (specifically the Planck data) and weak gravitational lensing measurements. We focus on attempting to resolve this observed tension between weak lensing measurements from the Kilo-Degree Survey (KiDS-1000) and the Planck 2018 CMB data with a model-independent extension to General Relativity. At the same time, we require any tested Modified Gravity model to be favoured in a Bayesian model selection sense. To this end, we investigate different Modified Gravity parametrizations, including binning in redshift and scale or functional dependence on redshift and scale. Our findings indicate that none of the Modified Gravity models in question simultaneously resolve the S₈ tension and are favoured in a model selection sense. The only extension to ΛCDM that allows both above conditions concurrently is one in which the CMB lensing amplitude (A_lens) is additionally varied, which however is an extension that is not motivated by any underlying physical theory.

Justin Marchioni

Justin Marchioni is a 4th year student at the University of Waterloo (UW) studying Physics and Astronomy. During the summer of 2021, he worked with Dr. Michael Balogh (Professor, UW) studying how the stellar mass function of galaxies in dense environments at 0.8 < z < 1.5 varies with redshift and halo mass. While completing the final year of his bachelor’s degree, he is currently working with Dr. James Taylor (Associate Professor, UW) studying the effect of mergers on the structure of dark matter haloes.

Talk Title and Abstract:

The Stellar Mass Function of Galaxies in Dense Environments at 0.8 < z < 1.5 and its Variation with Redshift and Halo Mass

In 2020, the first data release of the GOGREEN and GCLASS surveys were made publicly available. The surveys consist of deep, multiwavelength photometry and extensive spectroscopy of galaxies in 26 dense environments spanning a redshift range 0.8 < z < 1.5 and halo masses ranging from small groups to the most massive clusters. One of the original goals of the surveys was to measure the stellar content in these haloes. In this talk, I will showcase our results for the stellar mass functions (SMFs) of star-forming and quiescent galaxies in overdense systems as a function of redshift and halo mass. I will discuss our methodology for filtering the dataset, how we weight each galaxy to calculate the SMF, and how we fit a Schechter function to the data to model the SMF. Finally, I will illustrate the stellar-to-halo mass relation we find for these systems and compare it to other results found in literature.

Would you like to join this Zoom seminar? Please email WCA.