Large scale structures in the Universe

Lead Research Organisation: University College London
Department Name: Physics and Astronomy

Abstract

The PhD project will map clusters and voids in the Dark Energy Survey and other data sets, and their imprint on the Cosmic Microwave Background.

Publications

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Naidoo K (2020) Beyond two-point statistics: using the minimum spanning tree as a tool for cosmology in Monthly Notices of the Royal Astronomical Society

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Naidoo K (2019) MiSTree: a Python package for constructing and analysing Minimum Spanning Trees in Journal of Open Source Software

Studentship Projects

Project Reference Relationship Related To Start End Student Name
ST/N50449X/1 30/09/2015 30/03/2021
1783821 Studentship ST/N50449X/1 30/09/2016 30/03/2020 Krishna Naidoo
 
Title If a tree falls in a forest 
Description A collaboration between artist from the Royal College of Arts and cosmologist from Universty College London. Pairs of artist and scientist came together to produce a small exhibition piece on their current research. Ours involved creating a a scuptural piece displaying the minimum spanning tree methodology and a video projected on a dome showing how a particular algorithm finds this data. This was combined with a musical piece which was constructed algorithmically and displayed on stars from the night sky. 
Type Of Art Artistic/Creative Exhibition 
Year Produced 2018 
Impact The collaboration helped me realise the many similarities between artist and scientist as well as helped me understand my research in ways I had not seen prior. The exhibition also provided me with lots of lessons about how I should go about communicating my research to an audience that is not familiar with the technicalities of the work. 
URL http://ifatreefalls.rca.ac.uk
 
Description Very broadly we wanted to determine whether a new statistics could be developed for analysing the large scale distribution of matter in the Universe. This is pivotal for future galaxy surveys that will map the positions of millions of galaxies. Our core purpose was to determine whether the cosmic web (the way in which matter clusters in a filamentary web like structure) could be captured statistically and used to determine whether what we see in galaxies matches what we see in simulations. We determined that the minimum spanning tree (MST), could be used as such a statistics and could be used with existing and more conventional statistical methods for determining parameters of the cosmological model and testing new physics. In particular we have shown in my PhD thesis that the statistics is very sensitive to neutrino mass, of keen interest to physicist as the mass of these elusive particles remains unknown. The application to real data still requires some work. We have made great progress in understanding how we can mitigate common systematic issues from galaxy surveys and have compared the MST on real and simulated data from the Baryon Oscillation Spectroscopic Survey.
Exploitation Route The statistical methods used have a broad application. The minimum spanning tree statistics and the public software created for this study can be used for a wide range of studies which look to characterise point distributions. The software has been download over 9000 times with studies employing it in other areas of science, including star cluster studies.
Sectors Digital/Communication/Information Technologies (including Software)

Other

 
Title Minimum Spanning Tree 
Description Using decision maths we have investigated the use of the Minimum Spanning Tree to try and capture topological information present in Large galaxy redshift surveys. 
Type Of Material Data analysis technique 
Year Produced 2019 
Provided To Others? Yes  
Impact Although not in use yet, as we currently writing a paper on the subject, the minimum spanning tree is expected to improve our knowledge on the constants that define our model of the universe. 
 
Description Integrated Sachs-Wolfe for Lightcone Simulations 
Organisation University of Barcelona
Department Institute for Space Studies of Catalonia (IEEC)
Country Spain 
Sector Academic/University 
PI Contribution I have created Integrate Sachs-Wolfe maps for the MICE and Flagship lightcone simulations. This will allow for cross correlation studies to be carried out between large galaxys surveys and the cosmic microwave background (CMB). I will additionally make the c++ pipeline public so that ISW maps can be created from future lightcone simulations.
Collaborator Contribution I have worked closely with Pablo Fosalba (based in Barcelona) who has provided me with the MICE and Flagship lightcone simulations.
Impact We will eventually make the ISW maps and code created in this study public.
Start Year 2019
 
Description Simulations for minimum spanning tree 
Organisation International School for Advanced Studies
Country Italy 
Sector Academic/University 
PI Contribution We have been working on a project designed for future use on large scale galaxy redshift surveys. We have been exploring a new statistics which is designed to pick up information not currently used in cosmology. The hope is this will better constrain parameters used to describe the universe we live in. We have been exploring its application in a variety of settings, systematics consideration. Additionally a major challenge has been to tie down future observations with theoretical expectations, since the statistics can not be predicted analytically we have to resort to state of the art simulations. We plan to release a public code to allow others in the community to run a similar analysis.
Collaborator Contribution Our partners (Elena Massara, Matteo Viel) have provided state of the art N-body simulations. Whilst Hector Gil-Marin has supplied us with a piece of code to calculate bispectrum measurements from data. Bispectrum are analytically and observationally difficult measurements to make so we resort to using a tried and tested code for this calculation since our aim is to simply compare methodologies.
Impact We are currently writing a paper to detail our work on this new statistic and plan to use it on the existing Baryon Oscillation Spectrocopic Survey and the future Dark Energy Spectrocopic Survey.
Start Year 2017
 
Description Simulations for minimum spanning tree 
Organisation Simons Foundation
Department Flatiron Institute
Country United States 
Sector Academic/University 
PI Contribution We have been working on a project designed for future use on large scale galaxy redshift surveys. We have been exploring a new statistics which is designed to pick up information not currently used in cosmology. The hope is this will better constrain parameters used to describe the universe we live in. We have been exploring its application in a variety of settings, systematics consideration. Additionally a major challenge has been to tie down future observations with theoretical expectations, since the statistics can not be predicted analytically we have to resort to state of the art simulations. We plan to release a public code to allow others in the community to run a similar analysis.
Collaborator Contribution Our partners (Elena Massara, Matteo Viel) have provided state of the art N-body simulations. Whilst Hector Gil-Marin has supplied us with a piece of code to calculate bispectrum measurements from data. Bispectrum are analytically and observationally difficult measurements to make so we resort to using a tried and tested code for this calculation since our aim is to simply compare methodologies.
Impact We are currently writing a paper to detail our work on this new statistic and plan to use it on the existing Baryon Oscillation Spectrocopic Survey and the future Dark Energy Spectrocopic Survey.
Start Year 2017
 
Description Simulations for minimum spanning tree 
Organisation University of Barcelona
Country Spain 
Sector Academic/University 
PI Contribution We have been working on a project designed for future use on large scale galaxy redshift surveys. We have been exploring a new statistics which is designed to pick up information not currently used in cosmology. The hope is this will better constrain parameters used to describe the universe we live in. We have been exploring its application in a variety of settings, systematics consideration. Additionally a major challenge has been to tie down future observations with theoretical expectations, since the statistics can not be predicted analytically we have to resort to state of the art simulations. We plan to release a public code to allow others in the community to run a similar analysis.
Collaborator Contribution Our partners (Elena Massara, Matteo Viel) have provided state of the art N-body simulations. Whilst Hector Gil-Marin has supplied us with a piece of code to calculate bispectrum measurements from data. Bispectrum are analytically and observationally difficult measurements to make so we resort to using a tried and tested code for this calculation since our aim is to simply compare methodologies.
Impact We are currently writing a paper to detail our work on this new statistic and plan to use it on the existing Baryon Oscillation Spectrocopic Survey and the future Dark Energy Spectrocopic Survey.
Start Year 2017
 
Title MiSTree 
Description MiSTree is a public python software used to construct and analyse data using the minimum spanning tree method we have outlined. The software has been complete for some time but is not publicly released yet but is planned to be released on an MIT licence. 
Type Of Technology Software 
Year Produced 2019 
Open Source License? Yes  
Impact The software is used through out our methodology paper on the use of the minimum spanning tree for research in cosmology. 
URL https://knaidoo29.github.io/mistreedoc/