Advancing weak lensing and intrinsic galaxy alignment studies into the era of precision cosmology

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

Abstract

Cosmologists can nowadays successfully explain the key features of the Universe in a consistent framework. However it is puzzling that 95% of the cosmic ingredients appear to be in exotic forms of matter whose nature is still obscure. One finds that all astronomical objects, ranging from galaxies up to the largest structures, weigh more than the amount of light which they emit suggests. Hence, the majority of matter must be of a yet unknown, non-luminous type, termed dark matter. Furthermore, the geometry of the Universe and its accelerating expansion hint at the existence of dark energy, an even more exotic component that supposedly makes up three quarters of the total cosmic energy budget.

Gravitational lensing is one of the most powerful ways of revealing the nature of dark matter and dark energy. Einstein's theory of relativity tells us that massive bodies deflect light such that a galaxy can focus the light from a background source like a magnifying glass - it acts as a gravitational lens. Similar to the effects close to the rim of a magnifying glass, the images of distant galaxies are distorted by the deflections of light by the matter along the line of sight. Measuring these tiny distortions on billions of galaxies, we can probe the distribution of matter between those galaxies and Earth, which in turn is determined by the properties of dark matter and dark energy. This method of analysing large numbers of distorted galaxy images with statistical tools is called cosmic shear.

My work aims at determining the properties of the dark building blocks of the Universe with high precision, using cosmic shear measured on large fractions of the sky. I am going to combine measurements of galaxy image distortions with those of galaxy positions, velocities, and distances to go even further and test whether our theory of gravity is still correct on cosmological scales. To make the most of upcoming cosmological data sets, as e.g. produced by the European Euclid satellite whose design I have contributed to, I am going to develop and apply new measurement methods and analysis tools which allow us to access information that has remained unused hitherto.

Obtaining highly accurate measurements is crucial, but it is equally important that they do not suffer from so-called "systematic errors": undetected deviations from the true result which would produce wrong answers and lead us to incorrect conclusions, much like measuring masses with a balance that has a faulty scale. A serious systematic error is caused by galaxies which are deformed and aligned by the gravitational pull exerted by matter in their neighbourhood. This effect, called intrinsic alignment, mimics the distortions that we want to measure in cosmic shear and thus causes strong systematic errors if ignored.

However, intrinsic galaxy alignment is not only a nuisance to cosmic shear measurements, but can provide us with valuable insight into processes of galaxy formation and evolution which are still largely unknown at present. To improve both our understanding of galaxies and the control of cosmic shear systematic errors, I will undertake the hitherto biggest effort of measuring and analysing intrinsic alignments, combining large data sets taken with telescopes at the world's best observational sites on Hawaii and the Canary Islands, in the Atacama desert and Australia.

By studying cosmic shear and intrinsic galaxy alignments jointly, I will be able to extract a maximum of information from each of these cosmological probes, yielding unique insights into both the dark and bright Universe.

Publications

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Asgari Marika (2016) Flat-Sky Pseudo-Cls Analysis for Weak Gravitational Lensing in ArXiv e-prints

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Blake Chris (2016) RCSLenS: testing gravitational physics through the cross-correlation of weak lensing and large-scale structure in Monthly Notices of the Royal Astronomical Society

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Duncan C (2014) On the complementarity of galaxy clustering with cosmic shear and flux magnification in Monthly Notices of the Royal Astronomical Society

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Duncan CA (2016) Cluster mass profile reconstruction with size and flux magnification on the STAGES survey. in Monthly notices of the Royal Astronomical Society

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Duncan Christopher A. J. (2016) Cluster mass profile reconstruction with size and flux magnification on the HST STAGES survey in Monthly Notices of the Royal Astronomical Society

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Duncan Christopher A. J. (2016) Cluster mass profile reconstruction with size and flux magnification on the HST STAGES survey in Monthly Notices of the Royal Astronomical Society

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Hildebrandt H. (2016) RCSLenS: The Red Cluster Sequence Lensing Survey in Monthly Notices of the Royal Astronomical Society

Related Projects

Project Reference Relationship Related To Start End Award Value
ST/J004421/1 01/10/2012 30/09/2013 £432,895
ST/J004421/2 Transfer ST/J004421/1 01/10/2013 31/03/2018 £351,642
 
Description * determined comprehensive view of statistical properties of covariance
* extended semi-analytic approaches to galaxy formation and evolution to include mechanisms of galaxy alignments
* contributed to joint galaxy clustering and gravitational lensing analysis that constrained laws of gravity
* introduced new covariance estimator to astrophysics
* discovered common alignment mechanism for elliptical galaxies and galaxy clusters
* led LSS joint probes cosmological analysis
Exploitation Route * properties of covariances critical for all situations where likelihood calculations and inference problems occur, e.g. risk management in finance
* semi-analytic models important tool to create realistic models of galaxy properties needed for all forthcoming cosmological galaxy surveys
* cosmological constraints might point to deficiencies in current cosmological standard model
Sectors Education,Financial Services, and Management Consultancy,Culture, Heritage, Museums and Collections

 
Description My work has cultural impact, achieved by regular outreach activities. Specifically, my work contributes to the state of the art of large-scale structure cosmology and new insights into our cosmological model (incl. dark energy and dark matter).
Sector Culture, Heritage, Museums and Collections,Other
Impact Types Cultural

 
Description ISSI International Team
Amount SFr. 22,000 (CHF)
Organisation International Space Science Institute (ISSI) 
Sector Academic/University
Country Switzerland
Start 02/2016 
End 10/2016
 
Description ISSI International Team
Amount SFr. 22,000 (CHF)
Organisation International Space Science Institute (ISSI) 
Sector Academic/University
Country Switzerland
Start 11/2013 
End 07/2014
 
Description NASA ATP Award (foreign Co-I)
Amount $620,000 (USD)
Organisation National Aeronautics and Space Administration (NASA) 
Sector Public
Country United States
Start  
 
Description Royal Society Equipment Grant
Amount £15,000 (GBP)
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom
Start 03/2013 
End 03/2014
 
Description DES 
Organisation Dark Energy Survey (DES)
Country Global 
Sector Charity/Non Profit 
PI Contribution infrastructure contributions to survey analysis
Collaborator Contribution data access for myself and my PDRAs/students; membership in working groups
Impact none yet
Start Year 2015
 
Description Euclid 
Organisation UK Space Agency
Department Euclid Consortium
Country France 
Sector Charity/Non Profit 
PI Contribution Predictive pipeline for science performance of Euclid Justification of photometric redshift requirements Simulation tool for validation of Euclid data products
Collaborator Contribution full access to Euclid data
Impact ESA Space Mission to be launched in 2021
Start Year 2009
 
Description KiDS 
Organisation European Southern Observatory (ESO)
Department VST
Country Chile 
Sector Academic/University 
PI Contribution infrastructure contributions to data analysis
Collaborator Contribution full data access to value-added weak lensing quality data analysis
Impact early data publications: public data release; refereed publications; press release
Start Year 2013
 
Description LSST 
Organisation LSST Corporation
Country United States 
Sector Charity/Non Profit 
PI Contribution contributed to MoU between UCL and LSST member of LSST DESC membership committee Co-PI of UK PPRP proposal executive group member for LSST:UK
Collaborator Contribution membership in working groups incl. leadership roles, membership of 4 PDRA/PhD
Impact Co-PI of MoU between LSST and STFC full membership of Dark Energy Science Collaboration
Start Year 2014
 
Description PAUS 
Organisation Autonomous University of Barcelona (UAB)
Country Spain 
Sector Academic/University 
PI Contribution Co-PI, provided funding and in-kind infrastructure contributions; on survey management board
Collaborator Contribution developed narrow-band camera for WHT; developed analysis pipeline and data management; internationally cordinated bids for observing time
Impact in survey mode since 2016; data analysis underway
Start Year 2015
 
Title FLASK 
Description Cosmological random field simulations 
Type Of Technology Software 
Year Produced 2016 
Open Source License? Yes  
Impact now widely used by survey collaborations, incl. Euclid and DES 
URL http://adsabs.harvard.edu/abs/2016ascl.soft06015X
 
Title Weak lensing verification simulations 
Description code based on random fields to produce simulated weak lensing catalogues with known underlying signal, which can be used to verify performance of codes that generate weak lensing data products 
Type Of Technology Software 
Year Produced 2013 
Impact used for code verification at Level 3 in ESA Euclid ground segment pipeline development; instrumental to assess code performances 
 
Description ATI Summit 'Big data in the physical sciences' 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Main organiser of ATI Exploiter Summit for STFC-related subject areas
Year(s) Of Engagement Activity 2016
 
Description Benasque meeting 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact 2-week international meeting with expert discussion sessions; led discussion session and presented key results of my work
Year(s) Of Engagement Activity 2017
 
Description Conference "Interplay between particle and astrophysics" 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact information PP community about Euclid astrophysics mission, initiated discussion

plans for stronger engagement between London PP and AP groups
Year(s) Of Engagement Activity 2014
 
Description ESO/Max-Planck conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact reviewed challenges in the field of weak lensing to world-leading researchers

sparked several discussion with leading researchers in the field and beyond
Year(s) Of Engagement Activity 2015
 
Description Euclid Intrinsic Alignments tiger team coordinator 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact coordinator of international group to tackle urgent problem of intrinsic alignment contamination in ESA Euclid data, so far resulting in revised Euclid requirements, and coordinated effort to develop models and gain more data

group invited to write topical review for Space Science Reviews
Year(s) Of Engagement Activity 2011,2012,2013,2014
 
Description IAU Symposium Lisbon 2014 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact ~150 researcher (both astrophysics and statistics) attended talk on statistical properties of covariance

feedback from attendees that they are grateful for being made aware of important effects previously ignored and clear explanations
Year(s) Of Engagement Activity 2014
 
Description ING conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact informed broad audience about the Euclid mission

clarified scope and status of Euclid mission to broad audience
Year(s) Of Engagement Activity 2015
 
Description ISSI workshops 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Organiser of 2 week-long workshops at ISSI, produced joint strategy to overcome problem of intrinsic alignments for Euclid Space Mission

Revision of requirements, calibration data, and analysis methodology for Euclid Mission
Year(s) Of Engagement Activity 2013,2014
 
Description KiDS press release 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Media (as a channel to the public)
Results and Impact positive feedback mostly from colleagues

unknown
Year(s) Of Engagement Activity 2015
URL http://blogs.ucl.ac.uk/science/2015/07/09/hitting-rewind-on-cosmic-history/
 
Description Lorentz Workshop 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact updated world-leading researcher about the field of intrinsic galaxy alignments

leading researchers re-evaluated their assessement of the importance of intrinsic alignments
Year(s) Of Engagement Activity 2015
 
Description Public Lectures 'Bend it like Einstein' 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact several public lectures in the London area
Year(s) Of Engagement Activity 2016,2017
 
Description RAS Specialist Discussion Meeting on LSST 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact 1-day RAS Specialist Discussion Meeting on LSST in London, presented plans for cosmological analysis
Year(s) Of Engagement Activity 2017
 
Description RAS friends talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Outreach presentation to the Friends of the RAS Society, RAS London
Year(s) Of Engagement Activity 2017
 
Description ROE Open Days (2012) 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact engaged with ~100 members of public in discussions and demonstrations on Citizen Science (>1000 visitors total at event)

I was specially mentioned in Open Days feedback for engaging science communication; several visitors declared interest to participate in Citizen Science projects
Year(s) Of Engagement Activity 2012
 
Description ROE Winter Talk (Edinburgh) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact 50 members of public attended, with ample questions and discussion afterwards

several people approached me to thank me for new insights, incl. plan to revive study of astronomy/observations
Year(s) Of Engagement Activity 2013
 
Description Research Festival on "Big Data" 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Other audiences
Results and Impact gave overview of Big Data applications in Astrophysics; highlighted interdisciplinary aspects
Year(s) Of Engagement Activity 2016
 
Description Texas Symposium Cape Town 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Attended International Texas Symposium on Relativistic Astrophysics and presented on weak gravitational lensing
Year(s) Of Engagement Activity 2017