Advancing weak lensing and intrinsic galaxy alignment studies into the era of precision cosmology
Lead Research Organisation:
University of Edinburgh
Department Name: Sch of 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.
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.
Organisations
- University of Edinburgh (Lead Research Organisation)
- European Southern Observatory (ESO) (Collaboration)
- UK Space Agency (Collaboration)
- LSST Corporation (Collaboration)
- Dark Energy Survey (DES) (Collaboration)
- Autonomous University of Barcelona (UAB) (Collaboration)
- University College London (Fellow)
People |
ORCID iD |
| Benjamin Joachimi (Principal Investigator / Fellow) |
Publications
Amon A
(2018)
KiDS-i-800: comparing weak gravitational lensing measurements from same-sky surveys
in Monthly Notices of the Royal Astronomical Society
Asgari Marika
(2016)
Flat-Sky Pseudo-Cls Analysis for Weak Gravitational Lensing
in ArXiv e-prints
Clerkin L
(2017)
Testing the lognormality of the galaxy and weak lensing convergence distributions from Dark Energy Survey maps
in Monthly Notices of the Royal Astronomical Society
De Jong J
(2015)
The first and second data releases of the Kilo-Degree Survey
in Astronomy & Astrophysics
Duncan C
(2014)
On the complementarity of galaxy clustering with cosmic shear and flux magnification
in Monthly Notices of the Royal Astronomical Society
Duncan CA
(2016)
Cluster mass profile reconstruction with size and flux magnification on the HST STAGES survey.
in Monthly notices of the Royal Astronomical Society
Hildebrandt H
(2017)
KiDS-450: cosmological parameter constraints from tomographic weak gravitational lensing
in Monthly Notices of the Royal Astronomical Society
Hildebrandt H
(2016)
RCSLenS: The Red Cluster Sequence Lensing Survey
in Monthly Notices of the Royal Astronomical Society
Joachimi B
(2015)
Galaxy Alignments: An Overview
in Space Science Reviews
Joachimi B
(2015)
Detection of spatial correlations of Fundamental Plane residuals, and cosmological implications
in Monthly Notices of the Royal Astronomical Society
Joachimi B
(2017)
Non-linear shrinkage estimation of large-scale structure covariance
in Monthly Notices of the Royal Astronomical Society: Letters
Joachimi B
(2013)
Intrinsic galaxy shapes and alignments - II. Modelling the intrinsic alignment contamination of weak lensing surveys
in Monthly Notices of the Royal Astronomical Society
Joachimi B
(2013)
Intrinsic galaxy shapes and alignments - I. Measuring and modelling COSMOS intrinsic galaxy ellipticities
in Monthly Notices of the Royal Astronomical Society
Joachimi B.
(2016)
Euclid - an ESA Medium Class Mission
in Multi-Object Spectroscopy in the Next Decade: Big Questions, Large Surveys, and Wide Fields
Joudaki S
(2017)
CFHTLenS revisited: assessing concordance with Planck including astrophysical systematics
in Monthly Notices of the Royal Astronomical Society
Joudaki Shahab
(2016)
CFHTLenS revisited: assessing concordance with Planck including astrophysical systematics
in ArXiv e-prints
Joudaki Shahab
(2016)
KiDS-450: Testing extensions to the standard cosmological model
in ArXiv e-prints
Kiessling A
(2015)
Galaxy Alignments: Theory, Modelling & Simulations
in Space Science Reviews
Kirk D
(2015)
Galaxy Alignments: Observations and Impact on Cosmology
in Space Science Reviews
Kuijken K
(2015)
Gravitational lensing analysis of the Kilo-Degree Survey
in Monthly Notices of the Royal Astronomical Society
Köhlinger F
(2015)
A direct measurement of tomographic lensing power spectra from CFHTLenS
in Monthly Notices of the Royal Astronomical Society
Köhlinger F
(2017)
KiDS-450: the tomographic weak lensing power spectrum and constraints on cosmological parameters
in Monthly Notices of the Royal Astronomical Society
Schrabback T
(2015)
CFHTLenS: weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment
in Monthly Notices of the Royal Astronomical Society
Schuhmann R
(2016)
Gaussianization for fast and accurate inference from cosmological data
in Monthly Notices of the Royal Astronomical Society
Semboloni E
(2013)
On the shear estimation bias induced by the spatial variation of colour across galaxy profiles
in Monthly Notices of the Royal Astronomical Society
Shi X
(2014)
How well do third-order aperture mass statistics separate E- and B-modes?
in Astronomy & Astrophysics
Sifón C
(2015)
The masses of satellites in GAMA galaxy groups from 100 square degrees of KiDS weak lensing data
in Monthly Notices of the Royal Astronomical Society
Simpson F
(2015)
Enhancing the cosmic shear power spectrum
in Monthly Notices of the Royal Astronomical Society
Soo J
(2018)
Morpho-z: improving photometric redshifts with galaxy morphology
in Monthly Notices of the Royal Astronomical Society
Taylor A
(2013)
Putting the precision in precision cosmology: How accurate should your data covariance matrix be?
in Monthly Notices of the Royal Astronomical Society
Taylor A
(2014)
Estimating cosmological parameter covariance
in Monthly Notices of the Royal Astronomical Society
Van Uitert E
(2016)
Weak-lensing-inferred scaling relations of galaxy clusters in the RCS2: mass-richness, mass-concentration, mass-bias, and more
in Astronomy & Astrophysics
Van Uitert E
(2016)
The stellar-to-halo mass relation of GAMA galaxies from 100 deg 2 of KiDS weak lensing data
in Monthly Notices of the Royal Astronomical Society
Van Uitert E
(2018)
KiDS+GAMA: cosmology constraints from a joint analysis of cosmic shear, galaxy-galaxy lensing, and angular clustering
in Monthly Notices of the Royal Astronomical Society
Van Uitert E
(2017)
Halo ellipticity of GAMA galaxy groups from KiDS weak lensing
in Monthly Notices of the Royal Astronomical Society
Van Uitert Edo
(2016)
Halo ellipticity of GAMA galaxy groups from KiDS weak lensing
in ArXiv e-prints
Van Uitert Edo
(2017)
Intrinsic alignment of redMaPPer clusters: cluster shape - matter density correlation
in ArXiv e-prints
Van Uitert Edo
(2016)
The stellar-to-halo mass relation of GAMA galaxies from 100 square degrees of KiDS weak lensing data
in ArXiv e-prints
Viola M
(2015)
Dark matter halo properties of GAMA galaxy groups from 100 square degrees of KiDS weak lensing data
in Monthly Notices of the Royal Astronomical Society
Viola M
(2014)
On the probability distributions of ellipticity
in Monthly Notices of the Royal Astronomical Society
Xavier H
(2016)
Improving lognormal models for cosmological fields
in Monthly Notices of the Royal Astronomical Society
Xavier Henrique S.
(2016)
FLASK: Full-sky Lognormal Astro-fields Simulation Kit
in Astrophysics Source Code Library
| 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 analysis of galaxy clustering and gravitational lensing to constrain 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 |
| 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 | Charity/Non Profit |
| 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 | Professional Practitioners |
| 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 |