The statistical era of strong gravitational lensing cosmology

Project Information

LensEra

Grant agreement ID: 945536

DOI

10.3030/945536

EC signature date 3 December 2020

Start date 1 August 2021

End date 31 July 2027

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 794 707,00

EU contribution

€ 1 794 707,00

Coordinated by

UNIVERSITY OF PORTSMOUTH HIGHER EDUCATION CORPORATION
United Kingdom

Periodic Reporting for period 3 - LensEra (The statistical era of strong gravitational lensing cosmology)

Reporting period: 2024-08-01 to 2026-01-31

Summary of the context and overall objectives of the project

The expansion of the Universe is getting faster and we don’t know why. To solve this mystery we are using an effect called gravitational lensing to answer three questions:
- How fast is the Universe currently expanding?
- How does gravity work over astronomical distance scales?
- What is the dominant component of the Universe’s energy budget?

Gravitational lensing occurs when two galaxies are aligned on the sky to about 1/3600 of a degree. The mass of the foreground galaxy warps spacetime and deflects the light from the background galaxy as it passes. Despite being a powerful cosmological probe for matter distribution, strong gravitational lensing is hamstrung by the small number of lensing systems: only a few hundred systems are known. The EU-funded LensEra project plans to combine machine learning, citizen science and automated lens modelling to build an engine to find new lensing systems in the Large Synoptic Survey Telescope data in Chile. Analysis of subsets of lens populations will enable us to explore the most profound questions of our Universe, including the nature of dark matter and the measurement of dark energy’s equation of state.


These are the two main objectives of LensEra:
1. Discovery of 30,000 new lenses using machine learning and citizen science.
2. Development of new cosmological measurements with strong lenses, enabling competitive constraints on the current expansion rate (H0 to 1% precision), the properties of dark energy (w to 4%) and the validity of General Relativity (the amount of spatial curvature produced per unit mass to 1%, measured over the scales of galaxies).

Attached are two images of recently discovered lensed SNe where LensEra scientists played a role: one lensed by a small galaxy and another by a massive cluster of galaxies.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

On 1. We have investigated how human experts find new lenses, we have searched for lensed SNe in ZTF archives and we have done substantial preparatory work for LSST and Euclid. We have recently received the first 40 square degrees of Euclid data and have commenced a search, finding several candidates in the first 1.5 square degrees searched. This suggests that the full 15000 sq degree survey should indeed contain the expected 100,000 lenses forecast in Collett 2015.

On 2. We have shown how to use lensed SNe to constrain systematics in lens modelling enabling a 1.5% precision H0 measurement with LSST. We have demonstrated that large samples of lenses are viable probes of dark energy and we have built new lens modelling codes to do the analysis. We have tested the analysis on a unique triple source plane lens, allowing us to test systematics and to constrain w (dark matter work published, dark energy constraint in prep). We are integrating kinematic modelling into the lens modelling code to enable new GR tests, and have found an extremely powerful new lens for this science in early Euclid data (in prep). We have also developed new GPU accelerated lens modelling code that will allow us to cope with the large sample of lenses that LensEra will discover.

We have written 14 publications so far on our work:
Weisenbach, L., et al. (2024) "How to Break the Mass Sheet Degeneracy with the Lightcurves of Microlensed Type Ia Supernovae", arXiv e-prints
Ballard, D. J., et al. (2024) "Gravitational imaging through a triple source plane lens: revisiting the ΛCDM-defying dark subhalo in SDSSJ0946+1006", Monthly Notices of the Royal Astronomical Society
Turner, H. C., et al. (2024) "Two-dimensional kinematics and dynamical modelling of the 'Jackpot' gravitational lens from deep MUSE observations", Monthly Notices of the Royal Astronomical Society
Li, T., et al. (2024) "Cosmology from large populations of galaxy-galaxy strong gravitational lenses", Monthly Notices of the Royal Astronomical Society
Sainz de Murieta, A., et al. (2023) "Lensed Type Ia supernovae in light of SN Zwicky and iPTF16geu", Monthly Notices of the Royal Astronomical Society
Magee, M. R., et al. (2023) "A search for gravitationally lensed supernovae within the Zwicky transient facility public survey", Monthly Notices of the Royal Astronomical Society
Rojas, K., et al. (2023) "The impact of human expert visual inspection on the discovery of strong gravitational lenses", Monthly Notices of the Royal Astronomical Society
Goobar, A., et al. (2023) "Uncovering a population of gravitational lens galaxies with magnified standard candle SN Zwicky", Nature Astronomy
Sharma, D., et al. (2023) "Testing cosmology with double source lensing", Journal of Cosmology and Astroparticle Physics
Collett, T. E., et al. (2023) "The 4MOST Strong Lensing Spectroscopic Legacy Survey (4SLSLS)", The Messenger
Graham, M. L., et al. (2023) "Deep drilling in the time domain with DECam: survey characterization", Monthly Notices of the Royal Astronomical Society
Shajib, A. J., et al. (2022) "LensingETC: A Tool to Optimize Multifilter Imaging Campaigns of Galaxy-scale Strong Lensing Systems", The Astrophysical Journal
Tran, K.-V. H., et al. (2022) "The AGEL Survey: Spectroscopic Confirmation of Strong Gravitational Lenses in the DES and DECaLS Fields Selected Using Convolutional Neural Networks", The Astronomical Journal
Magee et al. (2021) "The detection efficiency of Type Ia supernovae from the Zwicky Transient Facility: limits on the intrinsic rate of early flux excesses" Monthly Notices of the Royal Astronomical Society

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We are now working on discovering the lenses in Euclid and LSST, and measuring cosmological parameters with them. We are working hard to get ready for our 4MOST spectroscopic followup campaign which will deliver redshifts for the lenses we will discover. These redshifts are critical for a range of science beyond LensEra. Never before have such large samples of lenses been discovered, nor has a spetroscopic campaign of this magnitude been conducted for lens followup. Once we have this data in hand we will be able to measure the current expansion rate of the Universe the properties of dark energy , and the validity of General Relativity in astronomical length scales.

A new supernova lensed by a cluster of galaxies (From Pierel et al 2024)

A new supernova lensed by a very low mass galaxy (From Goobar et al 2023)