TESTDE: Testing the Dark Energy paradigm and measuring neutrino mass with the Dark Energy Survey

TESTDE was a €2.4M project funded by the European Research Council as an Advanced Grant awarded to Prof. Ofer Lahav, which ran from May 2012 to April 2018.

The TESTDE Project is focused on "Testing the Dark Energy Paradigm and Measuring Neutrino Mass with the Dark Energy Survey". It resulted in over 170 publications co-authored by TESTDE members, with around 30 of these papers led by our team.

One of the greatest mysteries in the whole of science is that 70% of the Universe appears to be made of an enigmatic ‘Dark Energy’. A further 25% of the Universe is made from invisible ‘Cold Dark Matter’ that can only be detected through its gravitational effects, with the ordinary atomic matter making up only 5% of the total cosmic budget. These discoveries require a shift in our perception. The TESTDE team has played leadership roles in several large surveys, in particular the $40M international Dark Energy Survey (DES), where Prof. Lahav co-chaired the entire science programme (2006-2016), with 400 scientists from 7 countries.

DES had its first light in September 2012, and the five planned seasons (2013-2018) are now complete. The DES data has been key to exploring the three interlinked TESTDE themes:

1. Combined probes of Dark Energy and Modified Gravity from DES and DESI: Modelling the cross-talk of DES probes and a feasibility study for a spectroscopic follow-up (DESI) which will allow testing modified General Relativity models as alternatives to Dark Energy;
2. Neutrino Masses from Cosmology: Attempting for the first time to measure the as yet unknown neutrino mass from DES, including novel modelling of the non-linear power spectrum;
3. Photometric Redshifts and their impact for cosmic probes: Developing new approaches to photometric redshifts

Project Results

Over the duration of the grant (2012 - 2018) we have made very good progress in all frontiers, resulting in many publications.

We are pleased that the Dark Energy Survey (DES), central to the TESTDE project, has produced high quality data. The DES camera (DECAM) instrument, partly built at UCL, is operating well at the Blanco 4m telescope in Chile. 

Project Highlights

• Based on a combination of the three themes and work by others in the DES collaboration, DES results so far strongly favour a present day universe with Dark Energy in the form of a Cosmological Constant (70%) + Cold Dark Matter (25%) and baryons (5%) in a much better accuracy and precision than previously known from galaxy surveys.
• The Neutrino mass upper limit has been improved, down to 0.26 eV, but not detected yet. This is a major challenge for the DES final analysis.
• An unexpected and exciting spin-off of the TESTDE project is the optical DES camera followup of the LIGO Gravitational Wave Binary Neutron Star (BNS) GW170817. Members of our TESTDE team led a study of the host galaxy NGC4993, proposing that its shell structure may indicate the galaxy merger, with implications for the formation of the BNS.