DELPHI: a framework to study Dark Matter and the emergence of galaxies in the epoch of reionization

Project Information

DELPHI

Grant agreement ID: 717001

DOI

10.3030/717001

Project closed

EC signature date 17 January 2017

Start date 1 March 2017

End date 28 February 2022

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 500 000,00

EU contribution

€ 1 500 000,00

Coordinated by

RIJKSUNIVERSITEIT GRONINGEN
Netherlands

Periodic Reporting for period 4 - DELPHI (DELPHI: a framework to study Dark Matter and the emergence of galaxies in the epoch of reionization)

Reporting period: 2021-09-01 to 2022-02-28

Summary of the context and overall objectives of the project

Our Universe started as a dark featureless sea of hydrogen, helium, and dark matter of unknown composition about 13 and a half billion years ago. The earliest galaxies lit up the Universe with pinpricks of light, ushering in the era of ‘cosmic dawn’. These galaxies represent the primary building blocks of all subsequent galaxies and the sources of the first (hydrogen ionizing) photons that could break apart the hydrogen atoms suffusing all of space, starting the process of ‘cosmic reionization’. By virtue of being the smallest bound structures in the early Universe, these galaxies also provide an excellent testbed for models wherein Dark Matter is composed of warm, fast moving particles as opposed to the sluggish heavy particles used in the standard Cold Dark Matter paradigm.

Exploiting the power of the latest cosmological simulations as well as a semi-analytical model firmly rooted in first principles, DELPHI has aimed at building a coherent and predictive model to answer three of the key outstanding questions in physical cosmology:
- how did the interlinked processes of galaxy formation and reionization drive each other?
- what were the physical properties of early galaxies and how have they evolved through time to give rise to the galaxy properties we see today?
- what is the nature (mass) of the mysterious Dark Matter that makes up 80% of the matter content in the Universe?

The timescale of the ERC has represented an excellent opportunity for progress on these fundamental questions: observations with cutting-edge instruments (e.g. the Hubble and Subaru telescopes) are providing the first tantalising glimpses of early galaxies assembling in an infant Universe, required to pin down theoretical models. The realistic results obtained by DELPHI are also proving vital in determining survey strategies and exploiting synergies between forthcoming key state-of-the-art instruments such as the European-Extremely Large Telescope, the James Webb Space Telescope and the Square Kilometre Array.

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

The project has now been completed. Given my leadership in the field of early galaxy formation, I was invited to write a review for the prestigious Physics Reports [1].

Science Objective A:
WPA1: We have recently submitted a paper on inferring the escape fractions [2]. We have published a proof-of-concept paper to highlight the observability of different escape-fraction scenarios with the Square Kilometre Array [3] and JWST [4].
WPA2: We have run this ASTRAEUS framework for a variety of reionization feedback scenarios to study the galaxy-reionization interplay [5], the key reionization sources [6], the star formation histories of early galaxies [7] and black hole physics [8,9,10]. We have also studied the observability of the 21cm bispectrum with the SKA [11] and 21cm-galaxy correlations for the Astro2020 Decadal survey [12].
WPA3: We have now identified Lyman Alpha Emitters in the Astraeus framework [13]. Our model has also been used to make predictions for the brightness temperature of the IGM using the Millimetre Wave Array [14]. The Astraeus framework has also been used to quantify the cosmic variance expected for forthcoming observations [15]. Finally, going beyond the original plan, our models have also been used to study the impact of Black Hole feedback on the luminosity and stellar mass assembly of high-redshift galaxies [16].

Science objective B:
WPB1: We have fully coupled our semi-analytic galaxy formation model (DELPHI) with a model to track the emergence of dust and metals in early galaxies over an unprecedented mass range [17]. This is being used to interpret the key results from cutting-edge ALMA large programs, including those from REBELS [18].
WPB2: We have included the latest metal yields into the Astraeus framework to track the emergence and evolution of metallicity scaling relations in the first billion years [19].
WPB3: We have used dust in two different models (Astraeus and Delphi) to show their effects on both the star forming and black hole population [10] as well as forming the basis for observing dusty early galaxies [18].

Science objective C:
WPC1-2: During the ERC, we have significantly extended our framework for galaxy formation in multiple DM cosmologies [20] to study their impact on reionziation and its observability [21]
WPC3: In 2017 and 2018, new observations offered an excellent opportunity to use the DELPHI semi-analytic model to put constraints on the warm dark matter particle mass and definitely rule out <3keV warm dark matter [22, 23, 24].

The results of this work have been published in 42 peer-reviewed papers and 8 white papers. We have also been a part of 6 observational campaigns (for both HST and JWST) as a result of out theoretical expertise. Finally, the results have been disseminated in 43 talks in international meetings (a further 6 were postponed/cancelled due to Covid-19), 38 colloquia/seminars in various international departments and through the group members organising 10 conferences (6 as SOC; 4 as Chair). We have also delivered a total of 6 outreach lectures.

Key publications:
[1] Dayal et al., 2018, Physics Reports, Volume 780, p. 1-64
[2] Bremer et al., 2022, submitted to MNRAS.
[3] Seiler et al., 2019, MNRAS, 487, 5739
[4] Choudhury & Dayal, MNRAS, 2019, 482, 19
[5] Hutter et al., 2021, MNRAS, 503, 3698
[6] Hutter et al., 2021, MNRAS, 506, 215
[7] Legrand et al., 2021, MNRAS, 509, 595
[8] Dayal et al., 2019, MNRAS, 486, 2336
[9] Piana et al., 2021, MNRAS, 500, 2146
[10] Trebitsch et al., 2022, arXiv: 2202.02337
[11] Hutter et al., 2020, MNRAS, 492, 653
[12] Hutter et al., 2019, BAAS, Vol. 51, Issue 57, id. 360
[13] Hutter et al., 2022, submitted to MNRAS
[14] Trott et al., 2021, MNRAS, 507, 772
[15] Ucci et al., 2021, MNRAS, 506, 202
[16] Piana et al., 2022, MNRAS, 510, 5661
[17] Dayal et al., 2022, MNRAS, 512, 989
[18] Bouwens et al, 2022, ApJ, 931, 160
[19] Ucci et al., 2021, submitted to MNRAS, arXiv:2112.02115
[20] Dayal et al., 2015, ApJ, 806, 67D
[21] Dayal et al., 2017, ApJ, 836, 16
[22] Bremer et al., 2018, MNRAS, 477, 2154
[23] Dayal et al., 2017, MNRAS, 472, 4414
[24] Chatterjee et al, 2019, MNRAS, 487, 3560

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)

Novel and unconventional methodologies, yielding beyond-state-of-the-art results, have been developed for each science objective of the DELPHI project as now detailed.
Science Objective A: We are using custom-built large volume (230 Megaparsec), high-resolution (56 billion particles) N-body CDM simulations that allow, for the first time, to probe galaxies all the way from the key reionization sources (~10^8 solar mass) to the rarest high-mass systems observed (~ 10^12 solar mass). The framework resulting from these goes significantly beyond the current-state-of-the-art in the filed, both in terms of the mass scales explored as well as the physics implemented for reionization feedback.
Science objective B: We have included dust and metallicity prescriptions into the framework developed in Science Objective A. This is the first framework modelling galaxy formation against a coherent reionization background that includes all the key prescriptions for dust formation.
Science objective C: In work package C3, we have used the metal enrichment of the IGM to rule out very light (~2 keV) warm dark matter models and the EDGES signal to rule out <3keV warm dark matter.

delphi-diagram-final-04.jpg