Journal
ASTRONOMY & ASTROPHYSICS
Volume 647, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/202040237
Keywords
dark energy; galaxies: distances and redshifts; methods: statistical
Categories
Funding
- French Agence Nationale de la Recherche
- CNES fellowship
- Heisenberg grant of the Deutsche Forschungsgemeinschaft [Hi 1495/5-1]
- ERC Consolidator Grant [770935]
- European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant [896225]
- Centre National d'Etudes Spatiales (CNES)
- ESO Telescopes at the La Silla Paranal Observatory under programme [177.A-3016, 177.A-3017, 177.A-3018, 179.A2004]
- Deutsche Forschungsgemeinschaft
- NOVA
- University of Padova
- University Federico II (Naples)
- PRIN MIUR2015 Cosmology and Fundamental Physics: Illuminating the Dark Universe with Euclid
- European Space Agency
- Agenzia Spaziale Italiana
- Belgian Science Policy
- Canadian Euclid Consortium
- Centre National d'Etudes Spatiales
- Danish Space Research Institute
- Fundacao para a Ciencia e a Tecnologia
- Ministerio de Economia y Competitividad
- National Aeronautics and Space Administration
- Netherlandse Onderzoekschool Voor Astronomie
- Norwegian Space Agency
- Romanian Space Agency
- State Secretariat for Education, Research and Innovation (SERI) at the Swiss Space Office (SSO)
- United Kingdom Space Agency
- ERC
- NWO-M grants
- Target
- Academy of Finland
- Deutsches Zentrum fur Luft-und Raumfahrt
- Marie Curie Actions (MSCA) [896225] Funding Source: Marie Curie Actions (MSCA)
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The study explores methods for constraining the dark energy equation of state by measuring the mean redshift z of galaxies in wide-field imaging surveys. Comparing two standard approaches, it finds that direct calibration of z requires a highly pure spectroscopic sample, while the zPDF approach depends on deep imaging data and is less sensitive to spectroscopic redshift failures.
The analysis of weak gravitational lensing in wide-field imaging surveys is considered to be a major cosmological probe of dark energy. Our capacity to constrain the dark energy equation of state relies on an accurate knowledge of the galaxy mean redshift z. We investigate the possibility of measuring z with an accuracy better than 0.002 (1+z) in ten tomographic bins spanning the redshift interval 0.2<2.2, the requirements for the cosmic shear analysis of Euclid. We implement a sufficiently realistic simulation in order to understand the advantages and complementarity, as well as the shortcomings, of two standard approaches: the direct calibration of z with a dedicated spectroscopic sample and the combination of the photometric redshift probability distribution functions (zPDFs) of individual galaxies. We base our study on the Horizon-AGN hydrodynamical simulation, which we analyse with a standard galaxy spectral energy distribution template-fitting code. Such a procedure produces photometric redshifts with realistic biases, precisions, and failure rates. We find that the current Euclid design for direct calibration is sufficiently robust to reach the requirement on the mean redshift, provided that the purity level of the spectroscopic sample is maintained at an extremely high level of > 99.8%. The zPDF approach can also be successful if the zPDF is de-biased using a spectroscopic training sample. This approach requires deep imaging data but is weakly sensitive to spectroscopic redshift failures in the training sample. We improve the de-biasing method and confirm our finding by applying it to real-world weak-lensing datasets (COSMOS and KiDS+VIKING-450).
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