Euclid: Forecasting the number counts of bright line emitters in the Euclid Wide Survey and Euclid Deep fields
Abstract
The Euclid mission will revolutionize our understanding of the visible Universe by collecting images and spectra of millions of galaxies across cosmic time and environments. Here, we forecast the number counts of galaxies emitting [OII], H\b{eta}, [OIII], Hα and Pa\b{eta} lines in the Euclid Wide Survey (EWS) and Deep Survey (EDS). We compare predictions from different models, including semi-analytic models and empirical scaling relations. We then simulate spectra for galaxies in the MAMBO lightcone using FastSpec, designed to rapidly generate one-dimensional spectra as observed by Euclid. We process these simulated spectra with the official Euclid spectroscopic pipeline to recover redshifts and line fluxes and derive expected counts. Predictions for Hα+[NII] emitters are broadly consistent across mocks and with existing observations. In the EWS, relative RMS scatter among mock predictions for integrated counts is approximately 19% for Hα+[NII], 44% for [OII] and 41% for [OIII], reflecting greater model dependence for oxygen-line forecasts. After accounting for flux losses and redshift misidentification, corrected flux measurements recover most intrinsic line counts, especially in the EDS. From the MAMBO-based FastSpec simulations, we predict that Euclid will detect about 42 million Hα emitters in the EWS and 1.7 million in the EDS. The same simulations predict approximately 0.5 and 0.8 million [OII] and [OIII] emitters, respectively, in the EDS, and about 1.3 and 7.5 million in the EWS. These non-Hα forecasts remain subject to substantial model-dependent uncertainties, as shown by scatter among the different mocks. These samples will be instrumental in pushing large-scale structure and baryon acoustic oscillation studies beyond redshift z~2, extending Euclid cosmological and galaxy evolution studies beyond what is achievable with Hα alone.
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BibTeX
@misc{collaboration2026euclid,
title = {{Euclid: Forecasting the number counts of bright line emitters in the Euclid Wide Survey and Euclid Deep fields}},
author = {Euclid Collaboration and P. Cassata and S. Quai and C. Mancini and L. Pozzetti and L. Gabarra and M. Talia and L. Bisigello and M. Bolzonella and G. De Lucia and A. Enia and A. Feltre and F. Fontanot and M. Hirschmann and V. Le Brun and M. Moresco and M. Scodeggio and L. Scharré and M. Siudek and D. Vergani and G. Zamorani and O. Cucciati and N. Aghanim and B. Altieri and S. Andreon and N. Auricchio and C. Baccigalupi and M. Baldi and S. Bardelli and P. Battaglia and A. Biviano and E. Branchini and M. Brescia and S. Camera and G. Cañas-Herrera and V. Capobianco and C. Carbone and J. Carretero and M. Castellano and G. Castignani and S. Cavuoti and A. Cimatti and C. Colodro-Conde and G. Congedo and L. Conversi and Y. Copin and F. Courbin and H. M. Courtois and H. Degaudenzi and S. de la Torre and H. Dole and F. Dubath and X. Dupac and A. Ealet and S. Escoffier and M. Farina and R. Farinelli and F. Faustini and S. Ferriol and P. Fosalba},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.05484},
eprint = {2611.05484},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.05484},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Euclid: Forecasting the number counts of bright line emitters in the Euclid Wide Survey and Euclid Deep fields
AU - Euclid Collaboration
AU - P. Cassata
AU - S. Quai
AU - C. Mancini
AU - L. Pozzetti
AU - L. Gabarra
AU - M. Talia
AU - L. Bisigello
AU - M. Bolzonella
AU - G. De Lucia
AU - A. Enia
AU - A. Feltre
AU - F. Fontanot
AU - M. Hirschmann
AU - V. Le Brun
AU - M. Moresco
AU - M. Scodeggio
AU - L. Scharré
AU - M. Siudek
AU - D. Vergani
AU - G. Zamorani
AU - O. Cucciati
AU - N. Aghanim
AU - B. Altieri
AU - S. Andreon
AU - N. Auricchio
AU - C. Baccigalupi
AU - M. Baldi
AU - S. Bardelli
AU - P. Battaglia
AU - A. Biviano
AU - E. Branchini
AU - M. Brescia
AU - S. Camera
AU - G. Cañas-Herrera
AU - V. Capobianco
AU - C. Carbone
AU - J. Carretero
AU - M. Castellano
AU - G. Castignani
AU - S. Cavuoti
AU - A. Cimatti
AU - C. Colodro-Conde
AU - G. Congedo
AU - L. Conversi
AU - Y. Copin
AU - F. Courbin
AU - H. M. Courtois
AU - H. Degaudenzi
AU - S. de la Torre
AU - H. Dole
AU - F. Dubath
AU - X. Dupac
AU - A. Ealet
AU - S. Escoffier
AU - M. Farina
AU - R. Farinelli
AU - F. Faustini
AU - S. Ferriol
AU - P. Fosalba
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2611.05484
UR - https://arxiv.org/abs/2611.05484
AB - The Euclid mission will revolutionize our understanding of the visible Universe by collecting images and spectra of millions of galaxies across cosmic time and environments. Here, we forecast the number counts of galaxies emitting [OII], H\b{eta}, [OIII], Hα and Pa\b{eta} lines in the Euclid Wide Survey (EWS) and Deep Survey (EDS). We compare predictions from different models, including semi-analytic models and empirical scaling relations. We then simulate spectra for galaxies in the MAMBO lightcone using FastSpec, designed to rapidly generate one-dimensional spectra as observed by Euclid. We process these simulated spectra with the official Euclid spectroscopic pipeline to recover redshifts and line fluxes and derive expected counts. Predictions for Hα+[NII] emitters are broadly consistent across mocks and with existing observations. In the EWS, relative RMS scatter among mock predictions for integrated counts is approximately 19% for Hα+[NII], 44% for [OII] and 41% for [OIII], reflecting greater model dependence for oxygen-line forecasts. After accounting for flux losses and redshift misidentification, corrected flux measurements recover most intrinsic line counts, especially in the EDS. From the MAMBO-based FastSpec simulations, we predict that Euclid will detect about 42 million Hα emitters in the EWS and 1.7 million in the EDS. The same simulations predict approximately 0.5 and 0.8 million [OII] and [OIII] emitters, respectively, in the EDS, and about 1.3 and 7.5 million in the EWS. These non-Hα forecasts remain subject to substantial model-dependent uncertainties, as shown by scatter among the different mocks. These samples will be instrumental in pushing large-scale structure and baryon acoustic oscillation studies beyond redshift z~2, extending Euclid cosmological and galaxy evolution studies beyond what is achievable with Hα alone.
ER -