Modeling submillimeter galaxies in cosmological simulations: Contribution to the cosmic star formation density and predictions for future surveys

¹ Universidad Andrés Bello, Facultad de Ciencias Exactas, Departamento de Física y Astronomía, Instituto de Astrofísica, Fernández Concha 700, Las Condes, Santiago RM, Chile
² Departamento de Física, Universidad Técnica Federico Santa María, Avenida Vicuña Mackenna 3939, San Joaquín, Santiago, Chile
³ Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907, USA
⁴ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
⁵ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
⁶ Lorentz Institute for Theoretical Physics, Leiden University, PO box 9506 2300 RA Leiden, The Netherlands
⁷ Physics and Astronomy Department, Rutgers, The State University, Piscataway, NJ 08854, USA
⁸ Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
⁹ SNU Astronomy Research Center, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
¹⁰ Australian Astronomical Optics – Macquarie University, 105 Delhi Road, North Ryde, NSW 2113, Australia
¹¹ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
¹² Korea Institute for Advanced Study, 85 Hoegi-ro, Dongdaemun-gu Seoul 02455, Republic of Korea
¹³ Instituto de Astronomía Teórica y Experimental (IATE), CONICET-UNC, Laprida 854, X500BGR Córdoba, Argentina

^⋆ Corresponding authors: ankit4physics@gmail.com; maria.artale@unab.cl

Received: 31 January 2025
Accepted: 21 April 2025

Abstract

Context. Submillimeter galaxies (SMGs) constitute a key population of bright star-forming galaxies at high-redshift. These galaxies challenge galaxy formation models, particularly regarding the reproduction of their observed number counts and redshift distributions. Furthermore, although SMGs contribute significantly to the cosmic star formation rate density (SFRD), their precise role remains uncertain. Upcoming surveys, such as the Ultra Deep Survey with the TolTEC camera, are expected to offer valuable insights into SMG properties and their broader impact in the Universe.

Aims. Robust modeling of SMGs in a cosmological representative volume is necessary to investigate their nature in preparation for next-generation submillimeter surveys. Here, we test different parametric models for SMGs in large-volume hydrodynamical simulations, assess their contribution to the SFRD, and build expectations for future submillimeter surveys.

Methods. We implement and test parametric relations derived from radiative transfer calculations across three cosmological simulation suites: EAGLE, IllustrisTNG, and FLAMINGO. We place particular emphasis on the FLAMINGO simulations due to their large volume and robust statistical sampling of SMGs. Based on the model that best reproduces observational number counts, we forecast submillimeter fluxes within the simulations, analyze the properties of SMGs, and evaluate their evolution over cosmic time.

Results. Our results show that the FLAMINGO simulation reproduces the observed redshift distribution and source number counts of SMGs without requiring a top-heavy initial mass function. On the other hand, the EAGLE and IllustrisTNG simulations show a deficit of bright SMGs. We find that SMGs with S₈₅₀ > 1 mJy contribute up to ∼27% of the cosmic SFRD at z ∼ 2.6 in the FLAMINGO simulation, which is consistent with recent observations. Flux density functions reveal a rise in SMG abundance from z = 6 to z = 2.5 that is followed by a sharp decline in the number of brighter SMGs from z = 2.5 to z = 0. Leveraging the SMG population in FLAMINGO, we forecast that the TolTEC UDS will detect ∼80 000 sources over 0.8 deg² at 1.1 mm (at the 4σ detection limit), capturing about 50% of the cosmic SFRD at z ∼ 2.5.