Star formation at z ∼ 0.9 from the OTELO survey: A comprehensive view combining deep optical spectroscopy and infrared data

¹ Escuela Superior de Ingeniería, Ciencia y Tecnología, UNIE Universidad, Arapiles 14, 28015, Madrid, Spain
² Asociación Astrofísica para la Promoción de la Investigación, Instrumentación y su Desarrollo, ASPID, E-38205, La Laguna, Tenerife, Spain
³ Departamento de Física de la Tierra y Astrofísica, Instituto de Física de Partículas y del Cosmos, IPARCOS. Universidad Complutense de Madrid, E-28040, Madrid, Spain
⁴ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada, Spain
⁵ ISDEFE for European Space Astronomy Centre (ESAC)/ESA, P.O. Box 78, E-28690, Villanueva de la Cañada, Madrid, Spain
⁶ Instituto de Astrofísica de Canarias (IAC), E-38200, La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna (ULL), E-38205, La Laguna, Tenerife, Spain
⁸ Instituto de Radioastronomía Milimétrica (IRAM), Av. Divina Pastora 7, Núcleo Central, E-18012, Granada, Spain
⁹ Astronomical Observatory Institute, Faculty of Physics and Astronomy, Adam Mickiewicz University, ul. Słoneczna 36, 60-286, Poznań, Poland
¹⁰ Instituto de Astrofísica de Andalucía, CSIC, E-18080, Granada, Spain
¹¹ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264, 04510, Ciudad de México, Mexico
¹² Instituto de Física de Cantabria (CSIC-Universidad de Cantabria), E-39005, Santander, Spain
¹³ Fundación Galileo Galilei – INAF, 38712, Breña Baja, Tenerife, Spain
¹⁴ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ, UK

^★ Corresponding author.

Received: 15 July 2025
Accepted: 16 March 2026

Abstract

Aims. We aim to quantify the star formation rate (SFR) from deep optical spectroscopic data and far-infrared (FIR) photometry from a sample of galaxies at z ∼ 0.9 from the OTELO survey and compare the activity estimated by optical tracers and FIR emission.

Methods. We used the multi-wavelength OTELO catalogue to construct a sample of FIR sources. We identified and separated galaxies with active nuclei and derived the physical properties of the rest. We analysed their spectral energy distribution, obtaining estimates for stellar mass, dust attenuation, luminosity, and SFR based on infrared luminosity. We also studied Hβ and [O III] λ4959,5007 emission-line galaxies without significant FIR emission from previous works. This approach allowed us to perform a comparative analysis among the SFR obtained through different calibrators, in particular Hβ presented in a previous work

Results. We find that FIR-based SFR estimates uncover a significant fraction of hidden star formation. We determined that the SFR density obtained from the FIR emission is three times larger than that obtained from only emission-line sources. Likely related to the fact that each SFR tracer provides insight into star formation over different timescales, we suggest that such indicators are also more or less suited for different galaxy populations. Specifically, while optical emission lines effectively trace star formation in lower-mass galaxies, FIR-derived SFRs provide a more reliable measure in massive dust-rich systems. By accounting for both optically visible and obscured star formation, we provide a more comprehensive view of the star-forming main sequence at z ∼ 0.9 and reinforce the importance of infrared tracers in studying galaxy evolution.