Euclid preparation

LXXXII. Predicting star-forming galaxy scaling relations with the spectral stacking code SpectraPyle

¹ Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna, via Piero Gobetti 93/2, 40129 Bologna, Italy
² INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
³ INAF-IASF Milano, Via Alfonso Corti 12, 20133 Milano, Italy
⁴ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Via Marzolo 8, 35131 Padova, Italy
⁵ INAF-Osservatorio Astronomico di Padova, Via dell’Osservatorio 5, 35122 Padova, Italy
⁶ Department of Physics, Oxford University, Keble Road Oxford, OX1 3RH, UK
⁷ Aix-Marseille Université, CNRS, CNES, LAM, Marseille, France
⁸ Dipartimento di Fisica e Astronomia, Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁹ ESAC/ESA, Camino Bajo del Castillo, s/n., Urb. Villafranca del Castillo, 28692 Villanueva de la Cañada, Madrid, Spain
¹⁰ INAF-Osservatorio Astronomico di Brera, Via Brera 28, 20122 Milano, Italy
¹¹ Minnesota Institute for Astrophysics, University of Minnesota, 116 Church St SE Minneapolis, MN 55455, USA
¹² Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
¹³ INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
¹⁴ Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 München, Germany
¹⁵ INAF-Istituto di Astrofisica e Planetologia Spaziali, via del Fosso del Cavaliere 100, 00100 Roma, Italy
¹⁶ Instituto de Astrofísica de Canarias, E-38205 La Laguna; Universidad de La Laguna, Dpto. Astrofísica, E-38206 La Laguna, Tenerife, Spain
¹⁷ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
¹⁸ INAF-Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34143 Trieste, Italy
¹⁹ School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
²⁰ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
²¹ Dipartimento di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
²² Institute of Physics, Laboratory for Galaxy Evolution, Ecole Polytechnique Fédérale de Lausanne, Observatoire de Sauverny, CH-1290 Versoix, Switzerland
²³ Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
²⁴ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
²⁵ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
²⁶ Univ. Lille, CNRS, Centrale Lille, UMR 9189 CRIStAL, 59000 Lille, France
²⁷ Université Paris-Saclay, CNRS, Institut d’astrophysique spatiale, 91405 Orsay, France
²⁸ Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
²⁹ Université PSL, Observatoire de Paris, Sorbonne Université, CNRS, LERMA, 75014 Paris, France
³⁰ Université Paris-Cité, 5 Rue Thomas Mann, 75013 Paris, France
³¹ School of Mathematics and Physics, University of Surrey, Guildford, Surrey, GU2 7XH, UK
³² IFPU, Institute for Fundamental Physics of the Universe, via Beirut 2, 34151 Trieste, Italy
³³ INFN, Sezione di Trieste, Via Valerio 2, 34127 Trieste TS, Italy
³⁴ SISSA, International School for Advanced Studies, Via Bonomea 265, 34136 Trieste TS, Italy
³⁵ INFN-Sezione di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
³⁶ Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy
³⁷ INFN-Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy
³⁸ Department of Physics “E. Pancini”, University Federico II, Via Cinthia 6, 80126 Napoli, Italy
³⁹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, PT4150-762 Porto, Portugal
⁴⁰ Faculdade de Ciências da Universidade do Porto, Rua do Campo de Alegre, 4150-007 Porto, Portugal
⁴¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁴² Dipartimento di Fisica, Università degli Studi di Torino, Via P. Giuria 1, 10125 Torino, Italy
⁴³ INFN-Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy
⁴⁴ INAF-Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese (TO), Italy
⁴⁵ European Space Agency/ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
⁴⁶ Institute Lorentz, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁴⁷ Leiden Observatory, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
⁴⁸ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Avenida Complutense 40, 28040 Madrid Spain
⁴⁹ Port d’Informació Científica, Campus UAB, C. Albareda s/n, 08193 Bellaterra (Barcelona), Spain
⁵⁰ Institute for Theoretical Particle Physics and Cosmology (TTK), RWTH Aachen University, 52056 Aachen, Germany
⁵¹ INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Italy
⁵² INFN section of Naples, Via Cinthia 6, 80126 Napoli, Italy
⁵³ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive Honolulu, HI, 96822, USA
⁵⁴ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill Edinburgh, EH9 3HJ, UK
⁵⁵ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester, Oxford Road Manchester, M13 9PL, UK
⁵⁶ European Space Agency/ESRIN, Largo Galileo Galilei 1, 00044 Frascati, Roma, Italy
⁵⁷ Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822, Villeurbanne, F-69100, France
⁵⁸ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 08028 Barcelona, Spain
⁵⁹ Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig de Lluís Companys 23, 08010 Barcelona, Spain
⁶⁰ UCB Lyon 1, CNRS/IN2P3, IUF, IP2I Lyon, 4 rue Enrico Fermi, 69622 Villeurbanne, France
⁶¹ Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Edifício C8, Campo Grande, PT1749-016 Lisboa, Portugal
⁶² Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
⁶³ Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290 Versoix, Switzerland
⁶⁴ INFN-Padova, Via Marzolo 8, 35131 Padova, Italy
⁶⁵ Aix-Marseille Université, CNRS/IN2P3, CPPM, Marseille, France
⁶⁶ Space Science Data Center, Italian Space Agency, via del Politecnico snc, 00133 Roma, Italy
⁶⁷ INFN-Bologna, Via Irnerio 46, 40126 Bologna, Italy
⁶⁸ Max Planck Institute for Extraterrestrial Physics, Giessenbachstr. 1, 85748 Garching, Germany
⁶⁹ Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
⁷⁰ INFN-Sezione di Milano, Via Celoria 16, 20133 Milano, Italy
⁷¹ Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, 0315 Oslo, Norway
⁷² Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive Pasadena, CA, 91109, USA
⁷³ Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK
⁷⁴ Felix Hormuth Engineering, Goethestr. 17, 69181 Leimen, Germany
⁷⁵ Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
⁷⁶ Cosmic Dawn Center (DAWN), Denmark
⁷⁷ Institut d’Astrophysique de Paris, UMR 7095, CNRS, and Sorbonne Université, 98 bis boulevard Arago, 75014 Paris, France
⁷⁸ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁷⁹ NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
⁸⁰ Department of Physics and Astronomy, University College London, Gower Street London, WC1E 6BT, UK
⁸¹ Department of Physics and Helsinki Institute of Physics, Gustaf Hällströmin katu 2 University of Helsinki, 00014 Helsinki, Finland
⁸² Université de Genève, Département de Physique Théorique and Centre for Astroparticle Physics, 24 quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
⁸³ Department of Physics, P.O. Box 64 University of Helsinki, 00014 Helsinki, Finland
⁸⁴ Helsinki Institute of Physics, Gustaf Hällströmin katu 2 University of Helsinki, 00014 Helsinki, Finland
⁸⁵ Laboratoire d’etude de l’Univers et des phenomenes eXtremes, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS, 92190 Meudon, France
⁸⁶ SKAO, Jodrell Bank, Lower Withington, Macclesfield, SK11 9FT, UK
⁸⁷ Centre de Calcul de l’IN2P3/CNRS, 21 avenue Pierre de Coubertin, 69627 Villeurbanne Cedex, France
⁸⁸ University of Applied Sciences and Arts of Northwestern Switzerland, School of Computer Science, 5210 Windisch, Switzerland
⁸⁹ Universität Bonn, Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
⁹⁰ INFN-Sezione di Roma, Piazzale Aldo Moro, 2 – c/o Dipartimento di Fisica Edificio G. Marconi, 00185 Roma, Italy
⁹¹ Department of Physics, Institute for Computational Cosmology, Durham University, South Road Durham, DH1 3LE, UK
⁹² Université Paris Cité, CNRS, Astroparticule et Cosmologie, 75013 Paris, France
⁹³ CNRS-UCB International Research Laboratory, Centre Pierre Binétruy, IRL2007, CPB-IN2P3 Berkeley, USA
⁹⁴ University of Applied Sciences and Arts of Northwestern Switzerland, School of Engineering, 5210 Windisch, Switzerland
⁹⁵ Institut d’Astrophysique de Paris, 98bis Boulevard Arago, 75014 Paris, France
⁹⁶ Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
⁹⁷ Telespazio UK S.L. for European Space Agency (ESA), Camino bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo Villanueva de la Cañada, 28692 Madrid, Spain
⁹⁸ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra (Barcelona), Spain
⁹⁹ DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 155, 2200 Copenhagen, Denmark
¹⁰⁰ Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
¹⁰¹ Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
¹⁰² Perimeter Institute for Theoretical Physics, Waterloo, Ontario, N2L 2Y5, Canada
¹⁰³ Centre National d’Etudes Spatiales – Centre spatial de Toulouse, 18 avenue Edouard Belin, 31401 Toulouse Cedex 9, France
¹⁰⁴ Institute of Space Science, Str. Atomistilor, nr. 409 Măgurele Ilfov, 077125, Romania
¹⁰⁵ Consejo Superior de Investigaciones Cientificas, Calle Serrano 117, 28006 Madrid, Spain
¹⁰⁶ Universidad de La Laguna, Dpto. Astrofísica, E-38206 La Laguna, Tenerife, Spain
¹⁰⁷ Institut für Theoretische Physik, University of Heidelberg, Philosophenweg 16, 69120 Heidelberg, Germany
¹⁰⁸ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, CNRS, UPS, CNES, 14 Av. Edouard Belin, 31400 Toulouse, France
¹⁰⁹ Université St Joseph; Faculty of Sciences, Beirut, Lebanon
¹¹⁰ Departamento de Física, FCFM, Universidad de Chile, Blanco Encalada 2008 Santiago, Chile
¹¹¹ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstr. 25/8, 6020 Innsbruck, Austria
¹¹² Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC, 08860 Castelldefels, Barcelona, Spain
¹¹³ Satlantis, University Science Park, Sede Bld 48940 Leioa-Bilbao, Spain
¹¹⁴ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA, 91125, USA
¹¹⁵ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
¹¹⁶ Cosmic Dawn Center (DAWN)
¹¹⁷ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark
¹¹⁸ Universidad Politécnica de Cartagena, Departamento de Electrónica y Tecnología de Computadoras, Plaza del Hospital 1, 30202 Cartagena, Spain
¹¹⁹ Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, Via Giuseppe Saragat 1, 44122 Ferrara, Italy
¹²⁰ Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara, Via Giuseppe Saragat 1, 44122 Ferrara, Italy
¹²¹ INAF, Istituto di Radioastronomia, Via Piero Gobetti 101, 40129 Bologna, Italy
¹²² Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice cedex 4, France
¹²³ Aurora Technology for European Space Agency (ESA), Camino bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
¹²⁴ INAF – Osservatorio Astronomico di Brera, via Emilio Bianchi 46, 23807 Merate, Italy
¹²⁵ INAF-Osservatorio Astronomico di Brera, Via Brera 28, 20122 Milano, Italy, and INFN-Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy
¹²⁶ ICL, Junia, Université Catholique de Lille, LITL, 59000 Lille, France
¹²⁷ ICSC – Centro Nazionale di Ricerca in High Performance Computing, Big Data e Quantum Computing, Via Magnanelli 2 Bologna, Italy
¹²⁸ Instituto de Física Teórica UAM-CSIC, Campus de Cantoblanco, 28049 Madrid, Spain
¹²⁹ CERCA/ISO, Department of Physics, Case Western Reserve University, 10900 Euclid Avenue Cleveland, OH 44106, USA
¹³⁰ Technical University of Munich, TUM School of Natural Sciences, Physics Department, James-Franck-Str. 1, 85748 Garching, Germany
¹³¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
¹³² Laboratoire Univers et Théorie, Observatoire de Paris, Université PSL, Université Paris Cité, CNRS, 92190 Meudon, France
¹³³ Departamento de Física Fundamental. Universidad de Salamanca, Plaza de la Merced s/n, 37008 Salamanca, Spain
¹³⁴ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
¹³⁵ Center for Data-Driven Discovery, Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
¹³⁶ Dipartimento di Fisica – Sezione di Astronomia, Università di Trieste, Via Tiepolo 11, 34131 Trieste, Italy
¹³⁷ California Institute of Technology, 1200 E California Blvd, Pasadena, CA, 91125, USA
¹³⁸ Department of Physics & Astronomy, University of California Irvine, Irvine, CA, 92697, USA
¹³⁹ Departamento Física Aplicada, Universidad Politécnica de Cartagena, Campus Muralla del Mar, 30202 Cartagena, Murcia, Spain
¹⁴⁰ Instituto de Física de Cantabria, Edificio Juan Jordá, Avenida de los Castros, 39005 Santander, Spain
¹⁴¹ INFN, Sezione di Lecce, Via per Arnesano CP-193, 73100 Lecce, Italy
¹⁴² Department of Mathematics and Physics E. De Giorgi, University of Salento, Via per Arnesano CP-I93, 73100 Lecce, Italy
¹⁴³ INAF-Sezione di Lecce, c/o Dipartimento Matematica e Fisica, Via per Arnesano, 73100 Lecce, Italy
¹⁴⁴ CEA Saclay, DFR/IRFU, Service d’Astrophysique, Bat. 709, 91191 Gif-sur-Yvette, France
¹⁴⁵ Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX, UK
¹⁴⁶ Department of Computer Science, Aalto University, PO Box 15400 Espoo, FI-00 076, Finland
¹⁴⁷ Caltech/IPAC, 1200 E. California Blvd. Pasadena, CA, 91125, USA
¹⁴⁸ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), German Centre for Cosmological Lensing (GCCL), 44780 Bochum, Germany
¹⁴⁹ Department of Physics and Astronomy, Vesilinnantie 5, University of Turku, 20014 Turku, Finland
¹⁵⁰ Serco for European Space Agency (ESA), Camino bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
¹⁵¹ ARC Centre of Excellence for Dark Matter Particle Physics, Melbourne, Australia
¹⁵² Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Hawthorn, Victoria, 3122, Australia
¹⁵³ Department of Physics and Astronomy, University of the Western Cape, Bellville, Cape Town, 7535, South Africa
¹⁵⁴ DAMTP, Centre for Mathematical Sciences, Wilberforce Road Cambridge, CB3 0WA, UK
¹⁵⁵ Kavli Institute for Cosmology Cambridge, Madingley Road Cambridge, CB3 0HA, UK
¹⁵⁶ Department of Astrophysics, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
¹⁵⁷ Department of Physics, Centre for Extragalactic Astronomy, Durham University, South Road Durham, DH1 3LE, UK
¹⁵⁸ IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette Cedex, France
¹⁵⁹ Oskar Klein Centre for Cosmoparticle Physics, Department of Physics, Stockholm University, Stockholm, SE-106 91, Sweden
¹⁶⁰ Astrophysics Group, Blackett Laboratory, Imperial College London, London, SW7 2AZ, UK
¹⁶¹ Univ. Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 53 Avenue des Martyrs, 38000 Grenoble, France
¹⁶² Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 2, 00185 Roma, Italy
¹⁶³ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁶⁴ HE Space for European Space Agency (ESA), Camino bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo Villanueva de la Cañada, 28692 Madrid, Spain
¹⁶⁵ INAF – Osservatorio Astronomico d’Abruzzo, Via Maggini, 64100 Teramo, Italy
¹⁶⁶ Theoretical astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 37 Uppsala, Sweden
¹⁶⁷ Mathematical Institute, University of Leiden, Einsteinweg 55, 2333 CA Leiden, The Netherlands
¹⁶⁸ School of Physics & Astronomy, University of Southampton, Highfield Campus, Southampton, SO17 1BJ, UK
¹⁶⁹ Institute of Astronomy, University of Cambridge, Madingley Road Cambridge, CB3 0HA, UK
¹⁷⁰ Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ, 08544, USA
¹⁷¹ Space physics and astronomy research unit, University of Oulu, Pentti Kaiteran katu 1, FI-90014 Oulu, Finland
¹⁷² Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, 10010 New York, NY, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 September 2025
Accepted: 30 November 2025

Abstract

We introduce SpectraPyle, a versatile spectral stacking pipeline developed for the Euclid mission’s NISP spectroscopic surveys, aimed at extracting faint emission lines and spectral features from large galaxy samples in the Wide and Deep Surveys. Designed for computational efficiency and flexible configuration, SpectraPyle supports the processing of extensive datasets critical to Euclid’s non-cosmological science goals. We validated the pipeline using simulated spectra processed to match Euclid’s expected final data quality. Stacking enables robust recovery of key emission lines, including Hα, Hβ, [O III], and [N II], below individual detection limits. However, the measurement of galaxy properties such as star formation rate, dust attenuation, and gas-phase metallicity are biased at stellar mass below log₁₀(M_/ M_⊙)∼9 due to the flux-limited nature of Euclid spectroscopic samples, where spectra below the detection threshold lack reliable redshift measurements, preventing effective stacking. The star formation rate–stellar mass relation of the parent sample is recovered reliably only in the deep survey for log₁₀(M_/ M_⊙)≳10, whereas the metallicity–mass relation is recovered more accurately over a wider mass range. These limitations are caused by the increased fraction of redshift measurement errors at lower masses and fluxes. We examined the impact of residual redshift contaminants that arises from mis-identified emission lines and noise spikes, on stacked spectra. Even after stringent quality selections, low-level contamination (< 6%) has minimal impact on line fluxes due to the systematically weaker emission of contaminants. A percentile-based analysis of stacked spectra provides a sensitive diagnostic for detecting contamination via coherent spurious features at characteristic wavelengths. While our simulations include most instrumental effects, real Euclid data will require a further refinement of contamination mitigation strategies.