{"day":"01","acknowledgement":"This research was supported in part by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. This research was supported in part by The Dr Albert Shimmins Fund through the Albert Shimmins Postgraduate Writing Up Award (University of Melbourne). This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–03127 for JWST. These observations are associated with programmes JWST-ERS-1324, JWST-GO-2561, and JWST-DDT-2756. BV and PW acknowledge support from the INAF Large Grant 2022 ‘Extragalactic Surveys with JWST’ (PI Pentericci), the INAF Mini\r\nGrant ‘1.05.24.07.01 RSN1: Spatially-Resolved Near-IR Emission of Intermediate-Redshift Jellyfish Galaxies’ (PI Watson), and are supported by the European Union – NextGenerationEU RFF M4C2 1.1 PRIN 2022 project 2022ZSL4BL INSIGHT. MB acknowledges support from the ERC Advanced Grant FIRSTLIGHT and Slovenian national research agency ARIS through grants N1-0238 and P1-0188. ","date_updated":"2025-11-24T09:07:25Z","article_type":"original","page":"1915-1925","quality_controlled":"1","oa_version":"Published Version","file":[{"creator":"dernst","file_id":"20674","file_name":"2025_MonthlyNoticesRAS_Dalmasso.pdf","file_size":1952887,"success":1,"checksum":"2caff0a3b81fed114408377323298b43","date_updated":"2025-11-24T09:02:04Z","date_created":"2025-11-24T09:02:04Z","access_level":"open_access","content_type":"application/pdf","relation":"main_file"}],"citation":{"apa":"Dalmasso, N., Watson, P. J., Treu, T., Trenti, M., Vulcani, B., Nanayakkara, T., … Pentericci, L. (2025). Quantifying spectroscopic flux variations between JWST NIRISS and NIRSpec: Slit losses in emission line measurements of z ∼ 1-3 galaxies. <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press. <a href=\"https://doi.org/10.1093/mnras/staf1837\">https://doi.org/10.1093/mnras/staf1837</a>","short":"N. Dalmasso, P.J. Watson, T. Treu, M. Trenti, B. Vulcani, T. Nanayakkara, M. Bradač, T. Jones, K. Boyett, X. Wang, S. Mascia, L. Pentericci, Monthly Notices of the Royal Astronomical Society 544 (2025) 1915–1925.","mla":"Dalmasso, Nicolò, et al. “Quantifying Spectroscopic Flux Variations between JWST NIRISS and NIRSpec: Slit Losses in Emission Line Measurements of z ∼ 1-3 Galaxies.” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 544, no. 2, Oxford University Press, 2025, pp. 1915–25, doi:<a href=\"https://doi.org/10.1093/mnras/staf1837\">10.1093/mnras/staf1837</a>.","chicago":"Dalmasso, Nicolò, Peter J. Watson, Tommaso Treu, Michele Trenti, Benedetta Vulcani, Themiya Nanayakkara, Maruša Bradač, et al. “Quantifying Spectroscopic Flux Variations between JWST NIRISS and NIRSpec: Slit Losses in Emission Line Measurements of z ∼ 1-3 Galaxies.” <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press, 2025. <a href=\"https://doi.org/10.1093/mnras/staf1837\">https://doi.org/10.1093/mnras/staf1837</a>.","ama":"Dalmasso N, Watson PJ, Treu T, et al. Quantifying spectroscopic flux variations between JWST NIRISS and NIRSpec: Slit losses in emission line measurements of z ∼ 1-3 galaxies. <i>Monthly Notices of the Royal Astronomical Society</i>. 2025;544(2):1915-1925. doi:<a href=\"https://doi.org/10.1093/mnras/staf1837\">10.1093/mnras/staf1837</a>","ieee":"N. Dalmasso <i>et al.</i>, “Quantifying spectroscopic flux variations between JWST NIRISS and NIRSpec: Slit losses in emission line measurements of z ∼ 1-3 galaxies,” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 544, no. 2. Oxford University Press, pp. 1915–1925, 2025.","ista":"Dalmasso N, Watson PJ, Treu T, Trenti M, Vulcani B, Nanayakkara T, Bradač M, Jones T, Boyett K, Wang X, Mascia S, Pentericci L. 2025. Quantifying spectroscopic flux variations between JWST NIRISS and NIRSpec: Slit losses in emission line measurements of z ∼ 1-3 galaxies. Monthly Notices of the Royal Astronomical Society. 544(2), 1915–1925."},"publication_identifier":{"eissn":["1365-2966"],"issn":["0035-8711"]},"has_accepted_license":"1","month":"12","title":"Quantifying spectroscopic flux variations between JWST NIRISS and NIRSpec: Slit losses in emission line measurements of z ∼ 1-3 galaxies","abstract":[{"text":"We analyse James Webb Space Telescope (JWST) Near Infrared Imager and Slitless Spectrograph (NIRISS) and Near Infrared Spectrograph (NIRSpec) spectroscopic observations in the Abell 2744 galaxy cluster field. From approximately 120 candidates, we identify 12 objects with at least two prominent emission lines among [O II] λ3727, H β λ4861, [O III] λ4959, [O III] λ5007, and H α λ6563 that are spectroscopically confirmed by both instruments. Our key findings reveal systematic differences between the two spectrographs based on source morphology and shutter aperture placement. Compact objects show comparable or higher\r\nintegrated flux in NIRSpec relative to NIRISS (within 1σ uncertainties), while extended sources consistently display higher flux in NIRISS measurements. This pattern reflects NIRSpec’s optimal coverage for compact objects while potentially undersampling extended sources. Quantitative analysis demonstrates that NIRSpec recovers at least 63 per cent of NIRISS-measured flux when the slit covers >15 per cent of the source or when Re < 1 kpc. For lower coverage or larger effective radii, the recovered flux varies from 24 per cent to 63 per cent. When studying the H α λ6563/[O III] λ5007 emission line ratio, we observe that\r\nmeasurements from these different spectrographs can vary by up to ∼0.3 dex, with significant implications for metallicity and star formation rate characterizations for individual galaxies. These results highlight the importance of considering instrumental effects when combining multi-instrument spectroscopic data and demonstrate that source morphology critically influences flux\r\nrecovery between slit-based and slitless spectroscopic modes in JWST observations.","lang":"eng"}],"author":[{"full_name":"Dalmasso, Nicolò","last_name":"Dalmasso","first_name":"Nicolò"},{"last_name":"Watson","full_name":"Watson, Peter J.","first_name":"Peter J."},{"first_name":"Tommaso","last_name":"Treu","full_name":"Treu, Tommaso"},{"first_name":"Michele","full_name":"Trenti, Michele","last_name":"Trenti"},{"first_name":"Benedetta","full_name":"Vulcani, Benedetta","last_name":"Vulcani"},{"last_name":"Nanayakkara","full_name":"Nanayakkara, Themiya","first_name":"Themiya"},{"first_name":"Maruša","last_name":"Bradač","full_name":"Bradač, Maruša"},{"last_name":"Jones","full_name":"Jones, Tucker","first_name":"Tucker"},{"last_name":"Boyett","full_name":"Boyett, Kristan","first_name":"Kristan"},{"full_name":"Wang, Xin","last_name":"Wang","first_name":"Xin"},{"first_name":"Sara","last_name":"Mascia","full_name":"Mascia, Sara","id":"edaf889c-c7cd-11ef-ab1b-bb28c431bd29"},{"last_name":"Pentericci","full_name":"Pentericci, Laura","first_name":"Laura"}],"issue":"2","_id":"20661","doi":"10.1093/mnras/staf1837","DOAJ_listed":"1","publication":"Monthly Notices of the Royal Astronomical Society","article_processing_charge":"Yes","OA_type":"gold","date_created":"2025-11-23T23:01:38Z","year":"2025","language":[{"iso":"eng"}],"publisher":"Oxford University Press","arxiv":1,"file_date_updated":"2025-11-24T09:02:04Z","tmp":{"short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png"},"oa":1,"PlanS_conform":"1","external_id":{"arxiv":["2510.27036"]},"volume":544,"publication_status":"published","department":[{"_id":"JoMa"}],"date_published":"2025-12-01T00:00:00Z","OA_place":"publisher","ddc":["520"],"intvolume":"       544","status":"public","scopus_import":"1","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","type":"journal_article"}