{
  "abstract": "Wide-field slitless spectroscopy (WFSS) is a powerful tool for studying large samples of galaxies across cosmic time. With the arrival of JWST, and its NIRCAM grism mode, slitless spectroscopy can reach a medium spectral resolution of (R ∼ 1600), allowing it to spatially resolve the ionised-gas kinematics out to z ∼ 9. However, the kinematic information is convolved with morphology along the dispersion axis, a degeneracy that must be modelled to recover intrinsic properties. We present the Grism Emission-line Kinematics tOol (geko), a Python package that forward-models NIRCam grism observations and infers emission-line morphologies and kinematics within a Bayesian framework. geko combines Sérsic surface-brightness models with arctangent rotation curves, includes full point-spread function (PSF) convolution and forward-modelling of the grism dispersion, and leverages gradient-based sampling via jax/numpyro for efficient inference. It recovers parameters such as effective radius, velocity dispersion, rotational velocity, rotational support, and dynamical mass, with typical run times of ∼20 minutes per galaxy on GPUs. We validate performance using extensive mock data spanning position angle, S/N, and morphology, quantifying where degeneracies limit recovery. Finally, we demonstrate applications to real FRESCO Hα emitters at z ≈ 4 − 6, recovering both rotation- and dispersion-dominated systems. geko opens the way to statistical studies of galaxy dynamics in the early Universe and is publicly available at https://github.com/angelicalola-danhaive/geko.",
  "abstract_shown": true,
  "affiliations": [
    "Kavli Institute for Cosmology, University of Cambridge , Madingley Road, Cambridge, CB3 0HA ,",
    "Cavendish Laboratory, University of Cambridge , 19 JJ Thomson Avenue, Cambridge, CB3 0HE ,"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 2,
  "authors": [
    {
      "affs": [
        0,
        1
      ],
      "name": "A Lola Danhaive",
      "orcid": "0000-0002-9708-9958"
    },
    {
      "affs": [
        0,
        1
      ],
      "name": "Sandro Tacchella",
      "orcid": "0000-0002-8224-4505"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/8cckxzppqxjr4.bib",
  "cited_by": 0,
  "doi": "10.1093/mnras/stag1965",
  "fulltext_url": null,
  "id": "8cckxzppqxjr4",
  "issns": [
    "0035-8711",
    "1365-2966"
  ],
  "landing_url": "https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1965/8931747",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3103|Galaxies: Formation, Evolution, Phenomena"
    ]
  ],
  "openalex": "W7222529164",
  "pdf_url": "https://academic.oup.com/mnras/advance-article-pdf/doi/10.1093/mnras/stag1965/72051932/stag1965.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-16",
  "publisher": "Oxford University Press (OUP)",
  "ris": "https://research.draconitic.com/paper/8cckxzppqxjr4.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:17Z",
      "native_id": "10.1093/mnras/stag1965",
      "source": "crossref",
      "url": "https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1965/8931747"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "openalex:3103|Galaxies: Formation, Evolution, Phenomena",
      "subfield": "galaxies"
    }
  ],
  "title": "geko : A tool for modelling galaxy kinematics and morphology in JWST /NIRCam slitless spectroscopic observations",
  "title_text": "geko : A tool for modelling galaxy kinematics and morphology in JWST /NIRCam slitless spectroscopic observations",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:17Z",
  "url": "https://research.draconitic.com/paper/8cckxzppqxjr4",
  "venue": "Monthly Notices of the Royal Astronomical Society",
  "versions": []
}