{
  "abstract": "We introduce the JWST Ultramassive Galaxy Sample, comprising 8 extreme early-type galaxies ($M_\\star \\gtrsim 2\\times10^{12}\\,\\mathrm{M}_\\odot$) drawn as a representative subset from a comprehensive full-sky census of over 100 such objects. This program aims to dynamically measure their central supermassive black holes (BHs) to probe the extreme high-mass end of BH--galaxy scaling relations, a critical regime where the physical mechanisms governing BH growth and host-galaxy co-evolution are expected to fundamentally change. In this first paper, we present the foundational data products: detailed photometric models and spatially resolved nuclear stellar kinematics. To accurately map the stellar mass distribution from the BH sphere of influence out to the extended halo, we combine diffraction-limited JWST/NIRCam imaging with wide-field DESI Legacy Surveys data, parametrizing the surface brightness using Multi-Gaussian Expansion (MGE). We extract stellar kinematics from JWST/NIRSpec integral-field observations using the penalized pixel-fitting (\\textsc{pPXF}) method. To fully exploit the continuous $1.66-3.17\\,μ\\mathrm{m}$ wavelength coverage---avoiding the telluric gaps of ground-based empirical libraries and the computational burden of massive theoretical grids---we introduce the use of near-separable Non-Negative Matrix Factorization (NMF). This algorithm identifies an optimal, highly compressed subset of synthetic spectra from the updated BOSZ library, perfectly capturing its spanning power at a fraction of the computational cost. The resulting kinematic maps reveal that these ultramassive systems are overwhelmingly slow rotators, frequently harboring kinematically decoupled cores. These high-quality photometric and kinematic data provide the inputs required for the robust Jeans Anisotropic Modelling (JAM) of the central BH masses in Paper II.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.21979",
  "author_total": 3,
  "authors": [
    {
      "name": "Michele Cappellari"
    },
    {
      "name": "Dieu D. Nguyen"
    },
    {
      "name": "Susan A. Kassin"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/3c6zp3gkep1je.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.21979",
  "fulltext_url": null,
  "id": "3c6zp3gkep1je",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.21979",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "openalex",
      "3103|Galaxies: Formation, Evolution, Phenomena"
    ]
  ],
  "openalex": "W7213870938",
  "pdf_url": "https://arxiv.org/pdf/2609.21979",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-18",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/3c6zp3gkep1je.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:23:03Z",
      "native_id": "2609.21979",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.21979"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "The JWST Ultramassive Galaxy Sample -- I. Overview, Photometry, and Stellar Kinematics: Selecting Optimal Template Subsets via Non-Negative Matrix Factorization",
  "title_text": "The JWST Ultramassive Galaxy Sample -- I. Overview, Photometry, and Stellar Kinematics: Selecting Optimal Template Subsets via Non-Negative Matrix Factorization",
  "type": "preprint",
  "updated_at": "2026-10-30T12:23:03Z",
  "url": "https://research.draconitic.com/paper/3c6zp3gkep1je",
  "venue": "arXiv",
  "versions": []
}