The JWST Ultramassive Galaxy Sample -- I. Overview, Photometry, and Stellar Kinematics: Selecting Optimal Template Subsets via Non-Negative Matrix Factorization

@misc{cappellari2026jwst,
  title = {{The JWST Ultramassive Galaxy Sample -- I. Overview, Photometry, and Stellar Kinematics: Selecting Optimal Template Subsets via Non-Negative Matrix Factorization}},
  author = {Michele Cappellari and Dieu D. Nguyen and Susan A. Kassin},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.21979},
  eprint = {2609.21979},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.21979},
}

TY  - UNPB
TI  - The JWST Ultramassive Galaxy Sample -- I. Overview, Photometry, and Stellar Kinematics: Selecting Optimal Template Subsets via Non-Negative Matrix Factorization
AU  - Michele Cappellari
AU  - Dieu D. Nguyen
AU  - Susan A. Kassin
PY  - 2026
DA  - 2026/09/18
PB  - arXiv
DO  - 10.48550/arxiv.2609.21979
UR  - https://arxiv.org/abs/2609.21979
AB  - We introduce the JWST Ultramassive Galaxy Sample, comprising 8 extreme early-type galaxies (M_⋆ ≳ 2×10^12 M_⊙) 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 μm 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.
ER  -