Jeans Dynamical Constraints on the IMF in Massive Quiescent Galaxies at z∼0.7 from JWST/NIRSpec
Abstract
We present dynamical masses for nine massive quiescent galaxies at z∼0.7 from the JWST-IMFERNO program, measured from ultra-deep (∼32hr), spatially resolved NIRSpec/MSA spectroscopy combined with NIRCam imaging. The most massive of these galaxies have previously been found to have a bottom-heavy initial mass function (IMF), based on measurements of dwarf-sensitive absorption features. Here, we examine whether the stellar masses inferred for these IMFs are consistent with the dynamical masses of these galaxies. We derive the dynamical masses by including Jeans Anisotropic Modelling within a forward-modelling framework that accounts for instrumental optics, source morphology, and geometric effects. We compare the resulting dynamical masses to the stellar masses for different IMF assumptions. A Milky Way IMF produces physically plausible dynamical-to-stellar mass ratios but implies central dark matter fractions (fDM,1Re=0.54±0.06) that are a factor ∼2 higher compared to local ETGs and simulations. When uniformly applying the IMF that was measured from absorption features, the mean dark matter fraction becomes low (fDM,1Re=0.02±0.18), and the stellar masses exceed the dynamical mass at 2σ significance for two out of seven galaxies in the sample. When we adopt the measured IMF only in the central Re and use a MW IMF in the outskirts, we find realistic dark matter fractions (fDM,1Re=0.28±0.12) and consistent dynamical masses. These results support a scenario where the cores of the most massive quiescent galaxies at z∼0.7 had a bottom-heavy IMF, similar to those observed in the centres of local early-type galaxies. Our results are consistent with an inside-out growth scenario, in which size and mass growth of massive galaxies proceeds after quenching through minor mergers, leaving the bottom-heavy cores mostly intact.
Related
- The Role of Environment in Shaping the Assembly Timelines of Massive Quiescent Galaxies at Cosmic Noon
- Where Galaxies Go to Die: The Environments of Massive Quiescent Galaxies at 3 < z < 5
- How Quickly Did the Giants Form? Constraining the Formation Timescales of Massive Quiescent Galaxies at Cosmic Noon Using Chemical Evolution Modelling
- The Size-Mass Relation and Inside-Out Quenching of Massive Quiescent Galaxies at 2<z<3 with JWST PRIMER and MINERVA
- PANORAMIC: The Dawn of Massive Quiescent Galaxies. I. Number Density and Cosmic Variance from 1000 arcmin ² NIRCam Imaging
BibTeX
@misc{slob2026jeans,
title = {{Jeans Dynamical Constraints on the IMF in Massive Quiescent Galaxies at $z\sim0.7$ from JWST/NIRSpec}},
author = {Martje Slob and Mariska Kriek and Chloe M. Cheng and Arjen van der Wel and Aliza G. Beverage and Rachel Bezanson and Charlie Conroy and Anna de Graaff and Elham Eftekhari and Robert Feldmann and Wout M. Goesaert and Meng Gu and Joel Leja and Brian Lorenz and Pavel E. Mancera Piña and Ignacio Martín-Navarro and Andrew B. Newman and Sedona H. Price and Alice E. Shapley and Katherine A. Suess and Jesse van de Sande and Pieter van Dokkum},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.08612},
eprint = {2611.08612},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.08612},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Jeans Dynamical Constraints on the IMF in Massive Quiescent Galaxies at z∼0.7 from JWST/NIRSpec
AU - Martje Slob
AU - Mariska Kriek
AU - Chloe M. Cheng
AU - Arjen van der Wel
AU - Aliza G. Beverage
AU - Rachel Bezanson
AU - Charlie Conroy
AU - Anna de Graaff
AU - Elham Eftekhari
AU - Robert Feldmann
AU - Wout M. Goesaert
AU - Meng Gu
AU - Joel Leja
AU - Brian Lorenz
AU - Pavel E. Mancera Piña
AU - Ignacio Martín-Navarro
AU - Andrew B. Newman
AU - Sedona H. Price
AU - Alice E. Shapley
AU - Katherine A. Suess
AU - Jesse van de Sande
AU - Pieter van Dokkum
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2611.08612
UR - https://arxiv.org/abs/2611.08612
AB - We present dynamical masses for nine massive quiescent galaxies at z∼0.7 from the JWST-IMFERNO program, measured from ultra-deep (∼32hr), spatially resolved NIRSpec/MSA spectroscopy combined with NIRCam imaging. The most massive of these galaxies have previously been found to have a bottom-heavy initial mass function (IMF), based on measurements of dwarf-sensitive absorption features. Here, we examine whether the stellar masses inferred for these IMFs are consistent with the dynamical masses of these galaxies. We derive the dynamical masses by including Jeans Anisotropic Modelling within a forward-modelling framework that accounts for instrumental optics, source morphology, and geometric effects. We compare the resulting dynamical masses to the stellar masses for different IMF assumptions. A Milky Way IMF produces physically plausible dynamical-to-stellar mass ratios but implies central dark matter fractions (f_DM,1R_e=0.54±0.06) that are a factor ∼2 higher compared to local ETGs and simulations. When uniformly applying the IMF that was measured from absorption features, the mean dark matter fraction becomes low (f_DM,1R_e=0.02±0.18), and the stellar masses exceed the dynamical mass at 2σ significance for two out of seven galaxies in the sample. When we adopt the measured IMF only in the central R_e and use a MW IMF in the outskirts, we find realistic dark matter fractions (f_DM,1R_e=0.28±0.12) and consistent dynamical masses. These results support a scenario where the cores of the most massive quiescent galaxies at z∼0.7 had a bottom-heavy IMF, similar to those observed in the centres of local early-type galaxies. Our results are consistent with an inside-out growth scenario, in which size and mass growth of massive galaxies proceeds after quenching through minor mergers, leaving the bottom-heavy cores mostly intact.
ER -